# Patent

## Title
System and method for redirected firewall discovery in a network environment

## Abstract

A method is provided in one example embodiment that includes receiving metadata from a host over a metadata channel. The metadata may be correlated with a network flow and a network policy may be applied to the connection. In other embodiments, a network flow may be received from a host without metadata associated with the flow, and a discovery redirect may be sent to the host. Metadata may then be received and correlated with the flow to identify a network policy action to apply to the flow.

## Background
RELATED APPLICATION
This Application is a continuation (and claims the benefit of priority under 35 U.S.C. § 120) of U.S. application Ser. No. 14/263,164, filed Apr. 28, 2014, entitled “SYSTEM AND METHOD FOR REDIRECTED FIREWALL DISCOVERY IN A NETWORK ENVIRONMENT,” Inventors Geoffrey Cooper et al., which is a continuation (and claims the benefit of priority under 35 U.S.C. § 120) of U.S. application Ser. No. 13/275,249, filed Oct. 17, 2011, now issued as U.S. Pat. No. 8,713,668, entitled “SYSTEM AND METHOD FOR REDIRECTED FIREWALL DISCOVERY IN A NETWORK ENVIRONMENT,” Inventors Geoffrey Cooper et al. The disclosures of both of the prior applications are considered part of (and are incorporated by reference in) the disclosure of this application.


TECHNICAL FIELD
This specification relates in general to the field of network security, and more particularly, to a system and method for redirected firewall discovery in a network environment.
BACKGROUND
The field of network security has become increasingly important in today's society. The Internet has enabled interconnection of different computer networks all over the world. However, the Internet has also presented many opportunities for malicious operators to exploit these networks. Certain types of malicious software (e.g., bots) can be configured to receive commands from a remote operator once the software has infected a host computer. The software can be instructed to perform any number of malicious actions, such as sending out spam or malicious emails from the host computer, stealing sensitive information from a business or individual associated with the host computer, propagating to other host computers, and/or assisting with distributed denial of service attacks. In addition, the malicious operator can sell or otherwise give access to other malicious operators, thereby escalating the exploitation of the host computers. Thus, the ability to effectively protect and maintain stable computers and systems continues to present significant challenges for component manufacturers, system designers, and network operators.



BRIEF DESCRIPTION OF THE DRAWINGS
To provide a more complete understanding of the present disclosure and features and advantages thereof, reference is made to the following description, taken in conjunction with the accompanying figures, wherein like reference numerals represent like parts, in which:
FIG. 1 is a simplified block diagram illustrating an example embodiment of a network environment in which a firewall may be discovered through host redirection according to this specification;
FIG. 2 is simplified block diagram illustrating additional details that may be associated with one potential embodiment of the network environment;
FIG. 3 is a simplified interaction diagram illustrating potential operations that may be associated with example embodiments of the network environment;
FIG. 4 is a simplified interaction diagram illustrating potential operations that may be associated with example embodiments of the network environment with a stale firewall cache that identifies an invalid firewall for a managed route;
FIG. 5 is a simplified interaction diagram illustrating potential operations that may be associated with other example embodiments of the network environment with a stale firewall cache that identifies an invalid firewall for a managed route; and
FIG. 6 is an example packet data unit format that may be associated with exchanging metadata in example embodiments of the network environment.



DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS
Overview
A method is provided in one example embodiment that includes receiving metadata from a host over a metadata channel. The metadata may be correlated with a network flow and a network policy may be applied to the flow.
In other embodiments, a network flow may be received from a host without metadata associated with the flow, and a discovery redirect may be sent to the host. Metadata may then be received and correlated with the flow to identify a network policy action to apply to the flow.
Example Embodiments
Turning to FIG. 1, FIG. 1 is a simplified block diagram of an example embodiment of a network environment 10 in which a firewall may be discovered through host redirection. In the embodiment illustrated in FIG. 1, network environment 10 can include Internet 15, user hosts 20a and 20b, a firewall 25, a policy server 30, a mail server 35, and a web server 40. In general, user hosts 20a-20b may be any type of termination node in a network connection, including but not limited to a desktop computer, a server, a laptop, a mobile telephone, or any other type of device that can receive or establish a connection with another node, such as mail server 35 or web server 40. Firewall 25 may control communications between user hosts 20a-20b and other nodes attached to Internet 15 or another network, such as by blocking unauthorized access while permitting authorized communications. In some instances, firewall 25 may be coupled to or integrated with an intrusion prevention system, network access control device, web gateway, email gateway, or any other type of gateway between Internet 15 and user hosts 20a-20b. Moreover, the location of firewall 25 in the routing topology close to user hosts 20a-20b is arbitrary. Policy server 30 may be coupled to or integrated with firewall 25, and may be used to manage user hosts 20a-20b and to administer and distribute network policies. Thus, in this example embodiment, user hosts 20a-20b may communicate with servers attached to Internet 15, such as mail server 35 or web server 40, by establishing a connection through firewall 25 if permitted by policies implemented in firewall 25 and managed by policy server 30.
Each of the elements of FIG. 1 may couple to one another through simple interfaces or through any other suitable connection (wired or wireless), which provides a viable pathway for network communications. Additionally, any one or more of these elements may be combined or removed from the architecture based on particular configuration needs. Network environment 10 may include a configuration capable of transmission control protocol/Internet protocol (TCP/IP) communications for the transmission or reception of packets in a network. Network environment 10 may also operate in conjunction with a user datagram protocol/IP (UDP/IP) or any other suitable protocol where appropriate and based on particular needs.
For purposes of illustrating the techniques for providing network security in example embodiments, it is important to understand the activities occurring within a given network. The following foundational information may be viewed as a basis from which the present disclosure may be properly explained. Such information is offered earnestly for purposes of explanation only and, accordingly, should not be construed in any way to limit the broad scope of the present disclosure and its potential applications.
Typical network environments used in organizations and by individuals include the ability to communicate electronically with other networks using the Internet, for example, to access web pages hosted on servers connected to the Internet, to send or receive electronic mail (i.e., email) messages, or to exchange files. However, malicious users continue to develop new tactics for using the Internet to spread malware and to gain access to confidential information. Malware generally includes any software designed to access and/or control a computer without the informed consent of the computer owner, and is most commonly used as a label for any hostile, intrusive, or annoying software such as a computer virus, bot, spyware, adware, etc. Once compromised, malware may subvert a host and use it for malicious activity, such as spamming or information theft. Malware also typically includes one or more propagation vectors that enable it to spread within an organization's network or across other networks to other organizations or individuals. Common propagation vectors include exploiting known vulnerabilities on hosts within the local network and sending emails having a malicious program attached or providing malicious links within the emails.
One way in which malware may operate is to deceive a user by using a different network protocol exchange than the user expects. The malware may be packaged so as to convince the user to allow access to run it in some innocuous way, thus allowing it access to the network, which often may require passing through a firewall or other security measure. The malware may then exploit the access to engage in alternative or additional activities not contemplated by the user. For example, a game may send email messages or a word processor may open a web connection. At the same time, the malware may also use standard protocols to deceive the firewall into permitting the malware to establish remote connections.
Botnets, for example, use malware and are an increasing threat to computer security. In many cases they employ sophisticated attack schemes that include a combination of well-known and new vulnerabilities. Botnets generally use a client-server architecture where a type of malicious software (i.e., a bot) is placed on a host computer and communicates with a command and control (C&C) server, which may be controlled by a malicious user (e.g., a botnet operator). Usually, a botnet is composed of a large number of bots that are controlled by the operator using a C&C protocol through various channels, including Internet Relay Chat (IRC) and peer-to-peer (P2P) communication. The bot may receive commands from the C&C server to perform particular malicious activities and, accordingly, may execute such commands. The bot may also send any results or pilfered information back to the C&C server.
A bot is often designed to initiate communication with the C&C server and to masquerade as normal web browser traffic. For example, a bot may use a port typically used to communicate with a web server. Such bots, therefore, may not be detected by existing technologies without performing more detailed packet inspection of the web traffic. Moreover, once a bot is discovered, the botnet operator may simply find another way to masquerade network traffic by the bot to continue to present as normal web traffic. More recently, botnet operators have crafted bots to use encryption protocols such as, for example, secure socket layer (SSL), thereby encrypting malicious network traffic. Such encrypted traffic may use a Hypertext Transfer Protocol Secure (HTTPS) port so that only the endpoints involved in the encrypted session can decrypt the data. Thus, existing firewalls and other network intrusion prevention technologies may be unable to perform any meaningful inspection of the web traffic, and bots may continue to infect host computers within networks.
