Patent Publication Number: US-11665192-B2

Title: Generating a segmentation policy based on vulnerabilities

Description:
CROSS REFERENCES TO RELATED APPLICATION 
     This application is a continuation of U.S. application Ser. No. 15/902,954, filed Feb. 22, 2018, now U.S. Pat. No. 11,075,937, which is incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     Technical Field 
     This application relates to managing a segmentation policy that controls communications between workloads. 
     SUMMARY 
     A system, non-transitory computer-readable storage medium, and method generates vulnerability information relating to workloads executing on one or more processing devices in a segmented computing environment. A segmentation server obtains a segmentation policy representing permitted connectivity between the workloads. The segmentation server identifies vulnerabilities associated with respective ports of the workloads. The segmentation server determines vulnerability scores associated with each of the identified vulnerabilities for each of the respective ports. The segmentation server determines exposure scores for the respective ports. Here, an exposure score for a particular port represents a measure of exposure of the particular port to other networked devices based on the current segmentation policy. The segmentation server combines the vulnerability scores with the respective exposure scores for the respective ports to generate vulnerability exposure scores for the respective ports. The segmentation server generates a presentation of vulnerability exposure information based on the vulnerability exposure scores. The segmentation server outputs the presentation of the vulnerability exposure information. 
     In an embodiment, the exposure score can comprise an intra-group exposure score representing a measure of connectivity of the particular port to other workloads within a group associated with a workload of the particular port. In another embodiment, the exposure score can comprise an inter-group exposure score representing a measure of connectivity of the particular port to other workloads outside the group associated with a workload of the particular port. In yet another embodiment, the exposure score can comprise a total exposure score representing a measure of connectivity of the particular port to any other workloads. 
     In an embodiment, generating the presentation includes the segmentation server aggregating for workloads within a tier, the vulnerability exposure scores for each port number to generate port number scores for each port number. A ranked list of port numbers is generated based on the port number scores. 
     In an embodiment, generating the presentation includes the segmentation server identifying tiers of workloads in which each of the tiers comprising a group of workloads having common label values across two ore label dimensions. The segmentation server aggregates the vulnerability exposure scores across workloads in each of the tiers to generate tier-level scores for each of the tiers. The segmentation server generates a representation of a tier-level segmentation policy graph comprising nodes representing the tiers and edges representing connectivity between workloads in different ones of the tiers. The segmentation server associates the tier-level scores with corresponding nodes in the tier-level segmentation policy graph. 
     In an embodiment, the segmentation server determines the exposure scores by generating a count of a number of workloads permitted to connect to a particular port under the current segmentation policy, and generating an exposure score for the particular port based at least in part on the count. The segmentation server may furthermore identify an external network permitted to connect to a particular port under the current segmentation policy, obtain a predefined score associated with the external network, and generate an exposure score for the particular port based in part on the predefined score associated with the external network. The segmentation server may furthermore identify an exposure score for a connecting port permitted to connect to a particular port under the current segmentation policy, and generate the exposure score for the particular port based in part on the exposure score for the connecting port. 
     In other embodiments, a system, non-transitory computer-readable storage medium, and method generate a modified segmentation policy based on vulnerability information. The segmentation server obtains a current segmentation policy representing permitted connectivity between workloads executing on one or more processing devices in a segmented computing environment. The segmentation server furthermore identifies vulnerabilities associated with respective ports of the workloads. The segmentation server generates vulnerability exposure scores for the ports on the workloads under the current segmentation policy. Here, the vulnerability exposure scores represent a measure of exposure to the vulnerabilities under the current segmentation policy. The segmentation server observes communications between the workloads under the current segmentation policy to generate a traffic flow graph. The segmentation server generates a modified segmentation policy based on the vulnerability exposure scores and the traffic flow graph. The modified segmentation policy reduces exposure to the vulnerabilities relative to the current segmentation policy. The segmentation server generates management instructions based on the modified segmentation policy to enforce the modified segmentation policy. The segmentation server sends the management instructions to operating system instances executing the workloads. 
     In example embodiment, the segmentation server detects, in a first group of workloads, a vulnerable port on which one of the vulnerabilities exists. The segmentation server detects connectivity using the vulnerable port between the first group of workloads and a second group of workloads in the traffic flow graph. Furthermore, the segmentation server detects a lack of connectivity between the first group of workloads having the vulnerable port and a third group of workloads in the traffic flow graph. In an embodiment, the current segmentation policy permits the connectivity between the first group of workloads and the third group of workloads. The segmentation server generates the modified segmentation policy to limit permitted communications of the first group of workloads to the second group of workloads without permitting communications between the first group of workloads and the third group of workloads. 
     In another example embodiment, the segmentation server detects, in a first group of workloads, a vulnerable port on which one of the vulnerabilities exists. The segmentation server furthermore detects a lack of connectivity using the vulnerable port between the first group of workloads and a second group of workloads in the traffic flow graph. In an embodiment, the current segmentation policy permits the connectivity using the vulnerable port between the first and second groups of workloads. The segmentation server furthermore detects connectivity using one or more non-vulnerable ports between the first group of workloads and the second group of workloads in the traffic flow graph. The segmentation server generates the modified segmentation policy to limit permitted communications between the first group of workloads and the second group of workloads to using the one or more non-vulnerable ports without permitting communications between the first group of workloads and the second group of workloads using the vulnerable port. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a high-level block diagram illustrating an environment for managing a segmentation policy, according to one embodiment. 
         FIG.  2    is a block diagram illustrating example embodiments of operating system instances. 
         FIG.  3    is a block diagram illustrating an example embodiment of a segmentation server. 
         FIG.  4    is a diagram illustrating an example presentation of vulnerability exposure information associated with workloads in a segmented computing environment. 
         FIG.  5    is a diagram illustrating example graphs associated with a first technique for generating a modified segmentation policy to reduce exposure to vulnerabilities. 
         FIG.  6    is a diagram illustrating example graphs associated with a second technique for generating a modified segmentation policy to reduce exposure to vulnerabilities. 
         FIG.  7    is a flowchart illustrating an example process for generating vulnerability exposure scores associated with workloads in a segmented computing environment. 
         FIG.  8    is a flowchart illustrating an example process for generating a presentation of aggregate vulnerability exposure information associated with workloads in a segmented computing environment. 
         FIG.  9    is a flowchart illustrating an example process for generating rules for a segmentation policy based on vulnerabilities. 
     
