Patent Publication Number: US-2022239561-A1

Title: Using physical location to modify behavior of a distributed virtual network element

Description:
CLAIM OF BENEFIT TO PRIOR APPLICATIONS 
     The present application claims the benefit of U.S. Provisional Patent Application 62/057,963, filed Sep. 30, 2014. U.S. Provisional Patent Applications 62/057,963 is incorporated herein by reference. 
    
    
     BACKGROUND 
     The benefits of network virtualization are well known. VMware® NSX® is a product suite that allows for virtualizing the network for VMs. NSX provides the network elements as fundamental building blocks of a distributed virtual network, elements such as Distributed Logical Switches (for providing L2 based packet forwarding) and Distributed Logical Routers (for providing L3 based packet forwarding). 
     The notion of a distributed logical network element (e.g., a distributed logical Switch or Router) is powerful since it allows the operator a construct a virtual network while hiding the underlying physical network connectivity and its limitations. The only thing required from the underlying physical infrastructure is that it is capable of forwarding Ethernet encapsulated IP frames. 
     The distributed logical network element is instantiated on a number of physical nodes (e.g. hypervisors) that participate in the logical network. These nodes also provide uniform packet forwarding capabilities in software. The control plane is responsible in configuring these uniform policies on the participating hypervisor nodes. These policies and configurations are necessarily at the logical level. In other words, they are not concerned with the underlying physical topology. This approach works well where the underlying physical network provides “uniform connectivity” to all participating hypervisors. By “uniform connectivity”, all the hypervisors are connected to a network with similar properties like latency, throughput, etc. 
     SUMMARY 
     Some embodiments of the invention provide a system for network virtualization in which physical network resources in different physical contexts are configured to implement one or more distributed logical network elements, at least some of the physical network resources implementing the distributed logical network elements being configured according the physical context of those network resources. In some embodiments, some of the distributed logical network elements are logical forwarding elements such as distributed logical switches and/or distributed logical routers. In some embodiments, the distributed logical network elements are implemented by virtualization software or hypervisors running on host machines that are situated in different physical locales (e.g., sites or data centers). 
     In some embodiment, a local configuration of a physical locale is a version of the logical configuration that is modified specifically for the physical locale. In some embodiments, such modification is based on locale identifiers that are assigned to the physical locales. In some embodiments, the local configuration is locally provided by the physical locale itself. In some embodiments, the local configuration is provided by a centralized network controller or manager, which delivers local configurations to each of the physical locales. In some embodiments, local configurations are embedded in the logical configuration of the entire network, and it is up to a physical locale to identify portions of the logical configuration as being applicable to that physical locale. The networking and computing resources of the locale (e.g., virtualization software in host machines) in turn uses the assigned locale identifier to identify applicable local configuration embedded in the logical configuration. 
     Different embodiments use locale-specific information differently to modify the behavior of distributed logical network elements. Some embodiments use locale-specific information to modify next-hop preference. Some embodiments perform ECMP to select the next hop from VMs, MPSEs, and/or MPREs based on locale-specific information. In some embodiments, locally modified configurations are used to determine the placement of VMs. In some embodiments, a VM placement engine uses locale specific information to decide the placement of VMs, i.e., to select a suitable host machine in a suitable physical locale hosting the VM based on the locale-specific information of all the physical locales. 
     The preceding Summary is intended to serve as a brief introduction to some embodiments of the invention. It is not meant to be an introduction or overview of all inventive subject matter disclosed in this document. The Detailed Description that follows and the Drawings that are referred to in the Detailed Description will further describe the embodiments described in the Summary as well as other embodiments. Accordingly, to understand all the embodiments described by this document, a full review of the Summary, Detailed Description and the Drawings is needed. Moreover, the claimed subject matters are not to be limited by the illustrative details in the Summary, Detailed Description and the Drawings, but rather are to be defined by the appended claims, because the claimed subject matters can be embodied in other specific forms without departing from the spirit of the subject matters. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The novel features of the invention are set forth in the appended claims. However, for purpose of explanation, several embodiments of the invention are set forth in the following figures. 
         FIG. 1  illustrates a network in which distributed logical network elements are implemented over physical elements that are each configured according the physical contexts of those physical elements. 
         FIG. 2  conceptually illustrates the available networking and computing resources in the physical locales of the network. 
         FIG. 3  illustrates the virtualization software running in host machines in the different locales. 
         FIG. 4  illustrates using assigned locale identifier to identify applicable portions of the logical configuration. 
         FIG. 5  conceptually illustrates the modification of logical configuration into locale-specific configuration at the physical locales. 
         FIGS. 6 a - b    conceptually illustrate processes for using physical location information to modify the behaviors of distributed logical network elements in logical configurations. 
         FIG. 7  conceptually illustrates using locale specific modification when performing ECMP for deciding the next hop of a distributed logical network elements. 
         FIG. 8  illustrates a VM placement engine that uses locale-specific information to decide the placement of VMs in a network. 
         FIG. 9  illustrates an example host machine that is operating virtualization software. 
         FIG. 10  conceptually illustrates an electronic system with which some embodiments of the invention are implemented. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, numerous details are set forth for the purpose of explanation. However, one of ordinary skill in the art will realize that the invention may be practiced without the use of these specific details. In other instances, well-known structures and devices are shown in block diagram form in order not to obscure the description of the invention with unnecessary detail. 
     Network virtualization is powerful because it frees the operator of the network from having to actively manage the underlying physical network connectivity and limitations. However, in many instances, being aware of its own physical context allows a hypervisor to optimize its own performance and throughput based on its physical context, even while participating in a logical network element for network virtualization. Such physical context includes the hardware of the host machine that implements hypervisor, and of the local networking environment within which the host machine is situated. For a host machine that is situated in a data center, the infrastructure of the site also constitutes the physical context of the hypervisor. 