Other software security technology focused on preventing unauthorized program files from executing on a host computer may have undesirable side effects for end users or employees of a business or other organizational entity. Network or Information Technology (IT) administrators may be charged with crafting extensive policies relevant to all facets of the business entity to enable employees to obtain software and other electronic data from desirable and trusted network resources. Without extensive policies in place, employees may be prevented from downloading software and other electronic data from network resources that are not specifically authorized, even if such software and other data facilitate legitimate and necessary business activities. Such systems may be so restrictive that if unauthorized software is found on a host computer, any host computer activities may be suspended pending network administrator intervention. Moreover, at the network level there may simply be too many applications to effectively track and incorporate into policies. Large whitelists or blacklists can be difficult to maintain and may degrade network performance, and some applications may not be susceptible to easy identification.
Information may be shared between a host and a firewall to collectively and mutually achieve better security, though. For example, a host may understand an application as an executable file that is running a process with specific authentication, while the firewall may understand the application as a protocol in a TCP connection, which may also be correlated to a particular user authentication. The host may share session descriptors and other metadata with the firewall, and the firewall may share network policy with the host as needed to correlate application activities with expected network behavior. Network policy may include elements of security policy as well as other network specific parameters, such as quality of service (QoS) and routing. A host may also be associated with a universally unique identifier (UUID), which can be used to correlate connections and activities originating behind network address translators.
A host may also notify the firewall of additional network connections to the host. If a host has both wireless and wired connections active simultaneously, for example, there may be a risk of data received on one connection being transmitted on the other, so it may be desirable to restrict access to sensitive data. A host may also notify the firewall if the connection is associated with a virtual machine, or if the host has mountable read/write media, such as a USB stick attached.
In some embodiments of network environment 10, a host may include multiple attachment points, causing it to have multiple IP addresses. In other embodiments, a host may use the IP version 6 (IPv6), perhaps including Privacy Extensions (RFC4941), causing it to have one or more registered and known IPv6 addresses and one or more hidden or private IPv6 addresses. In these embodiments, an interlocked firewall may readily use dynamic information sharing to discover the user-to-host mapping for all the addresses on a host.
This dynamic information sharing between an interlocked host and firewall in network environment 10 may provide several benefits over conventional architectures. For example, by coordinating firewall policy with a host, a firewall can manage routes differently, such as by allowing or denying traffic depending on which of multiple users on a host may be attempting to establish a connection. Moreover, only applications that may need to be granularly controlled need to be controlled by the firewall. Thus, the firewall may control arbitrary or evasive applications, provide higher effective throughput, and control mobile-user traffic. In addition, traffic that does not need to be completely allowed or denied can be rate-limited. Arbitrary or evasive applications can also be rate-limited with process information available on a firewall, and differentiated services can be provided for managed and unmanaged hosts.
Many hosts may only use a single firewall for all routes. An agent running on a host may maintain a firewall cache that can identify this firewall. In a more complex scenario, a host may use more than one firewall, in which case it is important that the host understand which firewall will process a given flow. The firewall cache can provide routes through more than one firewall by mapping a given network route to a particular firewall. Routes are generally managed or unmanaged. A “managed route” generally refers to a route through a firewall that may be configured to accept metadata for network flows, while an “unmanaged route” is a route through a firewall that may not accept metadata. A firewall cache may associate a network (e.g., identified by a network destination and network mask) with a firewall designated for managing flows to the network, for example, or may associate an unmanaged route to a null value. The firewall cache may be initialized or configured by an administrator, providing separate configurations for each named network and/or default configurations for the first time a network is used. Some configurations may define one firewall for Internet addresses, initially based on an assumption that all global IP addresses are on the Internet.
Session descriptors generally include information about a host and an application associated with a given network session. For example, a session descriptor may include a UUID associated with the host and the user credentials of a process owner. Since a user can run separate processes with different user credentials, such information may be particularly advantageous for Citrix and terminal services. A session descriptor may additionally include a filename, pathname or other unique identifier of an application file (e.g., C:\...\WINWORD.EXE) that is running the process attempting to establish a network connection. For example, in some embodiments the application may be identified by a hash function of the application's executable file, so as to make it more difficult for a malicious user to spoof the application name. A firewall may correlate this information with an application identifier or protocol to ensure that the application is performing as expected. A session descriptor may also contain information about the host environment, such as software installed on the host and the current configuration and state of the software, permitting the firewall to act as a network access control device. For example, a session descriptor may indicate whether the local anti-virus system is up to date and running. If Host-based Data Loss Prevention (HDLP) software is available, a session descriptor may also include file-typing information for file transfer. HDLP normally determines the type of file being transmitted out of the network (e.g., PDF, Word, etc.). The firewall may have additional policies about certain file types being transmitted over particular protocols, which may not be visible directly to an HDLP program.
Session descriptors and other metadata may be exchanged over an out-of-band communication channel (a “metadata channel”) in some embodiments of network environment 10, which may be implemented with a protocol that provides authentication and/or encryption for communication privacy. In more particular embodiments, a Datagram Transport Layer Security (DTLS) protocol may be used to provide a metadata channel with communication privacy, and a host and a firewall may use certificates based on a common certificate authority. A policy server may distribute certificates to a host and firewall in some embodiments, while an external certificate authority may be used in other embodiments. Some protocols, including DTLS, may also be used to establish a back channel from a firewall to a host, which may be used for error messages and diagnostics, for example.