    
    
     DETAILED DESCRIPTION 
     The Figures (FIGS.) and the following description describe certain embodiments by way of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles described herein. Reference will now be made to several embodiments, examples of which are illustrated in the accompanying figures. It is noted that wherever practicable similar or like reference numbers may be used in the figures and may indicate similar or like functionality. 
     A segmentation server generates vulnerability exposure scores associated with ports on workloads operating in a segmented computing environment. The vulnerability exposure scores represent the potential exposure of the respective ports to detected vulnerabilities. The segmentation server may automatically aggregate the vulnerability exposure scores in various ways to generate vulnerability exposure information representative of different groups of workloads. The aggregated vulnerability exposure information may be presented in a manner that enables an administrator to easily evaluate different segmentation strategies and assess the risks associated with each of them. Moreover, the segmentation server can automatically generate a recommended segmentation policy according to a desired segmentation strategy. The desired segmentation strategy may be automatically modified based on the vulnerability exposure scores to reduce exposure to certain vulnerabilities without impeding operation of the workloads. As a result, the workloads can operate with improved security relative to conventional computing environments. 
       FIG.  1    is a high-level block diagram illustrating a networked computing environment  100 . The networked computing environment  100  includes a segmentation server  120 , a network  110 , an administrative client  160 , and an administrative domain  150  that includes a plurality of operating system (OS) instances  130  (e.g., OS instances  130 - 1 ,  130 - 2 , . . . ,  130 -N). The administrative domain  150  can correspond to an enterprise such as, for example, a service provider, a corporation, a university, or a government agency under control of the segmentation server  120 . 
     The network  110  represents the communication pathways between the segmentation server  120 , the administrative client  160 , and the OS instances  130 . In one embodiment, the network  110  uses standard communications technologies and/or protocols and can include the Internet. In another embodiment, the entities on the network  110  can use custom and/or dedicated data communications technologies. 
     The OS instances  130  comprise instances of an operating system executing on one or more computing devices. An OS instance  130  may execute directly on a physical machine or on a virtual machine that executes on one or more computing devices. A single physical or virtual machine may operate a single OS instance  130  or may operate multiple OS instances  130  The OS instances  130  each execute one or more workloads  138  (e.g., one or more workloads  138 - 1 , one or more workloads  138 - 2 , etc.). The workloads  138  comprise independently addressable computing units for performing computing tasks. A workload  138  may comprise, for example, an application or application component, a process, a container, or other sub-component thereof executing on the OS instance  130 . In some instances, an OS instance  130  may operate only a single workload  138 . In other instances, an OS instance  130  may operate multiple workloads  138  that may be independently addressable and may perform different independent computing functions. The workloads  138  on the OS instances  130  may communicate with other workloads  138  on different OS instances  130  within the administrative domain  150  to perform various tasks. 
     A workload  138  communicates over one or more ports  134 . A port  134  comprises a logical communication endpoint for a particular service that is provided by or used by a workload  138 . A port  134  on a workload  138  may be identified by a port identifier that may specify, for example, an IP address associated with the workload  138  and a port number. Specific port numbers may be used consistently across different workloads  138  in association with specific services. Thus, the port number can often identify the service and vice versa. For example, port  80  is typically used for hyper-text transfer protocol (HTTP) traffic on any workloads  138  that provide or consume HTTP-based web services and port  5432  is typically used for any TCP traffic associated with PostgreSQL database services. In other instances, the same services on different workloads  138  may utilize different port numbers that are not necessarily consistent, or different services may utilize the same port numbers. 
     The segmentation server  120  is a computer (or set of computers) that obtains and stores information about the OS instances  130  on the network  120  and the workloads  138  executing on the OS instances  130 . The segmentation server  120  manages a segmentation policy for the administrative domain  150  that regulates communications between workloads  138  within the administrative domain  150 . In an embodiment, the segmentation policy is set forth using permissive rules that specify the communications that are permitted. The segmentation policy is enforced by blocking any communications that are not expressly permitted by the rules. For example, the segmentation policy includes a set of rules specifying whether certain workloads  138  are allowed to provide services to or receive services from other workloads  138 , and may place restrictions on how those workloads  138  are allowed to communicate when providing or consuming the services. For example, a segmentation policy may include a rule specifying that a workload  138 - 1  operating on an OS instance  130 - 1  is allowed to provide a particular service to a workload  138 - 2  operating on an OS instance  130 - 2 . Absent other rules, the workload  138 - 1  will thus be blocked from providing the service to a workload  138 -N operating on an OS instance  130 -N. The rule may furthermore specify the type of service that the workload  138 - 1  is allowed to provide to workload  138 - 2  (e.g., a database service, a web service, etc.). Additionally, the rule may specify how the workloads  138 - 1 ,  138 - 2  may communicate when providing this service (e.g., using encrypted communication only, using authenticated communication only, etc.). A rule may be specified as a plurality of fields including a “service,” a “provided-by” portion that identifies one or more workloads  138  that is permitted to provide the service (which may be specified by a port number), a “used-by” portion that identifies one or more workloads  138  that is permitted to use the service provided by the workloads  138  in the “provided-by portion,” and a “rule function” that may place one or more restrictions on the communications between the workloads  138  while facilitating the service. 
     In an embodiment, the segmentation server  120  may assign one or more labels to each workload  138  that define one or more high-level characteristics of the workload  138 . Labels may be multi-dimensional. Here, a label may comprise a “dimension” (a high-level characteristic) and a “value” (the value of that high-level characteristic). For example, one possible label dimension may specify a “role” of the workload  138  and may have values such as “web,” “API,” or “database” specifying the role of the workload  138  within the administrative domain  150 . In another example, a label dimension may specify a “location” of the workload  138  and may have values such as “United States” or “Europe.” Workloads  138  may also be labeled based on a user group of a user that is logged into the workload  138  or the corresponding OS instance  130  on which the workload  138  executes. For example, a workload  138  may have a label with a dimension “user group” and a value “managers.” Each workload  138  may be assigned labels for one or more dimensions but each workload  138  does not necessarily have a label assigned for every possible dimension. For example, a workload  138  may have a label specifying its location but may not necessarily have a label specifying its role. The set of labels assigned to a particular workload  138  may be referred to herein as a label set for the workload  138 . 
     A logical management model specifying the number and types of dimensions available and those dimensions&#39; possible values may be configurable. In one embodiment, the logical management model includes the following dimensions and possible values, as shown in Table 1: 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Example of logical management model 
               
            
           
           
               
               
            
               
                 Dimension 
                 Meaning (M), Values (V) 
               
               
                   
               
               
                 Role 
                 M: The role of the managed server within the 
               
               
                   
                 administrative domain. 
               
               
                   
                 V: web, API, database 
               
               
                 Environment 
                 M: The lifecycle stage of the managed server. 
               
               
                   
                 V: production, staging, development 
               
               
                 Application 
                 M: The logical application (higher-level grouping 
               
               
                   
                 of managed servers) to which the managed server 
               
               
                   
                 belongs. 
               
               
                   
                 V: trading, human resources 
               
               
                 Line of Business 
                 M: The business unit to which the managed 
               
               
                   
                 server belongs. 
               
               
                   
                 V: marketing, engineering 
               
               
                 Location 
                 M: The location of the managed server. Can be 
               
               
                   
                 physical (e.g., country or geographical region) or 
               
               
                   
                 logical (e.g., network). Physical is particularly 
               
               
                   
                 useful for expressing geographic compliance 
               
               
                   
                 requirements. 
               
               
                   
                 V: US or EU (physical), us-west-1 or us-east-2 
               
               
                   
                 (logical) 
               
               
                 User Group 
                 M: The user group containing the user logged 
               
               
                   
                 onto the managed server. 
               