     Some embodiments of the invention provide a system for network virtualization in which physical network resources in different physical contexts are configured to implement one or more distributed logical network elements, at least some of the physical network resources implementing the distributed logical network elements being configured according the physical context of those network resources. In some embodiments, some of the distributed logical network elements are logical forwarding elements such as distributed logical switches and/or distributed logical routers. In some embodiments, the distributed logical network elements are implemented by virtualization software or hypervisors running on host machines that are situated in different physical locales (e.g., sites or data centers).  FIG. 1  illustrates a network  100  in which distributed logical network elements are implemented over physical elements that are each configured according the physical contexts of those physical elements. 
       FIG. 1  includes a logical view  101  and a physical view  102  of the network  100 . The logical view of the network  100  is a logical abstraction of the system that hides or encapsulates underlying physical realities of the network. Managing the network  100  through its logical abstraction frees the operator of the network from having to manage the actual physical peculiarities of the network. In some embodiments, the logical view  101  reflects a view of the network  100  as defined according to a logical configuration  105 . The underlying physical infrastructure is in turn configured according to the logical configuration in order to implement the network  100 . 
     As illustrated, the logical view  101  (or the logical configuration) of the network includes virtual machines (VM)  111 - 118 , a logical switch (L2 forwarding elements)  121  for a network segment A, a logical switch  122  for network segment B, a logical router/bridge (L3 forwarding element)  131 , and an edge gateway  141 . The VMs  111 - 114  belong to the network segment A and are interconnected by the logical switch  121 . The VMs  115 - 118  belong to the network segment B and are interconnected by the logical switch  122 . The network segments A and B ( 121  and  122 ) are interconnected by the logical router/bridge  131 , which is in turn connected to the Internet through the edge gateway  141 . In some embodiments, a network segment can be an IP subnet (such as VLAN) or an encapsulation overlay network such as VXLAN. In some embodiments, each L2 network segment is identified by or referred to by a network segment identifier such as VNI (VXLAN network identifier). The logical router/bridge  131  forwards packet between different network segments  121  and  122 . In some embodiments, the logical router/bridge  131  forward packets by L3 routing (e.g., using destination L3 IP address to look up destination VNI and destination L2 MAC address) and/or by bridging (using destination L2 MAC address to lookup destination VNI). 
     In some embodiments, the logical configuration is specified irrespective of the underlying physical realities. In other words, the logical configuration is produced as if the connectivity of the underlying physical infrastructure is uniform and there is no distinction between resources in one locale versus resources in another locale. However, in some embodiments, the logical configuration is implemented over network resources that are situated in different physical locations such that each distributed logical network element (such as  121 ,  122 , and  131 ) can span across multiple physical locations. 
     The physical view  102  illustrates the underlying physical infrastructure that implements the logical configuration of the network  100 . As illustrated, the network  100  is implemented over four physical locales  191 - 194  (“SFO”, “LAX”, “SJC”, and “NYC”). The four physical locales  191 - 194  are interconnected by inter-locale connections  180 , which is provided by the Internet in some embodiments. Each of these locales provides a set of computing resources for implementing virtual machine as sell as networking resources for implementing logical switches and routers/bridges. 
     The logical switches  121  and  122 , as well as the logical router/bridge  131  of the logical configuration  105  span the four physical locales. Each of these logical forwarding elements ( 121 ,  122 , and  131 ) are implemented in a distributed fashion by the physical forwarding elements in those four locales  191 - 194 . Specifically, the logical switch  121  is implemented by physical forwarding elements A1-A2 of locale  191 , A3-A4 of locale  192 , A5-A6 of locale  193 , and A7-A8 of locale  194 . The logical switch  122  is implemented by physical forwarding elements B1-B2 of locale  191 , B3-B4 of locale  192 , B5-B6 of locale  193 , and B7-B8 of locale  194 . The logical router/bridge  131  is implemented by physical forwarding elements R1-R2 of locale  191 , R3-R4 of locale  192 , R5-R6 of locale  193 , and R7-R8 of locale  194 . In other words, the forwarding elements are implemented on networking and/or computing resources that span the four physical locales  191 - 194 . 
     The VMs  111 - 118  (V1-V8) are likewise implemented on computing resources that span the four physical locales. Specifically, the VMs  111 - 112  are implemented by computing resources in “SFO”, the VMs  113 - 114  are implemented by computing resources in “LAX”, the VMs  115 - 116  are implemented by computing resources in the locale “SJC” ( 193 ), and the VMs  117 - 118  are implemented by computing resources in the locale “NYC” ( 194 ). 
     In some embodiments, each physical locale is a data center that includes its own collection of interconnected network resources. Each physical location has its own set of properties, capabilities and limitations. Such local properties can include the number and types of networking and computing resources available, the bandwidth of interconnections connecting the networking resources, the latencies for sending data packets between the networking and computing resources, etc. The different physical locales can also be geographically separated as to impose significant latency for data to travel from one physical locale to another. The communication mediums that links the different physical locations are likely of limited speed and throughput (e.g., the Internet) when compared with what is available within a data center or within a computing device. 
     Each physical locale is associated with a set of local configurations that is based on the properties, capabilities, and limitations of the physical locale. When applied, the local configuration of a physical locale modifies the behavior of networking and computing resources of the physical locale away from the uniformity specified by the logical configuration in some embodiments. In some embodiments, the local configuration of a physical locale is based on locale specific properties of the physical locale. This is unlike a logical configuration in some embodiments, which hides the local peculiarities of the different locales from user and treats the entire network as a uniform pool of resources and connections. In some embodiments, the local configuration of a locale distinguishes physical components in the locale from physical components from other locales. In some embodiments, the local configuration prefers or forbids using certain network resources under certain conditions. In some embodiments, the local configuration reserves network resources for traffic from certain nodes. In some embodiments, the local configuration is based on performance metrics (such as latency, available memory, available bandwidth, etc.) of physical components in the network. In some embodiments, the local configuration is made to optimize resource usage in the physical locale in order to balance load, avoid congested routing resources, guarantee bandwidth, or perform equal cost multi-path routing (ECMP). 