A host can send metadata to a firewall before opening a new network flow such that, in general, metadata arrives at the firewall before the first packet of a new flow. More particularly, a firewall agent on the host may intercept the first packet of a new flow and send a session descriptor and other metadata associated with the flow, such as source IP address and port, destination IP address and port, and protocol. The firewall may maintain a metadata cache and correlate a network flow with metadata if the firewall agent releases the flow. More particularly, the firewall may correlate metadata with network flow data, which broadly refers to information that associates a given network flow with a source node (i.e., a node sending or attempting to send a packet) and a destination node (i.e., a node to which a packet is addressed) or destination nodes (e.g., broadcast or multicast address). Flow data may also include other information about the flow, such as a protocol family or protocol, for example.
For example, TCP generally opens a new flow (generally referred to as a “connection” in the context of a TCP flow) with a handshake—a host sends a first packet with one of the TCP flag bits (i.e., the SYN bit) set to indicate that a three-way handshake is in progress. Thus, an agent on a source node may intercept a new TCP connection by detecting an application on the source node sending a SYN packet (i.e., a packet with the SYN bit set) and holding the SYN packet. The agent may be able to identify a firewall for managing the route to a destination node associated with the new connection, such as by locating the route and its associated firewall in a firewall cache, and send metadata to the firewall (which the firewall can cache) over a secure metadata channel. The connection request may then be released by sending the SYN packet to the firewall, and the firewall may correlate the source IP, destination IP, protocol, etc.
Flows are not limited to communications using a reliable protocol such as TCP; a flow may also include communications using an unreliable protocol such as UDP or IP. In other embodiments, an agent may track flows that use an unreliable protocol and intercept a new flow by holding the first packet of a flow while it transmits metadata. The agent may also be able to retransmit the metadata by caching a hash of the first packet of a flow and comparing the hash to the hash of subsequent packets to determine if the first packet is being retransmitted by an application. In yet other embodiments, a firewall may track flows and cache the first packet until metadata arrives. In still yet other embodiments, metadata may be sent with every packet in a flow using an unreliable protocol, or never sent. Caches of first packet data can be very short-lived (e.g. less than one second to five seconds).
However, a host may not always be able to identify or locate such a firewall. For example, a host may move from one network to another (e.g., a laptop moving from a home network to a corporate network), may have a misconfigured routing table, a stale table entry, or a missing table entry, which may cause the host to send metadata to the incorrect firewall (or send no metadata at all). If a host cannot determine the location of a firewall, an additional mechanism is needed.
In accordance with embodiments disclosed herein, network environment 10 may provide a system and method for redirection-based discovery of an interlocked firewall. A firewall can maintain a list of managed hosts, which may be identified within a given subnet range or identified explicitly by IP address or hostname, for example. In some embodiments, a policy server may provide the list to a firewall. The firewall may cache or drop the initial connection packet (e.g., a SYN packet) and send a firewall-host discovery redirect to any managed host that attempts to open a connection without sending appropriate metadata. In more particular embodiments, network environment 10 can decrease redirect traffic volume by not sending discovery redirects for local link or local broadcasts (e.g., netbios probes on port 137).
Managed hosts and firewalls may also maintain a shared secret (e.g., a password, key, etc.) for authentication of redirect packets. The shared secret may be distributed by a policy server or manually configured, for example, and a firewall may share the same secret with more than one host, including all hosts within a site. In certain embodiments, the shared secret may be a function of time. In yet other embodiments, managed hosts and firewalls may use asymmetric key cryptography (i.e., public key cryptography) to secure redirect packets.
In more particular embodiments, a discovery redirect may be implemented in an Internet Control Message Protocol (ICMP) packet, such as an ICMP Destination Unreachable (DU) packet for administratively prohibited communications (i.e., ICMP type 3, code 13). An ICMP DU packet may include the IP header and TCP (or UDP) headers of the original packet, and may further include a magic number and a hash-based message authentication code (HMAC). In such an embodiment, the magic number may be a 32-bit identifier (e.g., 0x46484131 or “FHA1”), which may also act as a protocol version number. In general, an HMAC is a message authentication code (MAC) involving a cryptographic hash function in combination with a shared secret (e.g., a secret key). A MAC (and an HMAC) may be used to simultaneously verify both the data integrity and the authenticity of a message. An HMAC may include, for example, the host-firewall shared secret, source IP address, destination IP address, IP identification, firewall IP address, and TCP initial sequence number.
In other embodiments, a firewall may have a public/private key pair that it can use to establish a metadata channel (e.g., a DTLS connection). The firewall's private key may be used to encrypt a hash of the discovery redirect packet (using RSA for example). The encrypted hash can be inserted into the discovery redirect, and a host can validate the discovery redirect by decrypting the hash using the firewall's public key. For example, an ICMP DU packet may be used as described above, but replacing the HMAC with the encrypted hash.
While a host may ignore most of these types of ICMP DU packets, the host can take appropriate action when it receives a discovery redirect packet with an HMAC or encrypted hash. For example, a host may calculate an HMAC using its shared key and authenticate the message by comparing the calculated HMAC to the HMAC received in the discovery redirect packet. If the message is authentic, a host may update its firewall cache to reflect the firewall information in the discovery redirect packet and send metadata to the firewall for the given connection.
Turning to FIG. 2, FIG. 2 is a simplified block diagram illustrating additional details that may be associated with potential embodiments of network environment 10. FIG. 2 includes Internet 15, user host 20a, firewall 25, and a server 45. Each of user host 20a and firewall 25 may include a respective processor 50a-50b, a respective memory element 55a-55b, and various hardware and/or software modules. More particularly, user host 20a may include an application 60, a configuration database 65, a client certificate 70, and a firewall agent 75, which may maintain a firewall cache 77. Firewall 25 may include a host manager 80 and a policy module 85, as well as a log 90, a metadata cache 95, and a server certificate 97.