               
                   
                 V: Engineers, Contractors, Managers, System 
               
               
                   
                 Administrators 
               
               
                   
               
            
           
         
       
     
     Workloads  138  may be logically grouped based on their respective label sets. An “application group” may be defined as a group of workloads  138  having the same label values for a predefined subset of label dimensions without necessarily having the same values in the other dimensions. For example, in one embodiment, an application group could be defined to include all workloads having the same label values in each of the “environment” and “application” dimensions. Alternatively, an application group could be defined to include all workloads having the same label values in each of the “environment,” “application” and “location” dimensions. A “tier” may be defined as a group of workloads  138  within an application group that have the same label value for at least one additional label dimension distinct from the label dimensions defining the application group. For example, a tier may be defined as group of workloads  138  having the same label values for the “environment,” “application,” and “role” labels. Alternatively, a “tier” may be defined as a group of workloads  138  having the same label values for the “environment,” “application,” “role,” and “location” dimensions. In some embodiments, the specific label dimensions used to define an application group and a tier may be configurable by an administrator. 
     The segmentation server  120  may utilize label sets to enable the segmentation policy to be defined at a high level of abstraction by specifying rules based on label sets. Thus, a rule of the segmentation policy may identify a group of workloads  138  to which a portion of the rule is applicable by referencing one or more label sets. For example, a rule may specify that a first group of workloads  138  with a label set A may provide a service B to a second group of workloads  138  with a label set C. Rules may be specified for groups of workloads  138  identified using only a subset of the label dimensions. For example, the segmentation policy may specify rules that control communications between specified application groups or between specified tiers. 
     The segmentation server  120  may retain a repository storing information about the OS instances  130  and the workloads  138  managed by the segmentation server  120 . For example, the segmentation server  120  may store, for each OS instance  130 , an OS instance identifier that uniquely identifies the OS instance  130 , workload identifiers for workloads  138  associated with the OS instance  138 , and membership information indicating one or more groups of workloads  138  to which each workload  138  belong (e.g., as defined by the respective label sets for the workloads  138 ). 
     Table 2 illustrates an example of information stored by the segmentation server  120 . Here, the “ID” represents the OS instance identifier for each OS instance  130 . The workload ID(s) represent the workload identifier for the workload(s)  138  executing on each OS instance  130 . If only a single workload executes on a particular OS instance  130 , the workload ID may be synonymous with the OS instance ID (e.g., in the case of ID1 and IDn). If more than one workload  138  executes on a given OS instance  130 , the workload ID may include the OS instance ID in combination with a sub-identifier for the workload  138  (e.g., in the case of ID2). The sub-identifier may comprise, for example, an IP address or other identifier that uniquely identifies the workload  138  when taken in combination with the identifier for the OS instance  130 . The memberships represent groups to which one or more workloads  138  executing on the OS instance  130  belongs. Each group may correspond to a unique label set involving one or more dimensions (e.g., a combination of labels representing an application group, tier, or other group). 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Example of a Repository Table 
               
            
           
           
               
               
               
            
               
                 OS Instance ID 
                 Workload ID(s) 
                 Memberships 
               
               
                   
               
               
                 ID1 
                 ID1 
                 A, C, D 
               
               
                 ID2 
                 ID2 + subID1 
                 B, C 
               
               
                   
                 ID2 + subID2 
                 D 
               
               
                 • 
                   
                 • 
               
               
                 • 
                   
                 • 
               
               
                 • 
                   
                 • 
               
               
                 IDn 
                 IDn 
                 B, D, E, F 
               
               
                   
               
            
           
         
       
     