     As illustrated, the local configurations of the locales  191 - 194  (“SFO”, “LAX”, “SJC”, and “NYC”) are conceptually illustrated as having local configurations  151 ,  152 ,  153 , and  154 , respectively. These local configurations are unlike the logical configuration (i.e., the logical view  101 ) of the network, which is applicable uniformly to all four physical locales. The local configuration  151  is applicable only to resources within the locale “SFO”. The local configuration  152  is applicable only to resources within the locale “LAX”. The local configuration  153  is applicable only to resources within the locale “SJC”. The local configuration  154  is applicable only to resources within the locale “NYC”. 
       FIG. 2  conceptually illustrates the available networking and computing resources in the physical locales  191 - 194  (“SFO”, “LAX”, “SJC”, “NYC”) of the network  100 . As illustrated, each physical locale includes a set of computing devices labeled as “host” (hosts  211 - 213  in the locale  191 , hosts  221 - 223  in the locale  192 , hosts  231 - 233  in the locale  193 , and hosts  241 - 243  in the locale  194 ). These computing devices are running virtualization software (labeled “VSW”) that allows the computing resource to serve as host machines of VMs. The virtualization software running in the host machines are configured according to the logical configuration  105  of the network  100 , which allows the host machines to instantiate local copies of the logical switch  121 - 122  and of the logical router/bridge  131  as physical forwarding elements. Some of the physical locales also include networking devices labeled as “ToR” (Top of Rack) or “PH” (physical routers). These network devices perform packet forwarding tasks (L3/L2/bridging), but do not operate virtualization software. The host machines, ToRs, and PHs of a physical locale are interconnected by intra-locale connectivity of the physical locale. The computing and routing resources of the physical locale are then connected to the Internet through a gateway device labeled as “GWY”. 
     As mentioned, the computing and network resources of each physical locale are configured according to a set of local configuration in addition to the logical configuration of the network  100 . As illustrated, the computing and network resources (host machines, PH&#39;s, ToRs, etc) of the physical locales  191 - 194  are configured by local configurations  151 - 154 , respectively. In some embodiments, the local configurations are used to configure the computing and networking resource of each physical locale according to the local properties of each locale. For example, different locales can have different number of computing devices that serve as host machines. Different locale can have different types of computing devices that serve as host machines. Different locale can have different number or types of ToRs or PHs. The intra-locale connectivity of one locale can have different capacity or latency than the intra-locale connectivity of another locale. And sending packets to a computing or networking resource of a same locale through intra-locale connectivity generally requires less latency than through the Internet to a computing or networking resource of a different locale. 
       FIG. 3  illustrates the virtualization software running in host machines in the different locales. The virtualization software manages the operations of the VMs as well as their access to the computing resources and the network resources of the host machines. In some embodiments, the virtualization software provides an interface between each VM and a logical switch supported by the underlying network. Virtualization software may include one or more software components and/or layers, possibly including one or more of the software components known in the field of virtual machine technology as virtual machine monitors (VMMs), hypervisors, or virtualization kernels. Because virtualization terminology has evolved over time and has not yet become fully standardized, these terms do not always provide clear distinctions between the software layers and components to which they refer. As used herein, the term, “hypervisor” is intended to generically refer to a software layer or component logically interposed between a virtual machine and the host platform. Computing devices that serve as host machines will be further described in Section III below. 
       FIG. 3  illustrates four host machines  211 ,  221 ,  231 , and  241  that are in locales  191 - 194  (“SFO”, “LAX”, “SJC”, and “NYC”), respectively. Each of these host machines is running virtualization software that allows it to be part of the logical configuration  105  of the network  100 . The virtualization software allows its host machine to operate local instantiations of the logical switches and logical routers/bridges in the logical configuration. As mentioned, the logical configuration  105  includes the logical switches  121 - 122  and the logical router/bridge  131 . A local instantiation of the logical switch  121  in a host machine is a L2 physical switching element for the network segment A. A local instantiation of the logical switch  122  in a host machine is a L2 physical switching element for the network segment B. A local instantiation of the logical routing/bridging element in a host machine is a physical routing or bridging element. As these physical forwarding elements are managed by the virtualization software, they are also referred to as managed physical switching elements (MPSE) and managed physical routing elements (MPRE). Further descriptions of MPSEs, MPREs, logical routing elements (LREs), and logical switching elements (LSEs) can be found in U.S. patent application Ser. No. 14/137,862 filed on Dec. 20, 2013, titled “Logical Router”. U.S. patent application Ser. No. 14/137,862 is herein incorporated by reference. 
     According to the logical configuration  105  of the network  100 , the host machine  211  instantiates MPSEs  311  and  321  as physical forwarding elements A1, B1. The host machine  211  also instantiates an MPRE  331  as the physical forwarding element R1. The physical forwarding elements A3, B3, R3, A5, B5, R5, A7, B7, R7 are likewise implemented by instantiations of MPSEs and MPRE in the host machines  221 ,  231 , and  241 . (In some embodiments, MPSEs of different network segments in a same host machine are implemented as one MPSE in that host machine. Such an MPSE distinguishes L2 traffic of different network segment by VNI identifiers in some embodiments). 
     In addition to the MPSEs and the MPREs, the virtualization software of a host machine also implements local configurations that are specific to the physical locale or to the host machine. In some embodiments, the virtualization software of a host machine of a locale uses information specific to that locale to modify next hop decisions. As illustrated, the host machine  211  has information  341  specific to the locale “SFO”, and it uses this locale information to create or modify a set of next hop tables  351 . The MPSE  311  and the MPRE  321  in the host machines  211  in turn use the modified next hop tables to select the destination for the packets it produces. Likewise, the MPSEs and the MPREs in the host machines  221 ,  231 , and  241  also uses their respective local configuration or locale information to determine next hop. In other words, the physical locale information (or local configuration) modifies the behaviors of the distributed logical network elements (MPSEs and MPREs) that are specified by the logical configuration. 