In one example implementation, user hosts 20a-20b, firewall 25, and/or policy server 30 are network elements, which are meant to encompass network appliances, servers, routers, switches, gateways, bridges, loadbalancers, processors, modules, or any other suitable device, component, element, or object operable to exchange information in a network environment. Network elements may include any suitable hardware, software, components, modules, or objects that facilitate the operations thereof, as well as suitable interfaces for receiving, transmitting, and/or otherwise communicating data or information in a network environment. This may be inclusive of appropriate algorithms and communication protocols that allow for the effective exchange of data or information. However, user hosts 20a-20b may be distinguished from other network elements, as they tend to serve as a terminal point for a network connection, in contrast to a gateway or router that tends to serve as an intermediate point in a network connection. User hosts 20a-20b may also be representative of wireless network nodes, such as an i-Phone, i-Pad, Android phone, or other similar telecommunications devices.
In regards to the internal structure associated with network environment 10, each of user hosts 20a-20b, firewall 25, and/or policy server 30 can include memory elements for storing information to be used in the operations outlined herein. Each of user hosts 20a-20b, firewall 25, and/or policy server 30 may keep information in any suitable memory element (e.g., random access memory (RAM), read-only memory (ROM), erasable programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), application specific integrated circuit (ASIC), etc.), software, hardware, or in any other suitable component, device, element, or object where appropriate and based on particular needs. Any of the memory items discussed herein (e.g., memory elements 55a-55b) should be construed as being encompassed within the broad term ‘memory element.’ The information being used, tracked, sent, or received by user hosts 20a-20b, firewall 25, and/or policy server 30 could be provided in any database, register, queue, table, cache, control list, or other storage structure, all of which can be referenced at any suitable timeframe. Any such storage options may be included within the broad term ‘memory element’ as used herein.
In certain example implementations, the functions outlined herein may be implemented by logic encoded in one or more tangible media (e.g., embedded logic provided in an ASIC, digital signal processor (DSP) instructions, software (potentially inclusive of object code and source code) to be executed by a processor, or other similar machine, etc.), which may be inclusive of non-transitory media. In some of these instances, memory elements (as shown in FIG. 2) can store data used for the operations described herein. This includes the memory elements being able to store software, logic, code, or processor instructions that are executed to carry out the activities described herein.
In one example implementation, user hosts 20a-20b, firewall 25, and/or policy server 30 may include software modules (e.g., firewall agent 75 and/or host manager 80) to achieve, or to foster, operations as outlined herein. In other embodiments, such operations may be carried out by hardware, implemented externally to these elements, or included in some other network device to achieve the intended functionality. Alternatively, these elements may include software (or reciprocating software) that can coordinate in order to achieve the operations, as outlined herein. In still other embodiments, one or all of these devices may include any suitable algorithms, hardware, software, components, modules, interfaces, or objects that facilitate the operations thereof.
Additionally, each of user hosts 20a-20b, firewall 25, and/or policy server 30 may include a processor that can execute software or an algorithm to perform activities as discussed herein. A processor can execute any type of instructions associated with the data to achieve the operations detailed herein. In one example, the processors (as shown in FIG. 2) could transform an element or an article (e.g., data) from one state or thing to another state or thing. In another example, the activities outlined herein may be implemented with fixed logic or programmable logic (e.g., software/computer instructions executed by a processor) and the elements identified herein could be some type of a programmable processor, programmable digital logic (e.g., a field programmable gate array (FPGA), an EPROM, an EEPROM) or an ASIC that includes digital logic, software, code, electronic instructions, or any suitable combination thereof. Any of the potential processing elements, modules, and machines described herein should be construed as being encompassed within the broad term ‘processor.’
FIG. 3 is a simplified interaction diagram illustrating potential operations that may be associated with example embodiments of network environment 10 with a firewall cache that identifies a firewall for a managed route. FIG. 3 includes application 60, firewall agent 75, and firewall cache 77, which may be installed in a user host, such as user host 20a, for example. FIG. 3 also illustrates host manager 80, metadata cache 95, and policy module 85, which may be installed in a firewall such as firewall 25, for example. An intranet 78, Internet 15, and server 45 are also depicted in FIG. 3.
An application such as application 60 may attempt to open a new TCP connection at 305, with a server such as server 45, for example. Firewall agent 75 may intercept and hold the new connection, consulting firewall cache 77 (which may be initialized from configuration) at 310 to identify a firewall associated with the route to server 45. In the particular example of FIG. 3, a firewall associated with host manager 80 (e.g., firewall 25) may be identified and a connection (e.g., a DTLS connection) to the firewall may be opened at 315, using a certificate (e.g., client certificate 70) distributed by a policy server, for example. The connection may also be added to firewall cache 77 at 320 for future connections. Firewall agent 75 may send metadata for the connection to host manager 80 at 325a via a DTLS packet, for example. Host manager 80 may store the metadata in metadata cache 95 at 325b. Firewall agent 75 may release the connection at 330a, allowing data from application 60 to flow to host manager 80. Host manager 80 may provide connection data (i.e., TCP flow data, such as source IP address/port, destination IP address/port, protocol, etc.) to policy module 85 at 330b, and policy module 85 may correlate the connection data with metadata from metadata cache 95 at 335 to apply appropriate network policy at 340. In the example of FIG. 3, network policy permits the connection, so the connection may be released to server 45 at 345 and data may flow between server 45 and application 60 at 350.
FIG. 4 is a simplified interaction diagram illustrating potential operations that may be associated with example embodiments of network environment 10 with a stale firewall cache that identifies an invalid firewall for a managed route. FIG. 4 includes application 60, firewall agent 75, and firewall cache 77, which may be installed in a user host, such as user host 20a, for example. FIG. 4 also illustrates host manager 80, metadata cache 95, and policy module 85, which may be installed in a firewall such as firewall 25, for example. An intranet 78, Internet 15, server 45, and an invalid firewall 100 are also depicted in FIG. 4.