     Instead of enforcing the segmentation policy at a centralized device, the segmentation policy is instead enforced by at least a subset of the OS instances  130 . To enable enforcement of the segmentation policy, the segmentation server  120  generates a set of management instructions and distributes the management instructions to the OS instances  130 . The management instructions include the rules controlling communications between different groups of workloads  138  (e.g., specified by their label sets or directly by an identifier of the workload  138 ) and membership information indicating workloads  138  belonging to each group (e.g., which workloads  138  have certain label sets). For efficiency of distribution, the segmentation server  120  may send different management instructions to different OS instances  130  so that each OS instance  130  gets only the management instructions relevant to its operation. Here, the segmentation server  120  may determine which rules are relevant to a given OS instance  130  and distribute the relevant rules to that OS instance  130 . A rule may be deemed relevant to a particular OS instance  130  if that OS instance  130  executes one or more workloads  138  that belongs to a group (defined by one or more label sets) referenced by the rule. The segmentation server  120  may furthermore determine which membership information is relevant to each OS instance  130  and distribute the relevant membership information to each respective OS instance  130 . Here, membership information may be relevant to a particular OS instance  130  if it defines membership of a group referenced by a rule deemed relevant to the particular OS instance  130 . Further details of a segmentation system for controlling communications between OS instances  130  based on labels is described in U.S. Patent Application Publication No. 2014/0373091 entitled “Distributed Network Security Using a Logical Multi-Dimensional Label-Based Policy Model,” to Paul J. Kirner, et al., which is incorporated by reference herein. 
     The administrative client  160  comprises a computing device that may be operated by an administrator of the administrative domain  150  being managed by the segmentation server  120 . The administrative client  160  may execute an interface (e.g., via an application or web browser) that enables the administrator to interact with the segmentation server  120  to configure or view the segmentation policy. The interface may furthermore enable the administrator to obtain various information about the OS instances  130  and workloads  138  on the network  120  and view traffic flows between the workloads  138 . 
       FIG.  2    illustrates example embodiments of OS instances  130 . An OS instance  130  may correspond to a managed OS instance  230  or an unmanaged OS instance  240 . A managed OS instance  230  includes an enforcement modules  235  that enables the managed OS instance  230  to enforce the segmentation policy for the workloads  138  it executes. In contrast, the unmanaged OS instance  235  does not include an enforcement module  235  and is unable to directly contribute to enforcement of the segmentation policy. The segmentation server  120  thus only distributes management instructions to the managed OS instances  230 . Nevertheless, the unmanaged OS instances  240  may still be affected by the segmentation policy because the managed OS instances  230  may limit communications of its workloads  138  with workloads  138  on the unmanaged OS instance  240 . Workloads  138  executing on the unmanaged OS instances  240  may be assigned labels and may be referenced in the rules of the segmentation policy in the same way as workloads  138  on managed OS instances  130 . Thus, communications between workloads  138  on managed OS instances  230  and unmanaged OS instances  240  may be controlled by the segmentation policy by enforcing the rules at the managed OS instances  230 . 
     In some embodiments, the segmentation policy may be effectively enforced on an unmanaged OS instance  240  by a separate device that can control communications to and from the unmanaged OS instance  240  on which workloads  138  execute. For example, an enforcement module  235  on an upstream switch port or other device may control communications to and from workloads  138  on a downstream unmanaged OS instance  240 . In this case, the segmentation policy can be enforced directly on the workloads  138  on an unmanaged OS instance  240  similarly to enforcement on a managed OS instance  230 . 
     The enforcement module  235  includes a management module  232 , a management module configuration  234 , and a policy implementation module  236 . The management module  232  comprises a low-level network or security engine that controls incoming and outgoing traffic associated with each of the workloads  138  executing on the OS instance  130 . For example, the management module  232  may include an operating system-level firewall, an Internet Protocol security (IPsec) engine, or a network traffic filtering engine (e.g., based on the Windows Filtering Platform (WFP) development platform). The management module  132  on a given managed OS instance  230  restricts communications to or from the workloads  138  executing on the given managed OS instances  230  based on the management module configuration  134 . For example, the management module  232  may permit a particular workload  138  to communicate with a limited set of workloads  138  on other OS instances  130 , and may block all other communications. Furthermore, the management module  232  may place restrictions on how each workload  138  is permitted to communicate. For example, for a particular workload  138 , the management module  232  may enable the workload  138  to communicate using only encrypted protocols and block any unencrypted communications. 
     The policy implementation module  236  receives the management instructions from the segmentation server  120  and translates the management instructions from a high level of abstraction to a low level of abstraction represented by the management module configuration  234 . For example, the policy implementation module  236  may obtain the relevant rules and relevant membership information from the management instructions, and identify the specific workloads  138  and services controlled by the rules. The policy implementation module  236  then generates a management module configuration  234  that enables the management module  232  to enforce the management instructions. 
       FIG.  3    is a high-level block diagram of an embodiment of a segmentation server  120 . The segmentation server  120  comprises a segmentation graph module  302 , a traffic flow module  304 , a vulnerability exposure scoring module  306 , an aggregation module  308 , a rule generation module  310 , an instruction distribution module  312 , and a repository  350 . The repository  350  may comprise a workloads database  352  that stores associations between workloads  138  and their respective label sets, a rule database that stores a segmentation policy as a set of rules, and a vulnerabilities database  356  that stores information relating to detected vulnerabilities associated with workloads  138  in the administrative domain  150 . In alternative embodiments, the segmentation server  120  may include different or additional components. The various components of the segmentation server  120  may be implemented as one or more processors and a non-transitory computer-readable storage medium that stores instructions executed by the one or more processors to carry out the functions attributed to the segmentation server  120  described herein. 
     The segmentation policy graph module  302  generates a segmentation policy graph comprising a data structure representing the permitted (but not necessarily observed) connections between workloads  138  under the segmentation policy. In the segmentation policy graph, each workload  138  is represented by a node and permitted connections between workloads  138  are represented by edges between the respective nodes. The nodes may store information relating to the workloads  138  and the edges may store information relating to the permitted traffic between the workloads such as the permitted port numbers, protocols, and services permitted between the workloads  138 . 
     The segmentation policy graph module  302  may generate a segmentation policy graph that is limited to workloads within the scope of a specified label set. For example, the segmentation policy graph module  302  may generate a segmentation policy graph for a specific application group that is limited to rules affecting workloads  138  in the application group or may generate a segmentation policy graph for a specific tier that is limited to rules affecting workloads  138  within the specified tier. 
     The segmentation policy graph module  302  may furthermore generate segmentation policy graphs at different levels of abstraction. For example, the segmentation policy graph module  302  may generate a tier-level segmentation policy graph in which tiers of workloads  138  are represented as nodes and a permitted connection between one or more pairs of workloads  138  in different tiers are represented as edges between the nodes. In this representation, an edge exists between a first tier and a second tier if a rule permits a connection between any workload  138  in the first tier and any workload  138  in the second tier. Similarly, the segmentation policy graph module  308  may generate an application-level segmentation policy graph in which application groups are represented as nodes and a permitted connection between one or more pairs of workloads  138  in different application groups are represented as edges between the nodes. In this representation, an edge exists between a first application group and a second application group if a rule permits a connection between any workload  138  in the first application group and any workload  138  in the second application group. 
     The traffic flow module  304  monitors traffic between workloads  138  and presents information relating to the traffic flows. For example, the traffic flow module  304  may identify each pair of workloads  138  that communicate with each other during a particular time period. For each detected traffic flow between a pair of workloads  138 , the traffic flow module  304  may identify what services are communicated between the pair of workloads  138  and the corresponding ports  134  and protocols used in the communications. Furthermore, the traffic flow module  304  may identify statistical information relating to the traffic flow between a pair of workloads  138  such as, for example, a volume of data transferred between the pair of workloads within a particular time period, a frequency of communications between the pair of workloads  138 , a duration of communications between the pair of workloads  138 , or other statistical information indicative of the extent of the communications. For the purpose of monitoring the traffic flows, the traffic flow module  304  may operate under a very permissive segmentation policy (e.g., enabling all workloads  138  in the administrative to communicate with all workloads  138  over all ports and protocols) so that the traffic flows are representative of the normal operation of the workloads  138  in the administrative domain  150 . 
     The traffic flow module  304  may generate a data structure representing the traffic flows in the form of a traffic flow graph in which each workload  138  is represented by a node and a traffic flow between a pair of workloads  138  is represented by an edge connecting the respective nodes corresponding to the connected pair of workloads  138 . The nodes may store information relating to the workloads  138  and the edges may store information relating to the traffic flow such as the port number, service, process, protocol, or combination thereof associated with the traffic flow. In an embodiment, the traffic flow graph may be limited to traffic flows meeting predefined criteria. For example, the traffic flow graph may be limited to traffic flows meeting a predefined threshold volume of the traffic (e.g., amount of data, frequency, duration, or a combination thereof). Thus, pairs of workloads  138  having only very limited or sporadic communications may be omitted from the traffic flow graph. 
     The traffic flow module  304  may generate a traffic flow graph that is limited to workloads within the scope of a specified label set. For example, the traffic flow module  304  may generate a traffic flow graph for a specific application group that is limited to traffic flows involving workloads  138  in the application group. In another example, the traffic flow module  304  may generate a traffic flow graph for a specific tier that is limited to traffic flows involving workloads  138  within the specified tier. 
     The traffic flow module  304  may furthermore generate traffic flow graphs at different levels of abstraction. For example, the traffic flow module  304  may generate a tier-level traffic flow graph in which tiers of workloads  138  are represented as nodes and an observed connection between one or more pairs of workloads  138  in different tiers are represented as edges between the nodes. In this representation, a first tier is considered connected to a second tier if a traffic flow is observed between any workload  138  in the first tier and any workload  138  in the second tier. Similarly, the traffic flow module  304  may generate an application-level traffic flow graph in which application groups are represented as nodes and an observed connection between one or more pairs of workloads  138  in different application groups are represented as edges between the nodes. In this representation, a first application group is considered “connected” to a second application group if a traffic flow is observed between any workload  138  in the first application group and any workload  138  in the second application group. 
     The edges in a traffic flow graph and a segmentation policy graph may overlap to varying degree depending on how permissive the segmentation policy. For example, in a highly permissive segmentation policy, the number of edges in the segmentation policy graph may be significantly more than the number of edges in the traffic flow graph because only a subset of the permitted connections are actually utilized by the workloads  138 . In a less permissive segmentation policy, the number of edges in the segmentation policy graph may be similar to or the same as the number of edges in the traffic flow graph because the segmentation policy only permits traffic close to that observed. 
     The vulnerability exposure scoring module  306  generates vulnerability exposure scores associated with ports  134  of the workloads  138  in the administrative domain  150 . A vulnerability exposure score for a particular port  134  represents a measure of risk associated with a connection to the particular port  134 . 
     In an embodiment, a vulnerability exposure score for a particular port  134  may be generated based on one or more vulnerability scores of vulnerabilities associated with the particular port  134  and an exposure score representing a connectivity measure of the particular port  134 . The vulnerability exposure scoring module  306  may obtain vulnerability scores that identify vulnerabilities present on workloads  138  in the administrative domain  150  and provides scores associated with the identified vulnerabilities. For example, in an embodiment a vulnerability scanner executing on each workload  138  may scan the workload  138  for certain predefined characteristics defined in a list of known vulnerabilities and report detected vulnerabilities to the vulnerability exposure scoring module  306  (e.g., using a vulnerability identifier uniquely associated with the detected type of vulnerability). The vulnerability exposure scoring module  306  may then map the detected vulnerability to a score according to a predefined mapping. For example, in one embodiment, the vulnerability exposure scoring module  306  may utilize a Common Vulnerability Scoring System (CVSS) to generate the vulnerability scores. Particularly, an embodiment may utilize an Attack Vector (AV) metric in determining the vulnerability scores. In other embodiments, the vulnerability exposure scoring module  306  may obtain vulnerabilities and associated scores from a vulnerability scanner that executes externally to the workloads  138  (e.g., on a separate scanning server) to scan the workloads  138  and report the results of the scan to the vulnerability exposure scoring module  306 . 
     The vulnerability exposure scoring module  306  may obtain detection results for multiple different vulnerabilities on the same workload  138 . Furthermore, the same type of vulnerability (e.g., having the same vulnerability identifier) may be found on multiple different workloads. The scanning results may be stored to a table in the vulnerabilities database  356  with each entry in the table specifying (1) an identifier for the type of vulnerability found, (2) a port identifier associated with the vulnerability (e.g., identified by a workload identifier such as an IP address and a port number), and (3) a vulnerability score associated with the vulnerability. An example of a vulnerability table is provided in Table 3 below: 
     