     Several more detailed embodiments of the invention are described below. Section I describes methods for implementing locale-specific configuration for modifying the behavior of distributed logical network elements. Section II describes examples of using locale-specific configurations to modify behaviors of distributed logical network elements. Section III describes an example communications device that implements some embodiments of the invention. Finally, section IV describes an electronic system with which some embodiments of the invention are implemented. 
     I. Implementing Locale-Specific Configurations 
     Different embodiments implement local configurations specific to physical locales (or locale-specific configurations) differently. In some embodiment, a local configuration of a physical locale is a version of the logical configuration modified specifically for the physical locale. In some embodiments, such modification is based on locale identifiers that are assigned to the physical locales. In some embodiments, the local configuration is locally provided by the physical locale itself. In some embodiments, the local configuration is provided by a centralized network controller or manager, which delivers local configurations to each of the physical locales. In some embodiments, local configurations are embedded in the logical configuration of the entire network, and it is up to a physical locale to identify portions of the logical configuration as being applicable to that physical locale. The networking and computing resources of the locale (e.g., virtualization software in host machines) in turn uses the assigned locale identifier to identify applicable local configuration embedded in the logical configuration. 
     An example portion of a logical configuration is a definition of a route entry for a logical router (e.g., the logical router  131 ), which in some embodiments is a directive/command/definition/statement that looks like: 
       &lt;destination-network/prefix&gt; via nexthop &lt;nh&gt; forward on interface &lt;id&gt;  (1)
 
     Thus, a logical configuration statement “0/0 via nexthop 192.168.1.1 forward on interface lif0” would be globally applicable to all physical locales. However, this definition does not account for any modifier based on physical locales. A route entry having a locale based modifier looks like: 
       &lt;destination-network/prefix&gt; via nexthop &lt;nh&gt; on locale &lt;locale-id&gt; forward on interface &lt;id&gt;  (2)
 
     Such a route entry is a directive that allows locale-specific property to be taken into consideration. Thus, a route entry “0/0 via nexthop 192.168.1.1 on locale ‘NYC’ forward on interface lif0” is a route entry having locale modifier “NYC”. It is a local configuration that would be recognized as a local configuration specific to locale “NYC” while being ignored by other locales based on the locale ID “NYC”. Likewise a route entry “0/0 via nexthop 192.168.1.2 on locale ‘LAX’ forward on interface lif0” is a route entry having local modifier “LAX”. It would be recognized as a local configuration specific to locale “LAX” while being ignored by other locales based on the locale ID “LAX”. 
       FIG. 4  illustrates using assigned locale identifier to identify applicable portions of the logical configuration. The figure illustrates the logical configuration  105  for the network  100  that includes portions applicable to all physical locales as well as portions that are locale specific. As illustrated, the logical configuration  105  includes a globally applicable portion  410  that is applicable to all locales. The logical configuration  105  also includes portions  411 - 414  that are specific to locales  191 - 194  (“SFO”, “LAX”, “SJC”, and “NYC”), respectively. In some embodiments, such locale-specific portions of the logical configuration include directives having locale specific modifiers such as route entry (2) described above. 
     In order for each physical location to identify portions of the logical configuration  105  that are applicable to them, a network manager  150  first assigns locale identifiers to the physical locales. In some embodiment, each physical locale receives its locale identifier during an initial configuration phase of the network  100 . The physical locale then uses the receive locale ID to identify and apply applicable portions of the logical configuration while ignoring portions of the logical configuration that is applicable only to other physical locales. In other words, each physical locale uses the physical locale identifier as a filter to accept and apply only relevant portions of the logical configuration. For example, the locale “SFO” ( 191 ) uses its assigned locale identifier to accept only the global configuration  410  and the portion  411  that is specific to the locale “SFO”. In some embodiments, portions of the logical configuration that are specific to a physical locale are marked by the identifier of that physical locale, so each physical locale identifies the relevant portion of the logical configuration by comparing its own received physical locale ID with the locale IDs that marks the different portions of the logical configuration. A process for identifying locale-specific portions of logical configuration as local configuration is described by reference to  FIG. 6 a    below. 
       FIG. 4  also conceptually illustrates a filter for each of the physical locales (locale filters  421 - 424  for locales  191 - 194 , respectively), which uses the locale ID of its physical locale to filter-in relevant portions of the logical configuration for its locale. In some embodiments, the filtering of the logical configuration for a physical locale is performed by the networking and computing resources within the locale (such as by virtualization software of the host machines). In some embodiments, the filtering of the logical configuration is performed by a local configuration manager in each of the locales. 
     As mentioned, in some embodiment, a local configuration of a physical locale is a version of the logical configuration that is modified specifically for the physical locale. In some of these embodiments, at least some of the modification is performed at the physical locales themselves based on their locale-specific properties.  FIG. 5  conceptually illustrates the modification of logical configuration into locale-specific configuration at the physical locales. As illustrated, the network manager  150  delivers the logical configuration  105  to each of the physical locales  191 - 194 . Each of the physical locales then performs local modification on the received logical configuration based on information or properties specific to that locale to produce a set of local configuration specific to that locale. For example, the locale “SFO” ( 191 ) modifies logical configuration  105  into a SFO specific local configuration  511  based on SFO specific information  521 . The modification is performed by a local modification module  501 , which in some embodiments is part of the virtualization software operating in host machines of the physical locale  191 . 
     The locale specific information (e.g., the “SFO” local information  521 ) in some embodiments includes portions of the logical configuration that is relevant to the locale provided by the network manager  150 , such as the locale specific portions  411 - 414  of the logical configuration or the locale specific route entry for a logical router as described above. The locale specific information in some embodiments includes static network topology of the physical locale (e.g., a data center), which is provided by a central network manager in some embodiments in which the network manager has such information. In some embodiments, the locale specific information is furnished locally by a local network manager (e.g., the local manager  531  of the physical locale “SFO”  191 ). In some embodiments, the locally furnished information includes static network topology of the physical locale. In some embodiments, the locally furnished information includes dynamic network metrics of the physical locale that are updated in real time (such as latency, available memory, available bandwidth, etc.) A process for modifying logical configuration based on locale-specific information is described by reference to  FIG. 6 b    below. 