An application such as application 60 may attempt to open a new flow at 405, with a server such as server 45, for example. Firewall agent 75 may intercept and hold the new flow, and consult firewall cache 77 (which may be initialized from configuration) at 410 to identify a firewall associated with the route to server 45. In the particular example of FIG. 4, firewall cache 77 may include a stale entry that identifies firewall 100 for the route to server 45, such as might occur if a laptop or other mobile device moves from one network to another. Thus, firewall agent 75 may open, attempt to open, or believe it has previously opened a connection (e.g., a DTLS connection) to firewall 100 at 415, using a certificate distributed by a policy server, for example. The DTLS connection to firewall 100 may also be added to firewall cache 77 at 420 for future connections. Firewall agent 75 may fail to open a DTLS connection at 415, or it may send metadata for the connection to firewall 100 via a DTLS packet at 425 if it believes a connection is already open. Firewall 100 may never receive the metadata since it may no longer even be accessible to firewall agent 75 (e.g., there is no route to firewall 100), in which case the metadata is lost in transmission. If firewall 100 receives the metadata, it may be added to a metadata cache associated with firewall 100, but may be ignored since firewall 100 is no longer responsible for managing the route to server 45 in this particular example. Firewall agent 75 may release the new flow and data from application 60 may flow to host manager 80 at 430a. Host manager 80 may provide flow data to policy module 85 at 430b, and policy module 85 may attempt to correlate the flow data with metadata from metadata cache 95 at 435 to apply appropriate network policy at 440. However, since metadata for the flow was sent to another firewall (e.g., firewall 100) in this example scenario, policy module 85 may be unable to retrieve the metadata for the flow at 435. In the example of FIG. 4, though, network policy may permit the flow without metadata, so the flow may be released to server 45 at 445 and data may flow between server 45 and application 60 at 450.
Policy module 85 may log the event (i.e., releasing a new flow without metadata) and notify host manager 80 at 455a. Host manager 80 may send a discovery redirect to firewall agent 75 at 455b, which may include an HMAC based on a shared secret. Firewall agent 75 can receive the discovery redirect, and may also authenticate the discovery redirect based on the HMAC, for example, and update firewall cache 77 accordingly at 460. Firewall agent 75 may also open a connection (e.g., a DTLS connection) to host manager 80 and send metadata at 465. Host manager 80 may store in the metadata in metadata cache 95 at 470. The metadata can be audited along with the flow, which is already passing through the firewall associated with host manager 80.
FIG. 5 is a simplified interaction diagram illustrating potential operations that may be associated with other example embodiments of network environment 10 with a stale firewall cache that identifies an invalid firewall for a managed route. FIG. 5 includes application 60, firewall agent 75, and firewall cache 77, which may be installed in a user host, such as user host 20a, for example. FIG. 5 also illustrates host manager 80, metadata cache 95, and policy module 85, which may be installed in a firewall such as firewall 25, for example. An intranet 78, Internet 15, server 45, and invalid firewall 100 are also depicted in FIG. 5.
An application such as application 60 may attempt to open a new TCP connection at 505, with a server such as server 45, for example. Firewall agent 75 may intercept and hold the new connection, and consult firewall cache 77 at 510 to identify a firewall associated with the route to server 45. In the particular example of FIG. 5, firewall cache 77 may include a stale entry that identifies firewall 100 for the route to server 45, such as might occur if a laptop or other mobile device moves from one network to another. Firewall cache 77 may also identify an open connection 515 to firewall 100 in this scenario. Thus, firewall agent 75 may send metadata for the connection to firewall 100 via a DTLS packet at 520, but since firewall 100 is no longer responsible for managing the route to server 45 in this particular example, this metadata may be generally ignored by firewall 100. Firewall agent 75 may release the connection and data from application 60 may flow to host manager 80 at 525a. Host manager 80 may provide connection data to policy module 85 at 525b, and policy module 85 may attempt to correlate the connection data with metadata from metadata cache 95 at 530 to apply appropriate network policy at 535. However, since metadata for the connection was sent to another firewall (e.g., firewall 100) in this example scenario, policy module 85 may be unable to retrieve the metadata for the connection at 530. In the example of FIG. 5, network policy may block the connection without metadata at 535, so the firewall (e.g., host manager 80 or policy module 85) may drop the initial connection packet, without attempting to reset the connection (e.g., by sending a TCP RST packet).
Policy module 85 may log the event (i.e., dropping the initial connection packet because no metadata was received) and notify host manager 80 at 540a. Host manager 80 may send a discovery redirect to firewall agent 75 at 540b. Firewall agent 75 can receive the discovery redirect, and may also authenticate the discovery redirect based on an HMAC, for example, and update firewall cache 77 accordingly at 545. In the general case, application 60 retransmits its connection request at 550 if the firewall drops the initial connection packet (without resetting the connection) and application 60 does not receive an acknowledgement (e.g., an ACK packet) from server 45. Firewall agent 75 may again intercept and hold the connection, and consult firewall cache 77 at 555 to identify a firewall associated with the route to server 45. Updated firewall cache 77 may then identify a firewall associated with host manager 80 (e.g., firewall 25). Firewall agent 75 may also open a connection (e.g., a DTLS connection) to host manager 80 at 560 and add the new connection to firewall cache 77 at 565 for future connections. Firewall 75 may send metadata at 570a, which host manager 80 may store in metadata cache 95 at 570b. 
Firewall agent 75 may release the connection at 575a, allowing data from application 60 to flow to host manager 80. Host manager 80 may send connection data to policy module 85 at 575b, and policy module 85 may correlate the connection data with metadata from metadata cache 95 at 580 to apply appropriate network policy at 585. In the example of FIG. 5, network policy permits the connection, so the connection may be released to server 45 at 590 and data may flow between server 45 and application 60 at 595.
In another embodiment, host manager 80 may cache the initial connection packet for a brief period, enabling a connection to proceed when metadata is received at 570b without waiting for application 60 to retransmit the initial connection packet, which can make traffic flow faster. In yet another embodiment, firewall agent 75 can cache the initial connection packet and retransmit it when it receives a discovery redirect.
In various other scenarios, a firewall agent may have no information on a firewall (not even configuration information). In some embodiments, the firewall agent may allow a new flow through to a firewall without sending metadata. If the firewall receives the new flow without metadata, the flow may be processed substantially similarly to receiving a flow from a firewall agent having a stale firewall cache entry, such as described above with reference to FIG. 4 and FIG. 5. In such a scenario, the firewall agent incurs no overhead for flows over unmanaged routes.