       
         
           
               
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                 Port Identifier 
                   
                   
               
               
                 [Workload ID (IP Address): 
                   
                 Vulnerability 
               
               
                 Port Number] 
                 Vulnerability ID 
                 Score 
               
               
                   
               
             
            
               
                 100.100.1.1: 80 
                 V1 
                 8 
               
               
                 100.100.1.2: 35 
                 V2 
                 4 
               
               
                 100.100.1.3: 80 
                 V1 
                 8 
               
               
                 100.100.1.4: 44 
                 V3 
                 3 
               
               
                   
               
            
           
         
       
     
     The vulnerability exposure scoring module  306  also generates exposure scores for each port  134  based on the permitted connectivity of the port  134  under a particular segmentation policy. For example, in one embodiment, the exposure score for a particular port  134  is based on a count of the number of workloads  138  that can connect to the particular port  134  under the segmentation policy (i.e. the number of edges connected to the workload  138  using the particular port  134  in the segmentation policy graph). The exposure score for a particular port  134  may furthermore be based on permitted connectivity of the port  134  to external networks outside of the administrative domain  150  controlled by the segmentation policy. For example, if the segmentation policy permits a particular port  134  to connect to an external network with a known number of external workloads, a count of the known number of external workloads and a risk factor associated with the external network may contribute to the exposure score to represent the exposure of the port  134  to the external network. If the segmentation policy permits a particular port  134  to connect to an external network with an unknown number of external workloads, a predefined estimated count and risk factor may contribute to the exposure score to represent an estimated exposure of the port  134  based on its connection to the external network. If the external network has a very large number of workloads and/or the external network has a high risk factor (e.g., the external network is the Internet), then the exposure score for the port  134  may be set to a predefined maximum value. 
     In another embodiment, the exposure score for a particular port  134  may be based on a combination of a direct exposure component representing an estimated count of the workloads  138  permitted to connect with the particular port  134  under the segmentation policy, and an indirect exposure component representing a combination of the respective exposure scores of the other ports  134  permitted to directly connect to the particular port  134 . Here, the exposure scores may be generated according to an iterative process. For example, in a first iteration, the direct exposure component may initially be computed for each port  134  and the indirect exposure components may be initialized to zero. Then, in a second iteration, the exposure score for particular port  134  may be computed as a weighted combination of its direct exposure score and the exposure scores associated with each other port  134  permitted to connect to the particular port  134 . This process may be repeated until a stopping criterion is reached (e.g., a predefined number of iterations). 
     In an embodiment, the vulnerability exposure scoring module  306  may generate exposure scores for a particular port according to different parameters. For example, an intra-group exposure score may be computed for a particular port on a particular workload that represents a measure of connectivity of the particular port to other workloads within a limited group of workloads to which the particular workload belongs (e.g., a tier or an application group associated with the particular workload). An inter-group exposure score may be computed for a particular port on a particular workload that represents a measure of connectivity of the particular port to other workloads outside of a limited group of workloads to which the particular workload belongs (e.g., a tier or an application group associated with the particular workload). A total exposure score may be computed for a particular port on a particular workload that represents a measure of connectivity associated with all connections of the particular port to other workloads (e.g., representing a sum of the intra-group exposure score and the inter-group exposure score). In an embodiment, inter-group and intra-group exposure scores may be computed with respect to multiple different groups to generate a set of exposure scores associated with a particular port. For example, for each port, a set of exposure scores may be generated including, for example, (1) an intra-group exposure scores at the tier level; (2) an inter-group exposure score at the tier level; (3) an intra-group exposure score at the application level; (4) an inter-group exposure score at the application level; and (5) a total exposure score. 
     The vulnerability exposure module  306  combines the vulnerability scores associated with each port  134  and the exposure score for each port  134  to generate respective vulnerability exposure scores for each port  134 . For example, in one embodiment, the vulnerability exposure score for a particular port  134  is computed as a product of a function of the exposure score for the particular port  134  and a function of the vulnerability score for the port  134 . For example, in one embodiment, the vulnerability exposure score for a particular port  134  can be computed as:
 
 Ve   P =√{square root over ( E   P )}· V   P   3  
 
where E represents the exposure score for a port P (computed according to any of the methods above), V represents the vulnerability score for the port P, and VE P  represents the vulnerability exposure score for the port P.
 
     The vulnerability exposure scoring module  306  may generate different types of vulnerability exposure scores for a particular port depending on the type of exposure score. For example, an intra-group vulnerability exposure score may be computed for a particular port on a particular workload that represents a measure of risk associated with to connections of the particular port to other workloads within a limited group of workloads in which the particular workload belongs (e.g., a tier or an application group associated with the particular workload). An inter-group vulnerability exposure score may be computed for a particular port on a particular workload that represents a measure of risk associated with connections of the particular port to other workloads outside of a limited group of workloads to which the particular workload belongs (e.g., a tier or an application group associated with the particular workload). A total vulnerability exposure score may be computed for a particular port on a particular workload that represents a measure of risk associated with all connections of the particular port to other workloads (e.g., representing a sum of the intra-group vulnerability exposure score and the inter-group vulnerability exposure score). In an embodiment, inter-group and intra-group vulnerability exposure scores may be computed with respect to multiple different groups to generate a set of exposure scores associated with a particular port. For example, for each port, a set of vulnerability exposure scores may be generated including, for example, (1) an intra-group vulnerability exposure scores at the tier level; (2) an inter-group vulnerability exposure score at the tier level; (3) an intra-group vulnerability exposure score at the application level; (4) an inter-group vulnerability exposure score at the application level; and (5) a total vulnerability exposure score. 
     The exposure score(s), vulnerability score, and vulnerability exposure score(s) for each port  134  may be stored in a table in the vulnerabilities database  356  as illustrated in the example of Table 4: 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 4 
               