     For some embodiments,  FIGS. 6 a - b    conceptually illustrate processes for using physical location information to modify the behaviors of distributed logical network elements in logical configurations.  FIG. 6 a    conceptually illustrates a process  601  for using physical locale identifier to identify locale-specific portions of the logical configuration (or configuration definitions having a specific locale modifier).  FIG. 6 b    conceptually illustrates a process  602  for modifying logical configuration based on locale specific information. In some embodiments, the processes  601  and  602  are performed by the virtualization software of a host machine in a physical locale. 
     Some embodiments perform the process  601  during initial configuration of a network according to a logical configuration. For example, the host machines (i.e., their virtualization software) in the physical locales  191 - 194  perform the process  601  when the network manager  150  is configuring the underlying physical hardware according to the logical configuration  105 . 
     The process  601  starts when it receives (at  610 ) a locale identifier from the network manager. The locale identifier is the identifier that the network manager assigns to the physical locale that includes host machine running the process. The process then receives (at  620 ) logical configuration from the network manager. In some embodiments, the process receives the locale identifier and the logical configuration through control plane communications with the network manager. 
     Next, the process identifies (at  630 ) applicable portions of the logical configuration based on the received locale ID that is assigned to the physical locale of the host machine. In some embodiments, the process filters the logical configuration to accept only relevant portions of the logical configuration, i.e., the portions that are either globally applicable to all physical locations or the portions that are marked by the matching locale ID. In some embodiments, the relevant portions of the logical configuration are configuration definitions/statements/directives that are modified by a locale ID (e.g., the locale-ID-modified route entry (2)). 
     Finally, the process configures (at  640 ) the distributed logical network elements (e.g., MPSE and MPRE) by applying the portions of the logical configuration identified as relevant to this physical locale. In some embodiments, the globally applicable portions of the logical configuration instantiates the distributed logical network elements, while the locale-specific portions of the logical configuration modifies the behavior of the instantiated distributed logical network elements. The process  601  then ends. 
     The process  601  is a process for configuring a physical locale based on information provided by a network manager during an initial configuration of the network. The process  602  is on the other hand a process for modifying a received logical configuration. Some embodiments performs the process  602  after the initial configuration by modifying the received logical configuration based on locale specific information, which in some embodiments includes network topology from the perspective of the physical locale and/or static/dynamic network performance metrics that are provided by the physical locale. Some embodiments perform the process  602  during or soon after the initial configuration. 
     The process  602  receives (at  650 ) the logical configuration from network manager during initial configuration. The process  602  then identifies (at  660 ) the locale specific information. In some embodiments, the process  602  identifies the locale specific information within the configuration data transmitted by the central network manager. In some embodiments, the process  602  identifies the locale specific information from information that are available locally at the physical locale, such as dynamic real-time performance matric of the locale or the network topology of the locale. 
     The process then modifies (at  670 ) the logical configuration based on the identified locale specific information. The process then configures (at  680 ) the distributed logical network elements in the logical configuration by applying the modified logical configuration. For example, in some embodiments, the process modifies the logical configuration by modifying next hop preferences of a MPSE or MPRE based on identified locale information (hence modifying the MPSE/MPRE&#39;s behavior). The locale-specific information in some embodiments includes information on networking resources in the locale that allows a distributed logical network element to select or avoid a particular node as next hop. After applying the modified logical configuration, the process  602  ends. 
     II. Use Cases of Locale-Specific Configurations 
     Different embodiments use locale-specific information differently to modify the behavior of distributed logical network elements. For example, as mentioned, some embodiments use locale-specific information to modify next-hop preferences. Specifically, some embodiments perform ECMP to select the next hop from VMs, MPSE, and/or MPREs. The locale-specific information or modified logical configuration allows the next-hop selection for these globally configured distributed logical network elements to operate based on local information that are hidden from the central operator of the network. 
     For some embodiments,  FIG. 7  conceptually illustrates using locale specific modification when performing ECMP for deciding the next hop of a distributed logical network elements. The figure illustrates the modification of the logical configuration for the VM  112  (V2) and the MPSE  311  (A1) based on locale-specific information of the locale  191  “SFO” (since both V2 and A1 are instantiated in host machines of the locale  191 ). 
     As illustrated, the logical configuration  105  of the network  100  includes, among others, next hop table  701  for the VM  112  (V2) and next hop table  702  for the MPSE  311  (A1). The VM  112  belongs to network segment B, and hence all MPSEs of the logical switch B  122  (B1-B8) are eligible as next hop for the VM  112 . The MPSE  311  (A1) is an instantiation of the logical switch element  121  for the network segment A (logical switch A). Since the logical router  131  is a next hop of the logical switch A, all of the MPREs belonging to the logical router  131  (R1-R8) are eligible as next hop for MPSE  311 . However, these eligible hops are determined strictly from the logical configuration point of view without considering any locale-specific information. 
     The content of the logical configuration  111  is processed by the locale specific modification module  501  of the locale “SFO”. The module  501  uses information specific to the locale “SFO” (local information  521 ) to modify the logical configuration  105  for the distributed logical network elements (MPSEs and MPREs) running in the host machines of the physical locale “SFO”. In some embodiments (not illustrated), the locale specific modification is based on relevant portions of the logical configuration that are identified by a locale ID assigned by the network manager. The locale specific modification  501  produces a locale-modified configuration  711  for the VM  112  (V2) and a locale-modified configuration  712  for the MPSE  311  (A1) 
     The locale-modified configurations distinguish between the possible different next hops of a distributed logical network element. Specifically, the modified configuration  711  distinguishes between possible next hops B1-B8 based on their separation from the VM  112  (V2), while the modified configuration  712  distinguishes between the possible next hops R1-R8 based on their separation from the MPSE 311  (A1). Such distinctions are made possible by the locale specific information  521 , which identifies next hops in this physical locale/data center versus next hops in other physical locales/data center. For example, the modified configuration  711  identifies B1 and B2 as next hops in the same data center as V2 (also in locale “SFO”), B5 and B6 as next hops in a near data center (in locale “SJC”), B3, B4, B7, and B8 as next hops that are either far or very far (local “LAX” or “NYC”). Based on the information, a ECMP module  721  for the VM  112  will be able to next hop selection decisions that are optimized based on the locale specific information (e.g., by favoring or weighing toward next hops that are near or in the same data center). The ECMP module  722  likewise makes next hop decisions based on locale information that distinguishes between R1-R8 as next hops (R1 and R2 being in the same data center as A1, R5 and R6 being in a near data center, R3, R4, R7, R8 being in far data center). 