A host agent may also send a PING message to a preconfigured address to force discovery for a particular path, such as by sending a PING message to a public Internet address to force discovery for the Internet path. A host agent may also send such a PING message on initial connection to a new network device.
As illustrated in various example embodiments above, a firewall cache may be updated in response to a discovery redirect, such as at 460 and 545. In more particular embodiments, a firewall agent may update its firewall cache by adding the subnet associated with the redirect message (e.g., a /24 entry for IPv4, /64 for IPv6). Alternatively, a firewall agent may search the firewall cache for the longest prefix matching the target address and add a new entry associating the firewall/port identified in the discovery redirect with the target address masked by eight bits (i.e., target/8=firewall:port) for IPv4 or by sixteen bits (i.e., target/16=firewall:port) for IPv6.
If a matching entry is found in the firewall cache, the firewall agent may compare the entry to the firewall/port identified in the discovery redirect. If the firewall/port from the discovery redirect does not match the firewall/port in the applicable firewall cache entry, the firewall cache may be updated by adding a new entry for the discovery target with a mask length incrementally modified (i.e., splitting the entry by incrementally increasing or decreasing the granularity of the entry for the discovery target) over the matching entry.
For example, the mask length of an entry may be increased by eight bits and the resulting network identifier associated with the discovery target. If the entry cannot be split further (i.e., the mask length is already 32 bits for an IPv4 address), the entry may be replaced such that the entry associates the discovery target with the firewall/port in the discovery redirect (i.e., replace the entry with target/32=redirect firewall:port).
In another example, a firewall cache entry may be split by adding a more specific entry (e.g., /24 for IPv4 or /64 for IPv6) and then generalized if overlapping discovery redirects are received. A firewall's routing knowledge may also be used to determine granularity or subnets associated with an exempt zone may be conveyed to a firewall agent in some embodiments.
Network environment 10 may also operate seamlessly with unmanaged routes. For example, a firewall agent may intercept a new connection from an application to a server and determine from a firewall cache that the route is unmanaged. The firewall agent may release the connection and the connection with the server may be established with no additional packet overhead.
FIG. 6 is an example packet data unit (PDU) format 600 that may be associated with exchanging metadata over a metadata channel in example embodiments of network environment 10. PDU format 600 may include, for example, network flow data 605 and session descriptor data 610. Network flow data 605 may provide information associated with a new flow from a source, such as an application on a managed host. In PDU format 600, for instance, network flow data 605 may identify a protocol (short protocol) (e.g., TCP, UDP, ICMP, GRE, IPSec, etc.), the IP address of the source node (IPaddress source_address), the port number of the process opening the connection (short source_port), the IP address of the destination node (IPaddress dest_address), and the port number of the process receiving the connection on the destination node (short dest_port). Session descriptor 610 may provide information about a user associated with the application opening the connection, such as a secure ID (string sid), a domain associated with the user (string domain), and a user name (string user), as well as information about the application, such as the full path of the application (string application_path). Other information in session descriptor 610 may provide data about the state of the source node (e.g., a host), including the state of a host firewall (boolean FW_enabled) and antivirus software running on the host (boolean AV_enabled), and information about interfaces on the source node (Interface interfaces[ ]). PDU format 600 is merely illustrative, though, and may be readily adapted to provide alternative or additional metadata, such as information about an intrusion prevention system, routing information, additional vendor information, etc.
Network environment 10 may provide significant advantages, some of which have already been discussed. For example, network environment 10 can provide security of host/firewall interlock data with low protocol overhead. Network environment 10 may be readily adapted to reuse standard code packages, leveraging configuration data, protocols such as DTLS, and timers in TCP and application layer protocols.
In the examples provided above, as well as numerous other potential examples, interaction may be described in terms of two, three, or four network elements. However, the number of network elements has been limited for purposes of clarity and example only. In certain cases, it may be easier to describe one or more of the functionalities of a given set of operations by only referencing a limited number of network elements. It should be appreciated that network environment 10 is readily scalable and can accommodate a large number of components, as well as more complicated/sophisticated arrangements and configurations. Accordingly, the examples provided should not limit the scope or inhibit the broad teachings of network environment 10 as potentially applied to a myriad of other architectures. Additionally, although described with reference to particular scenarios, where a particular module, such as policy module 85, is provided within a network element, these modules can be provided externally, or consolidated and/or combined in any suitable fashion. In certain instances, such modules may be provided in a single proprietary unit.
It is also important to note that the steps in the appended diagrams illustrate only some of the possible scenarios and patterns that may be executed by, or within, network environment 10. Some of these steps may be deleted or removed where appropriate, or these steps may be modified or changed considerably without departing from the scope of teachings provided herein. In addition, a number of these operations have been described as being executed concurrently with, or in parallel to, one or more additional operations. However, the timing of these operations may be altered considerably. The preceding operational flows have been offered for purposes of example and discussion. Substantial flexibility is provided by network environment 10 in that any suitable arrangements, chronologies, configurations, and timing mechanisms may be provided without departing from the teachings provided herein.
Numerous other changes, substitutions, variations, alterations, and modifications may be ascertained to one skilled in the art and it is intended that the present disclosure encompass all such changes, substitutions, variations, alterations, and modifications as falling within the scope of the appended claims. In order to assist the United States Patent and Trademark Office (USPTO) and, additionally, any readers of any patent issued on this application in interpreting the claims appended hereto, Applicant wishes to note that the Applicant: (a) does not intend any of the appended claims to invoke paragraph six (6) of 35 U.S.C. section 112 as it exists on the date of the filing hereof unless the words “means for” or “step for” are specifically used in the particular claims; and (b) does not intend, by any statement in the specification, to limit this disclosure in any way that is not otherwise reflected in the appended claims.