               
                   
                   
               
               
                   
                 Port Identifier 
                   
                   
                   
               
               
                   
                 [Workload ID 
                   
                   
                 Vulnerability 
               
               
                   
                 (IP Address): 
                 Exposure 
                 Vulnerability 
                 Exposure 
               
               
                   
                 Port Number] 
                 Score 
                 Score 
                 Score 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 100.100.1.1: 80 
                 25 
                 12 
                 8,640 
               
               
                   
                 100.100.1.2: 35 
                 144 
                 4 
                 768 
               
               
                   
                 100.100.1.3: 80 
                 400 
                 8 
                 10,240 
               
               
                   
                 100.100.1.4: 44 
                 10000 (Max) 
                 3 
                 2,700 
               
               
                   
                   
               
            
           
         
       
     
     For simplicity, Table 4 illustrates a single exposure score and single vulnerability exposure score for each port  134 . As described above, multiple exposure scores and multiple corresponding vulnerability exposure scores may be computed for each port computing according to different parameters. 
     An aggregation module  308  may aggregate data in the vulnerability exposure score table to generate various aggregate data that can be useful to analyze a particular segmentation policy. For example, in one embodiment, the aggregation module  308  may generate port number scores associated with each port number provided by workloads  138  in a particular group (e.g., a tier or application group). Here, the port number score for a particular port number is derived from the vulnerability exposure scores for a particular port number associated with the particular service on all workloads within the group providing the service (e.g., all vulnerability exposure scores associated with port  80  for the workloads within a tier). For example, the port number score may be based on a sum, an average, or a maximum of the vulnerability exposures scores for the port numbers on all workloads  138  within the group. Here, the vulnerability exposure scores used to calculate the port number scores may be inter-group vulnerability exposure scores, intra-group vulnerability exposure scores, total vulnerability exposure scores, or a combination thereof. In one particular example, the aggregation module  308  may generate a list of the services provided by each tier within an application group ranked by their respective port-number scores. This aggregation lets an administrator easily identify which port numbers provide the greatest risk to an administrative domain. 
     The aggregation module  308  may also generate group scores associated with a particular group of workloads  138  such as a tier or application group. Here, the group score for a particular group is derived from the vulnerability exposure scores for all ports  134  on workloads  138  within the particular group. For example, the group score may be based on a sum, an average, a maximum, or another function of the total vulnerability exposures scores for the ports  134  on workloads  138  within the particular group. In another example, the group score may be based on a sum, an average, a maximum, or another function of only the inter-group vulnerability exposure scores for the ports  134  on workloads  138  within the group. In the latter example, the group scores represent a risk associated with connections to workloads  138  outside the group without taking into account the risks associated with connections within the group. These scores may be useful to enable an administrator to easily identify which inter-group connections (e.g., connections between tiers or application groups) provide the greatest risk to an administrative domain. 
     In an embodiment, the aggregation module  308  may generate a visualization of one or more segmentation policy graphs together with various aggregated vulnerability data to provide an administrator with a convenient visualization of the vulnerabilities associated with a particular segmentation strategy.  FIG.  4    illustrates a simple example of a graphical representation of the vulnerability information. In this example, a tier-level segmentation policy graph  405  is illustrated for an application group A having tiers T 1 , T 2 , T 3  and T 4 . Each of the tiers are displayed together with an indication of the number of workloads  138  in each tier (“WLs”) and a group score (“V-E”) for the respective tier, which may be computed according to any of the techniques described above. The aggregation module  308  may furthermore generate a table  410  showing a ranked list of port numbers sorted by their respective port number scores (e.g., from highest to lowest) for the tiers and port numbers in the application group A, which may be computed according to any of the techniques described above 
     Referring again to  FIG.  3   , the rule generation module  310  automatically generates or updates a segmentation policy comprising a set of rules. The particular strategy for generating the rules may be based on configuration settings, the observed traffic graph, the vulnerability exposure scores, or a combination thereof. In general, the rule generation module  310  generates rules that when enforced will allow at least the traffic flows in the traffic flow graph. The rules may also allow traffic flow beyond that specifically observed in the traffic flow graph depending on the level of permissiveness specified in the configuration settings and dependent on the identified vulnerability exposure scores. For example, the rule generation module  310  may generate the most permissive rules allowed by the configuration settings that do not unnecessarily expose an identified vulnerability. Generating rules based on the observed traffic flow graph is beneficial because, assuming that there are no abnormal or malicious communications in the administrative domain  150  in the observed traffic flow graph, the rule generation module  310  can produce a set of rules that permits communications observed during normal operation of the workloads  138  in the administrative domain  150  while blocking or limiting abnormal communications that are potentially malicious. Furthermore, by limiting rules based on the discovered vulnerabilities, the rule generation module  310  may reduce the exposure to a known vulnerability by limiting overly permissive rules. Embodiments of processes for generating rules are further described in U.S. Pat. No. 9,485,279 issued on Nov. 1, 2016 to Paul J. Kirner, et al., which is incorporated by reference herein. 
     The rule generation module  310  may generate rules based on different segmentation strategies depending on configuration parameters. For example, under a port-level granularity segmentation strategy, the rule generation module  310  generates a set of rules that only permits communications between pairs of workloads  138  using the specific ports and protocols observed in the traffic flows. Thus, for example, if the traffic flow module  304  only observes communications between a first workload W 1  and a second workload W 2  using port P, a rule will be generated that permits communications between the first workload W 1  and the second workload W 2  only over port P without permitting communications over other ports. In an embodiment, the generated rule may be specified to apply to particular groups of workloads  138  in which the respective workloads in the pair have memberships. For example, the rule may specified in accordance with respective label sets of the pair of workloads along a predefined set of dimensions (e.g., the dimensions defining a tier). As a result, the rule will also permit communications conforming to the specified ports and protocols between different pairs of workloads that conform to the same respective label sets along the same predefined set of dimensions (e.g., the same respective tiers) as the observed pair of workloads. For example, a rule may be generated that permits workloads  138  in a first tier associated with the label set “App: Point of Sale; Environment: PCI; Role: Database” to provide a service on port  5432  using TCP protocol to workloads  138  in a second tier associated with the label set “App: Point of Sale: Environment: PCI; Role: Processing.” 
     In a workload-level granularity segmentation strategy, the rule generation module  310  generates rules that enable communications between groups of workloads  138  that are observed as being connected in the traffic flow graph, without limiting the rules to specific ports or protocols. For example, if a connection is observed between a workload  138  in a first group of workloads  138  and a workload  138  in a second group of workloads  138 , a rule is generated to permit communications between workloads  138  in the first group and workloads in the second group. Here, the group to which the rule generating applies may be preconfigured and may be based on a label set along a predefined set of dimensions. For example, under one configuration, this strategy may generate a rule may that permits workloads  138  in a first tier associated with the label set “App: Point of Sale; Environment: PCI; Role: Database” to provide any service (using any port and any protocol) to workloads  138  in a second tier associated with the label set “App: Point of Sale: Environment: PCI; Role: Processing” if any traffic flows are observed between the first and second tier in the traffic flow graph. Upon enforcement of the segmentation policy, communications between pairs of workloads that are not expressly permitted by the rules will be blocked. 