     The modified configuration  712  is an example local configuration that uses locale-specific parameters (i.e., geographic separation from the current locale) to characterize the possible next hops.  FIG. 7  also illustrates other example modified configurations ( 762  and  772 ) that use other locale-specific parameters to characterize the possible next hops. 
     The modified configuration  762  reports the latencies to/from the possible next hops R1-R8 of the MPSE 311  (A1). The ECMP module  722  can then use the reported latencies to select the next hop. As illustrated, next hops R1 and R2 has the smallest latencies (possibly because they are in the same locale “SFO”), while next hops R7 and R8 has the largest latencies (possibly because they are in a distant locale “NYC”). In some embodiments, the latency metrics reported in the modified configuration  762  are based on real-time measurements obtained by the physical hardware of the locale. In some embodiments, the latency metrics reported are historical averages that can be supplied locally by data center or centrally by the central network manager (e.g.,  150 ). 
     The modified configuration  772  specifies directives or commands that are associated with each of the possible next hops. As illustrated, R3, R4, R7, and R8 are specified as “forbidden” for traffic from MPSE A1, while R2 is specified as “preferred”. R1 has a directive that says “reserved for V1” such that only traffic originated from the VM  111  (V1) may use R1 as next hop. Directives such as these are used by some embodiments to guarantee bandwidth for a particular VM by e.g., reserving a networking resource for traffic from the particular VM. Such directives can be specified locally by the data center or centrally by the network manager (e.g.,  150 ) in some embodiments. 
     In some embodiments, modified configurations of different types are used jointly by ECMP modules when selecting a next hop. For example, the ECMP module  722  can use the information from any or all of the modified configurations  712 ,  762 , and  772  when selecting a next hop. Though not illustrated, other locale-specific parameters can also be used to characterize next hops (e.g., storage capacity of computing device, processor speed, etc.). More generally, different locale-specific parameters can be used to modify the behaviors of distributed logical network elements or to modify uniform/global logical configurations that are centrally specified by a network manager. 
     In some embodiments, locally modified configurations are used to determine the placement of VMs. As mentioned, a logical network may span multiple data centers in different geographical locations. In some embodiments, the operator or the user of the logical network does not specify or care which host machine in which data center is hosting the VM, but a VM placement engine uses locale specific information to decide the placement of VMs, (i.e., to select a suitable host machine in a suitable physical locale hosting the VM based on the locale-specific information of all the physical locales). 
     For some embodiments,  FIG. 8  illustrates a VM placement engine  810  that uses locale-specific information to decide the placement of VMs in a network. The figure illustrates the locale-specific information based VM placement in two stages  801 - 802 . 
     At the first stage  801 , the VM placement engine  810  receives locale-specific information  521 - 524  for the locales  191 - 194  (“SFO”, “LAX, “SJC”, and “NYC”). In some embodiments, such information are generated and provided by the physical locales (data centers) themselves. In some embodiments such information are maintained and provided centrally by the network manager (e.g.,  150 ). The VM placement engine  810  also receives a list of VMs that needs to be placed from the logical configuration  105  of the network  100 . 
     At the second stage  802 , the VM placement engine  810  assigns the VMs specified by the logical configuration to host machines in the different physical locales. The VM placement engine examines the locale specific information when selecting a locale and a host machine for a VM. In some embodiments, some or all of the VMs in the logical configuration are each associated with a unique set of requirements, and the placement engine in turn finds the most suitable host machine and physical locale for those VMs based on the VM&#39;s requirements and the locale&#39;s specific properties. For example, a particular VM may require certain bandwidth guarantee, and the VM placement engine would in turn use the locale-specific information to identify a physical locale and a host machine that can provide the requisite bandwidth. Such locale-specific information may in some embodiments include an identification of a particular distributed logical network element (MPSE or MPRE) running on a particular host machine that has sufficient bandwidth to handle the guaranteed bandwidth requirement. 
     Though not illustrated, in some embodiments, the VM placement engine sends directives to each of the locales after the placements of the VMs are decided. In some embodiments, such directives are also locale-specific, such as to reserve a particular networking or computing resource in the locale for a particular VM, or to require a particular next hop for a particular distributed logical network element, etc. In some embodiments, the delivery of such directives or command relies on locale IDs that were assigned to the locales by the network manager as described by reference to  FIG. 4  above. 
     III. Computing Device 
     As mentioned earlier, some embodiments of the invention are implemented by virtualization software or hypervisors running on computing devices serving as host machines. For some embodiments,  FIG. 9  illustrates an example host machine  900  that is operating virtualization software  905 . The virtualization software  905  allows the host machine to host virtual machines  911 - 914  as well as connecting the virtual machines to a physical network  990 . This physical network  990  may span one or more data centers and include various physical switches and routers. 
     As illustrated, the host machine  900  has access to the physical network  990  through a physical NIC (PNIC)  995 . The virtualization software  905  serves as the interface between the hosted VMs  911 - 914  and the physical NIC  995  (as well as other physical resources, such as processors and memory). Each of the VMs includes a virtual NIC (VNIC) for accessing the network through the virtualization software  905 . Each VNIC in a VM is responsible for exchanging packets between the VM and the virtualization software  905 . In some embodiments, the VNICs are software abstractions of physical NICs implemented by virtual NIC emulators. 