## Claims

1. A method for redirected firewall discovery, the method comprising:
transmitting a network flow from a source node to a first firewall;
transmitting, from the source node to a second firewall, metadata associated with the network flow;
receiving, from the first firewall at the source node, a discovery redirect including information identifying the first firewall; and
in response to receiving the discovery redirect, transmitting the metadata from the source node to the first firewall, the metadata associated with a network policy applicable to the network flow at the first firewall.

2. The method of claim 1, further comprising:
in response to receiving the discovery redirect, updating a firewall cache at the source node to include the first firewall as a firewall corresponding to a route associated with the network flow, the updating the firewall cache including adding a subnet associated with the discovery redirect to the firewall cache, or generalizing one or more existing entries in the firewall cache if the discovery redirect overlaps with previously received discovery redirects.

3. The method of claim 1, further comprising:
holding, using a firewall agent at the source node, a connection establishing packet of the network flow until the metadata is transmitted to the first firewall; and
transmitting the connection establishing packet to the first firewall.

4. The method of claim 1, further comprising:
in response to receiving the discovery redirect, authenticating the discovery redirect using a hash-based message authentication code (HMAC), the HMAC including a cryptographic hash function in combination with a secret shared between the first firewall and the source node.

5. The method of claim 1, further comprising:
in response to receiving the discovery redirect, retransmitting a connection establishing packet of the network flow to the first firewall, the connection establishing packet being cached at the source node.

6. A source node for redirected firewall discovery, the source node comprising:
an interface that transmits a network flow to a first firewall and transmits, to a second firewall, metadata associated with the network flow, wherein
the interface receives, from the first firewall, a discovery redirect including information identifying the first firewall, and
the interface is configured to transmit, in response to receiving the discovery redirect, the metadata to the first firewall, the metadata associated with a network policy applicable to the network flow at the first firewall.

7. The source node of claim 6, further comprising:
a processor that performs, in response to a reception of the discovery redirect, an update of a firewall cache at the source node to include the first firewall as a firewall corresponding to a route associated with the network flow, the update including adding a subnet associated with the discovery redirect to the firewall cache, or generalizing one or more existing entries in the firewall cache if the discovery redirect overlaps with previously received discovery redirects.

8. The source node of claim 6, further comprising:
a memory that holds a connection establishing packet of the network flow until the metadata is transmitted to the first firewall, wherein the interface transmits the connection establishing packet to the first firewall.

9. The source node of claim 6, further comprising:
a processor configured to authenticate, in response to a reception of the discovery redirect, the discovery redirect using a hash-based message authentication code (HMAC), the HMAC including a cryptographic hash function in combination with a secret shared between the first firewall and the source node.

10. The source node of claim 6, wherein the interface retransmits, in response to receiving the discovery redirect, a connection establishing packet of the network flow to the first firewall, the connection establishing packet being cached at the source node.

11. A method implemented by a firewall, the method comprising:
intercepting, at the firewall, a connection establishing packet of a network flow received over a network environment from a source node;
determining whether the firewall has metadata associated with the network flow in a metadata cache of the firewall;
in response to determining that the firewall does not have the metadata, transmitting, from the firewall to the source node, a discovery redirect including information to allow the source node to identify the firewall; and
receiving, at the firewall from the source node, the metadata, after the transmitting the discovery redirect to the source node.

12. The method of claim 11, further comprising:
in response to determining that the firewall does not have the metadata:
releasing the network flow without the metadata; and
logging an event that the network flow is released to indicate to a host manager at the firewall that the discovery redirect is to be sent to the source node.

13. The method of claim 11, further comprising:
in response to determining that the firewall does not have the metadata:
blocking the network flow without the metadata; and
logging an event that the network flow is blocked to indicate to a host manager at the firewall that the discovery redirect is to be sent to the source node.

14. The method of claim 13, wherein the blocking the network flow includes:
dropping the connection establishing packet without attempting to reset a connection associated with the network flow.

15. The method of claim 11, further comprising:
providing, from a host manager at the firewall to a policy module at the firewall, connection data associated with the network flow, the connection data including a source internet protocol address and port, a destination internet protocol address and port, and a protocol; and
correlating, using the policy module at the firewall, the connection data with metadata in the metadata cache to apply a network policy to the network flow.

16. An apparatus that implements a firewall, the apparatus comprising:
an interface that intercepts a connection establishing packet of a network flow received over a network environment from a source node; and
a processor that determines whether the firewall has metadata associated with the network flow in a metadata cache of the firewall, wherein
the interface transmits, in response to a determination that the firewall does not have the metadata, a discovery redirect to the source node, the discovery redirect including information to allow the source node to identify the firewall, and
the interface receives, from the source node, the metadata, after transmitting the discovery redirect to the source node.

17. The apparatus of claim 16, wherein the processor, in response to the determination that the firewall does not have the metadata, both releases the network flow without the metadata and logs an event that the network flow is released to indicate to a host manager that the discovery redirect is to be sent to the source node.

18. The apparatus of claim 16, wherein the network flow is blocked, in response to the determination that the firewall does not have the metadata, and
the processor logs an event that the network flow is blocked to indicate to a host manager at the firewall that the discovery redirect is to be sent to the source node, in response to the determination that the firewall does not have the metadata.

19. The apparatus of claim 18, wherein the network flow is blocked by a dropping of the connection establishing packet without an attempt to reset a connection associated with the network flow.

20. The apparatus of claim 16, wherein connection data associated with the network flow is provided from a host manager at the firewall to a policy module at the firewall, the connection data including a source internet protocol address and port, a destination internet protocol address and port, and a protocol, and
the processor correlates, using the policy module at the firewall, the connection data with metadata in the metadata cache to apply a network policy to the network flow.