     Under other configuration settings, the rule generation module  310  may generate rules that permit communications between certain specified groups of workloads  138  (e.g., based on the label sets) independently of the observed traffic flows. For example, in a group-level granularity segmentation strategy, the rule generation module  310  generates a set of rules that permits communications between all workloads  135  in a predefined group (e.g., share a set of labels along a predefined set of dimensions) without regard to observed communications. For example, the rule generation module  310  may generate rules that permit communications between all workloads  138  within the same application group. For example, a rule may be generated that permits workloads  138  in an application group associated with the label set “App: Point of Sale; Environment: PCI” to provide any service (using any port and any protocol) to other workloads  138  in the application group. Upon enforcement of the segmentation policy, communications between pairs of workloads that are not expressly permitted by the rules will be blocked. 
     In another embodiment, configuration settings may cause the rule generation module  310  to generate rules permitting communications between specified groups of workloads  138 . For example, under certain configuration settings, the rule generation module  310  may generate rules permitting communications between a first application group A 1  and a second application group A 2 . 
     In an embodiment, rules may be generated differently for different groups of workloads  138  by specifying different configuration settings for different groups. For example, rules may be generated for workloads  138  in a first application group according to a workload-level granularity segmentation strategy while rules may be generated for workloads  138  in a second application group according to a port-level granularity segmentation strategy. Furthermore, rules controlling communications between different groups of workloads  138  may be generated according to different configuration settings. For example, rules controlling communications between workloads  138  in a first application group and workloads  138  in a second application group may be generated according to a workload-level granularity segmentation strategy while rules controlling communications between workloads  138  in a first application group and workloads  138  in a third application group may be generated according to a group-level granularity segmentation strategy. 
     In other embodiments, a segmentation strategy may be applied to generate rules in which workloads  138  are permitted to provide services according to a first segmentation strategy and are permitted to use services according to second segmentation strategy. For example, a segmentation strategy may generate rules that enable workloads  138  to provide services to any workloads  138  within an application group without regard to specific port or protocol (e.g., consistent with a group-level granularity segmentation strategy), but only enables workloads  138  to use services consistent with the ports and protocols in the observed traffic graph (consistent with a port-level granularity segmentation strategy). 
     In yet other embodiments, other variations of segmentation strategies or combinations thereof may be applied that do not necessarily conform to the port-level granularity, workload-level granularity, or group-level granularity strategies described above or the variations thereof discussed above. 
     The rule generation module  310  may modify an initial segmentation strategy based on the vulnerability exposure scores to reduce the number of permitted connections that may expose the administrative domain  150  to a vulnerability. Here, the rule generation module  310  identifies vulnerable ports that have vulnerability exposure scores exceeding a predefined threshold score. If a resulting segmentation policy enables communication over a vulnerable port, the segmentation strategy may be modified so that the resulting segmentation policy limits the permitted communications on the vulnerable port based on the observed traffic flow graph, as will be described in further detail below with reference to  FIGS.  5 - 6   . The vulnerability exposure scores may then be updated based on the modified segmentation strategy to enable an administrator to compare the different segmentation options. 
     The instruction distribution module  312  generates the management instructions from the rules for a current segmentation policy and distributes the relevant management instructions to the OS instances  130  as described above. In an embodiment, the instruction distribution module  312  generates and distributes the relevant management instructions to the OS instances  130  upon approval from an administrator. Alternatively, the instruction distribution module  312  may automatically distribute the instructions upon being generated without necessarily requiring an additional approval. 
       FIG.  5    illustrates a first example of a technique for modifying a segmentation strategy based on detected vulnerabilities. Here, an initial segmentation policy (as may be configured by an administrator according to the configuration setting) that would result from an initial segmentation strategy is represented by an initial segmentation policy graph  502 . In this example, the initial segmentation policy graph  502  includes a rule that specifies that all workloads  138  in an application group A can communicate with each other over all ports and protocols (i.e., a group-level granularity segmentation strategy). A vulnerable port having a port number P is identified on at least one workload  138  in a tier T 1  in the application group A. The observed traffic flow graph  504  indicates that the workload in tier T 1  provides the service using the port number P to one or more workloads  138  only in tier T 2 , but does not use the port number P in communications with workloads  138  in tiers T 3  or T 4 . The segmentation strategy may be modified to generate a segmentation policy that only permits the workloads in the tier T 1  to provide the service using the port number P to workloads  138  in tier T 2 , without permitting the workloads  138  in tier T 1  to provide the service using the port number P to workloads  138  in tiers T 3  or T 4 . The modified segmentation strategy may generate a segmentation policy that retains rules permitting communications unaffected by the vulnerability (e.g., communications between tier T 3  and T 4 ). The modified segmentation policy is represented by a modified segmentation policy graph  506 . Thus, in this example, the modified segmentation policy still permits the observed communication over the vulnerable port, but limits the workloads  138  to which the vulnerable port can connect, thereby reducing overall exposure of the administrative domain to the vulnerability. 
       FIG.  6    illustrates a second example of a technique for modifying a segmentation strategy based on detected vulnerabilities. Here, an initial segmentation strategy (as may be configured by an administrator according to the configuration setting) that would result from an initial segmentation strategy is represented by an initial segmentation policy graph  602 . In this example, the initial segmentation policy specifies that workloads  138  in an application group A can communicate with each other for all services (i.e., a group-level granularity segmentation strategy). A vulnerable port having a port number P 1  is identified on one or more workloads  138  in a tier T 1  in the application group A. In this case, the observed traffic flow graph  604  indicates that the workloads  138  in tier T 1  do not communicate to any tiers using the vulnerable port number P 1 , but instead communicate using port number P 2  to workloads  138  in tiers T 2 , T 4  and communicate using port number P 3  to workloads  138  in tier T 3 . The initial segmentation strategy may be modified to generate a segmentation policy that permits workloads  138  in tier T 1  to communicate using only port numbers P 2  and P 3  consistent with the observed traffic flow graph, thus excluding traffic over the vulnerable port number P 1 , which was not utilized in the traffic flow graph. Thus, as illustrated in the modified segmentation policy graph  606 , the workloads  138  in tier T 1  are permitted to communicate using port number P 3  to workloads  138  in tier T 3  and may communicate using port number P 2  to workloads  138  in tiers T 2  and T 3 . The modified segmentation policy may also still permit communications unaffected by the vulnerability (e.g., communications between tier T 3  and T 4 ) without modification. Thus, the modified segmentation policy still permits communications from tier T 1  to all workloads  138  in the application group A consistent with the original segmentation strategy, but limits the communications to utilizing the specific ports in the observed traffic flow graph, thereby reducing overall exposure of the administrative domain to the vulnerable port. 
     In an embodiment, an administrator interface may enable an administrator to select a segmentation strategy from a predefined set of segmentation strategies (e.g., port-level granularity, work-level granularity, or group-level granularity), and may also enable the administrator to toggle on or off the option to modify the strategy to reduce vulnerabilities. The administrator interface may present vulnerability information associated with the different possible segmentation strategies in order to enable the administrator to best assess the desired segmentation strategy for the administrative domain  150 . 