     The virtualization software  905  manages the operations of the VMs  911 - 914 , and includes several components for managing the access of the VMs to the physical network (by implementing the logical networks to which the VMs connect, in some embodiments). As illustrated, the virtualization software  905  includes a physical switching element  920 , a physical routing element  930 , a controller interface  940 , an uplink module  970 , and a locale-specific configuration module  950 . 
     The controller interface  940  receives control plane messages from a controller or a cluster of controllers  960 . In some embodiments, these control plane message includes configuration data for configuring the various components of the virtualization software and/or the virtual machines (such as the physical switching element  920  and the physical routing element  930 ). In some embodiments, the control plane messages also include locale-specific configuration information from a central network manager or a local network manager. 
     The physical switching element  920  (or managed physical switching element, MPSE) delivers network data to and from the physical NIC  995 , which interfaces the physical network  990 . The physical switching element also includes a number of virtual ports (vPorts) that communicatively interconnects the physical NIC with the VMs  911 - 914 , the physical routing element  930  and the controller interface  940 . Each virtual port is associated with a unique L2 MAC address, in some embodiments. The physical switching element performs L2 link layer packet forwarding between any two network elements that are connected to its virtual ports. The physical switching element also performs L2 link layer packet forwarding between any network element connected to any one of its virtual ports and a reachable L2 network element on the physical network  990  (e.g., another VM running on another host). 
     The physical routing element  930  (or managed physical routing element, MPRE) performs L3 routing (e.g., by performing L3 IP address to L2 MAC address resolution) on data packets received from a virtual port on the physical switching element  920 . In some embodiments, the virtual port that the physical routing element  930  is attached to is a sink port. Each routed data packet is then sent back to the physical switching element  920  to be forwarded to its destination according to the resolved L2 MAC address. This destination can be another VM connected to a virtual port on the physical switching element  920 , or a reachable L2 network element on the physical network  990  (e.g., another VM running on another host, a physical non-virtualized machine, etc.). 
     The locale specific configuration module  950  stores information specific to the physical locale of the host machine. The information is made available to the physical switching element  920  and the physical routing and bridging element  930 , which uses the locale specific information to modify their behavior by e.g., favoring or disfavoring specific next hops. In some embodiments, the locale specific configuration module uses a locale identifier to determine if data received from controller interface  940  is a locale-specific configuration data that is applicable to this host machine. The locale specific configuration module  950  in some of these embodiments act as a filter and allow only relevant configuration data to be used to modify the behavior of the physical switching element  920  and the physical routing element  930 . 
     The uplink module  970  relays data between the physical switching element  920  and the physical NIC  995 . In some embodiments, the uplink module  970  allows the host machine  900  to serve as a tunnel endpoint for encapsulation overlay networks such as VXLAN and VLANs. VXLAN is an overlay network encapsulation protocol. An overlay network created by VXLAN encapsulation is sometimes referred to as a VXLAN network, or simply VXLAN. When a VM on the host  900  sends a data packet (e.g., an ethernet frame) to another VM in the same VXLAN network but on a different host, the uplink module  970  encapsulates the data packet using the VXLAN network&#39;s VNI and network addresses of the VTEP, before sending the packet to the physical network. The packet is tunneled through the physical network (i.e., the encapsulation renders the underlying packet transparent to the intervening network elements) to the destination host. The uplink module  970  also decapsulates incoming VXLAN packets and forwards only the original inner data packet to the destination VM. 
     In this document, the term “packet” refers to a collection of bits in a particular format sent across a network. One of ordinary skill in the art will recognize that the term packet may be used herein to refer to various formatted collections of bits that may be sent across a network, such as Ethernet frames, TCP segments, UDP datagrams, IP packets, etc. 
     This specification refers throughout to computational and network environments that include virtual machines (VMs). However, virtual machines are merely one example of data compute nodes (DCNs) or data compute end nodes, also referred to as addressable nodes. DCNs may include non-virtualized physical hosts, virtual machines, containers that run on top of a host operating system without the need for a hypervisor or separate operating system, and hypervisor kernel network interface modules. 
     VMs, in some embodiments, operate with their own guest operating systems on a host using resources of the host virtualized by virtualization software (e.g., a hypervisor, virtual machine monitor, etc.). The tenant (i.e., the owner of the VM) can choose which applications to operate on top of the guest operating system. Some containers, on the other hand, are constructs that run on top of a host operating system without the need for a hypervisor or separate guest operating system. In some embodiments, the host operating system uses name spaces to isolate the containers from each other and therefore provides operating-system level segregation of the different groups of applications that operate within different containers. This segregation is akin to the VM segregation that is offered in hypervisor-virtualized environments that virtualize system hardware, and thus can be viewed as a form of virtualization that isolates different groups of applications that operate in different containers. Such containers are more lightweight than VMs. 
     Hypervisor kernel network interface modules, in some embodiments, is a non-VM DCN that includes a network stack with a hypervisor kernel network interface and receive/transmit threads. One example of a hypervisor kernel network interface module is the vmknic module that is part of the ESXi™ hypervisor of VMware, Inc. 
     One of ordinary skill in the art will recognize that while the specification refers to VMs, the examples given could be any type of DCNs, including physical hosts, VMs, non-VM containers, and hypervisor kernel network interface modules. In fact, the example networks could include combinations of different types of DCNs in some embodiments. 
     IV. Electronic System 
     Many of the above-described features and applications are implemented as software processes that are specified as a set of instructions recorded on a computer readable storage medium (also referred to as computer readable medium). When these instructions are executed by one or more processing unit(s) (e.g., one or more processors, cores of processors, or other processing units), they cause the processing unit(s) to perform the actions indicated in the instructions. Examples of computer readable media include, but are not limited to, CD-ROMs, flash drives, RAM chips, hard drives, EPROMs, etc. The computer readable media does not include carrier waves and electronic signals passing wirelessly or over wired connections. 
     In this specification, the term “software” is meant to include firmware residing in read-only memory or applications stored in magnetic storage, which can be read into memory for processing by a processor. Also, in some embodiments, multiple software inventions can be implemented as sub-parts of a larger program while remaining distinct software inventions. In some embodiments, multiple software inventions can also be implemented as separate programs. Finally, any combination of separate programs that together implement a software invention described here is within the scope of the invention. In some embodiments, the software programs, when installed to operate on one or more electronic systems, define one or more specific machine implementations that execute and perform the operations of the software programs. 
       FIG. 10  conceptually illustrates an electronic system  1000  with which some embodiments of the invention are implemented. The electronic system  1000  can be used to execute any of the control, virtualization, or operating system applications described above. The electronic system  1000  may be a computer (e.g., a desktop computer, personal computer, tablet computer, server computer, mainframe, a blade computer etc.), phone, PDA, or any other sort of electronic device. Such an electronic system includes various types of computer readable media and interfaces for various other types of computer readable media. Electronic system  1000  includes a bus  1005 , processing unit(s)  1010 , a system memory  1025 , a read-only memory  1030 , a permanent storage device  1035 , input devices  1040 , and output devices  1045 . 
     The bus  1005  collectively represents all system, peripheral, and chipset buses that communicatively connect the numerous internal devices of the electronic system  1000 . For instance, the bus  1005  communicatively connects the processing unit(s)  1010  with the read-only memory  1030 , the system memory  1025 , and the permanent storage device  1035 . 
     From these various memory units, the processing unit(s)  1010  retrieves instructions to execute and data to process in order to execute the processes of the invention. The processing unit(s) may be a single processor or a multi-core processor in different embodiments. 
     The read-only-memory (ROM)  1030  stores static data and instructions that are needed by the processing unit(s)  1010  and other modules of the electronic system. The permanent storage device  1035 , on the other hand, is a read-and-write memory device. This device is a non-volatile memory unit that stores instructions and data even when the electronic system  1000  is off. Some embodiments of the invention use a mass-storage device (such as a magnetic or optical disk and its corresponding disk drive) as the permanent storage device  1035 . 
     Other embodiments use a removable storage device (such as a floppy disk, flash drive, etc.) as the permanent storage device. Like the permanent storage device  1035 , the system memory  1025  is a read-and-write memory device. However, unlike storage device  1035 , the system memory is a volatile read-and-write memory, such a random access memory. The system memory stores some of the instructions and data that the processor needs at runtime. In some embodiments, the invention&#39;s processes are stored in the system memory  1025 , the permanent storage device  1035 , and/or the read-only memory  1030 . From these various memory units, the processing unit(s)  1010  retrieves instructions to execute and data to process in order to execute the processes of some embodiments. 
     The bus  1005  also connects to the input and output devices  1040  and  1045 . The input devices enable the user to communicate information and select commands to the electronic system. The input devices  1040  include alphanumeric keyboards and pointing devices (also called “cursor control devices”). The output devices  1045  display images generated by the electronic system. The output devices include printers and display devices, such as cathode ray tubes (CRT) or liquid crystal displays (LCD). Some embodiments include devices such as a touchscreen that function as both input and output devices. 
     Finally, as shown in  FIG. 10 , bus  1005  also couples electronic system  1000  to a network  1065  through a network adapter (not shown). In this manner, the computer can be a part of a network of computers (such as a local area network (“LAN”), a wide area network (“WAN”), or an Intranet, or a network of networks, such as the Internet. Any or all components of electronic system  1000  may be used in conjunction with the invention. 
     Some embodiments include electronic components, such as microprocessors, storage and memory that store computer program instructions in a machine-readable or computer-readable medium (alternatively referred to as computer-readable storage media, machine-readable media, or machine-readable storage media). Some examples of such computer-readable media include RAM, ROM, read-only compact discs (CD-ROM), recordable compact discs (CD-R), rewritable compact discs (CD-RW), read-only digital versatile discs (e.g., DVD-ROM, dual-layer DVD-ROM), a variety of recordable/rewritable DVDs (e.g., DVD-RAM, DVD-RW, DVD+RW, etc.), flash memory (e.g., SD cards, mini-SD cards, micro-SD cards, etc.), magnetic and/or solid state hard drives, read-only and recordable Blu-Ray® discs, ultra density optical discs, any other optical or magnetic media, and floppy disks. The computer-readable media may store a computer program that is executable by at least one processing unit and includes sets of instructions for performing various operations. Examples of computer programs or computer code include machine code, such as is produced by a compiler, and files including higher-level code that are executed by a computer, an electronic component, or a microprocessor using an interpreter. 
     While the above discussion primarily refers to microprocessor or multi-core processors that execute software, some embodiments are performed by one or more integrated circuits, such as application specific integrated circuits (ASICs) or field programmable gate arrays (FPGAs). In some embodiments, such integrated circuits execute instructions that are stored on the circuit itself. 
     As used in this specification, the terms “computer”, “server”, “processor”, and “memory” all refer to electronic or other technological devices. These terms exclude people or groups of people. For the purposes of the specification, the terms display or displaying means displaying on an electronic device. As used in this specification, the terms “computer readable medium,” “computer readable media,” and “machine readable medium” are entirely restricted to tangible, physical objects that store information in a form that is readable by a computer. These terms exclude any wireless signals, wired download signals, and any other ephemeral signals. 
     While the invention has been described with reference to numerous specific details, one of ordinary skill in the art will recognize that the invention can be embodied in other specific forms without departing from the spirit of the invention. In addition, a number of the figures (including  FIGS. 6 a - b   ) conceptually illustrate processes. The specific operations of these processes may not be performed in the exact order shown and described. The specific operations may not be performed in one continuous series of operations, and different specific operations may be performed in different embodiments. Furthermore, the process could be implemented using several sub-processes, or as part of a larger macro process. Thus, one of ordinary skill in the art would understand that the invention is not to be limited by the foregoing illustrative details, but rather is to be defined by the appended claims.