       FIG.  7    is a flowchart illustrating an example embodiment of a process for generating vulnerability exposure scores associated with ports  134  on workloads  138  under a particular segmentation policy. The segmentation server  120  obtains  702  a segmentation policy. The segmentation server  120  furthermore obtains  704  detected vulnerabilities associated with ports  134  on the workloads  138  in the administrative domain  150  (e.g., by performing vulnerability scans on the workloads  138 ) and vulnerability scores associated with each of the detected vulnerabilities. The segmentation server  120  generates  706  exposure scores associated with each of the ports  134  based on the segmentation policy. The exposure scores represent a measure of permitted connectivity for the workloads  138  in the administrative domain  150  and may include one or more of total exposure scores, intra-group exposure scores associated with one or more groups, and inter-group exposure scores associated with one or more groups as described above. The segmentation server  120  combines  708  the respective vulnerability scores and respective exposure scores associated with the ports  134  to generate vulnerability exposure scores for each respective port  134 . The vulnerability exposure scores may include one or more of total vulnerability exposure scores, intra-group vulnerability exposure scores associated with one or more groups, and inter-group vulnerability exposure scores associated with one or more groups as described above. 
       FIG.  8    is a flowchart illustrating an example embodiment of a process for aggregating vulnerability exposure scores to generate a presentation of vulnerability exposure information. The segmentation server  120  obtains  802  vulnerability exposure scores associated with each port  134  on workloads  138  operating in an administrative domain  150 . The segmentation server  120  aggregates  804  the vulnerability exposure scores to generate aggregate vulnerability exposure information. Depending on configuration settings or user requests, the segmentation  120  may aggregate the vulnerability scores in different ways. For example, the segmentation server  120  may generate port number scores by combining vulnerability exposures scores associated with a particular port number for all workloads within  138  a tier or other predefined group. Furthermore, the segmentation server  120  may generate group level scores by combining vulnerability scores associated with all workloads  138  in a tier or other predefined group across all port numbers. The segmentation server  120  then generates  806  a presentation of the aggregate vulnerability exposure information (e.g., as illustrated in  FIG.  4    described above). The segmentation server  120  outputs  808  the presentation (e.g., via a web interface) to enable an administrator to view and interact with the vulnerability exposure information. 
       FIG.  9    is a flowchart illustrating an example embodiment of a process for generating a segmentation policy based on vulnerability exposure scores. The segmentation server  120  obtains  902  vulnerability exposure scores associated with each port  134  on workloads  138  within an administrative domain  150 . The segmentation server  120  observes  904  communications between the workloads  138  under an initial segmentation policy to generate a traffic flow graph. In an embodiment, the initial segmentation policy applied while generating the traffic flow graph may permit all workloads  138  to communicate with any other workloads  138  on all ports. Alternatively, the initial segmentation policy may be more restrictive. The segmentation server  120  generates  906  a segmentation policy based on the vulnerability exposures, the traffic flow graph, and configuration settings. Here, the segmentation server  120  may generate a segmentation policy that generally conforms to the strategy specified in the configuration settings based on the observed traffic flow graph, but includes one or more changes to the rules that will reduce exposure associated with one or more vulnerabilities. For example, the segmentation server  120  may detect a vulnerable port on a workload in a first group of workloads (e.g., a first tier T 1 ). The segmentation server  120  may furthermore determine that the first group of workloads is connected to a second group of workloads (e.g., a second tier T 2 ) in the traffic flow graph, while determining that the first group of workloads is not connected to a third group of workloads (e.g., a third tier T 3 ) in the traffic flow graph using the vulnerable port even though such a connection would be permissible under an initial segmentation policy. In this case, the segmentation server  120  may generate a modified segmentation policy that permits the first group of workloads T 1  to communicate with the second group of workloads T 2  without permitting communication between the first group of workloads T 1  and the third group of workloads T 3 . In another example, the segmentation server  120  may detect a vulnerable port on a workload in a first group of workloads T 1 . Furthermore, the segmentation server  120  may detect a lack of connectivity using between the first group of workloads T 1  and the second group of workloads T 2  using the vulnerable port (although such a connection would be permissible under the initial segmentation policy), but instead detects connectivity using one or more non-vulnerable ports between the first group of workloads T 1  and the second group of workloads T 2 . In this case, the segmentation server  120  may generate a modified segmentation policy that permits communications between the first group of workloads T 1  and the second group of workloads T 2  over the non-vulnerable ports used in the traffic flow graph without permitting communication over the vulnerable port that was not utilized in the traffic flow graph. The segmentation server  120  generates  908  management instructions based on the segmentation policy and sends  910  the management instructions to OS instances  130  to enforce the segmentation policy. 
     Beneficially, the above described techniques enable automatic generation and presentation of analytical data assessing vulnerabilities of workloads  138  in an administrative domain  150  and a measure of the exposure to those vulnerabilities associated with a particular segmentation policy. This enables an administrator to easily evaluate different segmentation strategies and assess the risks associated with them. Moreover, the segmentation server  120  can beneficially automatically generate a segmentation policy that is generally consistent with a desired segmentation strategy but is modified to reduce exposure to certain vulnerabilities without impeding operation of the workloads  138 . Upon modified the segmentation policy, the vulnerability exposure scores may be recalculated and presented to enable an administrator to compare the effects of the different segmentation policies. Thus, the segmentation server  120  enables the workloads  150  in the administrative domain  150  to operate with improved security. 
     The foregoing description of the embodiments of the invention has been presented for the purpose of illustration; it is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Persons skilled in the relevant art can appreciate that many modifications and variations are possible in light of the above disclosure. 
     Some portions of this description describe the embodiments of the invention in terms of algorithms and symbolic representations of operations on information. These algorithmic descriptions and representations are commonly used by those skilled in the data processing arts to convey the substance of their work effectively to others skilled in the art. These operations, while described functionally, computationally, or logically, are understood to be implemented by computer programs or equivalent electrical circuits, microcode, or the like. Furthermore, it has also proven convenient at times, to refer to these arrangements of operations as modules, without loss of generality. The described operations and their associated modules may be embodied in software, firmware, hardware, or any combinations thereof. 
     Any of the steps, operations, or processes described herein may be performed or implemented with one or more hardware or software modules, alone or in combination with other devices. In one embodiment, a software module is implemented with a computer program product comprising a computer-readable medium containing computer program code, which can be executed by a computer processor for performing any or all of the steps, operations, or processes described. 
     Embodiments of the invention may also relate to an apparatus for performing the operations herein. This apparatus may be specially constructed for the required purposes, and/or it may comprise a general-purpose computing device selectively activated or reconfigured by a computer program stored in the computer. Such a computer program may be stored in a tangible computer readable storage medium or any type of media suitable for storing electronic instructions, and coupled to a computer system bus. Furthermore, any computing systems referred to in the specification may include a single processor or may be architectures employing multiple processor designs for increased computing capability. 
     Finally, the language used in the specification has been principally selected for readability and instructional purposes, and it may not have been selected to delineate or circumscribe the inventive subject matter. It is therefore intended that the scope of the invention be limited not by this detailed description, but rather by any claims that issue on an application based hereon. Accordingly, the disclosure of the embodiments of the invention is intended to be illustrative, but not limiting, of the scope of the invention, which is set forth in the following claims.