Patent Publication Number: US-7716366-B2

Title: Enhancement of VRRP interface and router selection where an non-owner router is configured to respond to control and management messages addressed to an address associated with the virtual redundant router

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application claims priority to U.S. Provisional Patent Application No. 60/466,323 entitled “Enhanced virtual router redundancy protocol” filed Apr. 28, 2003 which is incorporated herein by reference for all purposes. 

   FIELD OF THE INVENTION 
   The present invention relates generally to computer networks. More specifically, an enhanced virtual router redundancy protocol is disclosed. 
   BACKGROUND OF THE INVENTION 
   The Virtual Router Redundancy Protocol (VRRP) provides for the implementation of a redundant IP interface to be shared between two or more routers on a common LAN segment. VRRP is described in IETF RFC 2338. VRRP allows you to provide alternate router paths for a host without changing the IP address or MAC address by which the host knows its gateway. The use of virtual routers, or abstract objects that may include one or more physical routers, enables failover redundant routing in the event a master router fails due to non-availability or another type of event. However, the existing protocol suffers from various limitations. 
   In VRRP control and management abilities (e.g., the ability to respond to ICMP ping, TCP connection requests, etc.) are limited to owner routers. Routers are classified as owners and non-owners, where owners “own” an actual IP address for the interface or gateway to a LAN, WAN, MAN, LAN segment, etc. This means that only owners may respond to management-oriented protocols such as ICMP ping. If the owner router fails, is taken out of service, or otherwise becomes unavailable, then no router, including a non-owner router that takes over as the master router for the virtual router identifier (VRID) with which the IP address used for the virtual router is associated, will respond to management-oriented messages, such as those used for testing connectivity (e.g., ICMP Ping). If a backup non-owner router is assigned as the new master router, it will not respond to messages sent to the IP address associated with the virtual router identifier for which it has taken over as master because that IP address is an actual interface only on the owner. Thus, system and network administrators are unable to gather information as to whether a particular gateway has connectivity. More problematic is the master selection process specified in VRRP. 
   VRRP does not specify events or conditions that determine how a master is selected from non-owner routers. When a master router fails, VRRP provides for the next specified non-owner router to become master. However, this fails to take into account events or network conditions that could affect whether a particular non-owner router is better suited to become master over another. This may lead to the inefficient selection of backup non-owner routers as master routers. 
   Thus, a solution is needed for an improved virtual router redundancy protocol for selecting a master router. Additionally, a solution is required that enables master router selection based on criteria such as availability and priority. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Various embodiments of the invention are disclosed in the following detailed description and the accompanying drawings. 
       FIG. 1  illustrates an exemplary system for implementing an enhanced virtual router redundancy protocol; 
       FIG. 2  illustrates an exemplary system for implementing an enhanced virtual router redundancy protocol when a master router fails; 
       FIG. 3  illustrates an exemplary process for applying a priority control priority to select a master router; 
       FIG. 4  illustrates an exemplary priority control process using explicit priority values; 
       FIG. 5  illustrates an exemplary priority control process using delta priority values; and 
       FIG. 6  illustrates an exemplary master router selection process. 
   

   DETAILED DESCRIPTION 
   The invention can be implemented in numerous ways, including as a process, an apparatus, a system, a composition of matter, a computer readable medium such as a computer readable storage medium or a computer network wherein program instructions are sent over optical or electronic communication links. In this specification, these implementations, or any other form that the invention may take, may be referred to as techniques. In general, the order of the steps of disclosed processes may be altered within the scope of the invention. 
   A detailed description of one or more embodiments of the invention is provided below along with accompanying figures that illustrate the principles of the invention. The invention is described in connection with such embodiments, but the invention is not limited to any embodiment. The scope of the invention is limited only by the claims and the invention encompasses numerous alternatives, modifications and equivalents. Numerous specific details are set forth in the following description in order to provide a thorough understanding of the invention. These details are provided for the purpose of example and the invention may be practiced according to the claims without some or all of these specific details. For the purpose of clarity, technical material that is known in the technical fields related to the invention has not been described in detail so that the invention is not unnecessarily obscured. 
   An enhanced virtual router redundancy protocol is disclosed. In some embodiments, the enhancements provide a degree of control over the backup router priority values used to determine which backup router will take over as master in the event the owner/master fails or otherwise becomes unavailable. Router, as used herein, may refer to a virtual router comprising a master router and one or more backup routers associated with the same virtual router identifier (VRID). Selecting a master router based on backup router priorities determined at least in part by applying a priority control policy to one or more of the backup routers is disclosed. The priority control policy and priority values may be used to adjust a backup router&#39;s priority based on network conditions and events (hereinafter referred to as “event” or “events”) that may affect the router&#39;s availability, efficiency, or effectiveness in the role as master. In some embodiments, explicit priority values may be specified to indicate the explicit priority level to which a backup router should be set if a corresponding event should occur. In some embodiments, delta priority values may be used to decrement or increment a base priority for a particular backup router. In some embodiments, explicit priority values may override delta priority values. If no explicit priority values are provided, then delta priority values may be used to derive an overall priority for a backup router. By using priority control policies and priority values to select a master from among backup/non-owner routers associated with the same VRID, improved control and manipulation of virtual router instances are enabled. 
     FIG. 1  illustrates an exemplary system  100  for implementing an enhanced virtual router redundancy protocol. A network  100  is shown having several routers and hosts attached. Master router  102 , backup router  104 - 106  may be associated with a virtual router instance that acts as a gateway or interface for routing data (e.g., packets, segments, frames, etc.). In this example, master router  102  and backup routers  104 - 106  are connected to network  108 , which has hosts  110 - 118 . Network  108  may be a LAN, LAN segment, or other type of network besides those mentioned herein. Data sent to hosts  110 - 118  are routed through master router  102  over network  108 . Similarly, data sent by hosts  110 - 118  to destinations beyond network  108  (e.g., the Internet, or an intranet) may be sent via master router  102  acting, e.g., as a default gateway to such destinations beyond network  108 . 
   To provide redundancy, without requiring that the hosts  110 - 118  be reconfigured with different default gateway information in the event the master router  102  becomes unavailable, the virtual router redundancy protocol (VRRP) provides a way to define a virtual router comprising, e.g., master router  102  and backup routers  104 - 106 . The routers  102 - 106  may each be associated with the same VRID, which VRID is in turn associated with, e.g., an actual IP interface owned by router  102 . The hosts  110 - 118  may then be configured to use the virtual router represented by the VRID as their default gateway. If the master/owner router  102  becomes unavailable, one of the backup routers  104  or  106  becomes master and begins to handle traffic sent to the IP address/MAC address associated with the VRID, even though the non-owner/master (i.e., the former backup that has become master) does not actually own the IP address associated with the VRID. 
   Each router may also be classified as an owner or non-owner. An owner router “owns” as an actual IP interface of the owner router the IP address associated with the VRID of the virtual router. As such, the owner router always responds to control and management messages, such as ICMP echo requests, ping requests, etc., so long as it is online and able to receive and respond to such messages. A non-owner normally would not respond to such control and management messages sent to the IP address associated with the VRID, even when not as a master router, because the IP address associated with the VRID is not an actual IP interface of the non-owner router(s). However, in some embodiments, system  100  may be configured to enable non-owner routers to respond to control and management messages sent to the IP address associated with the VRID of the virtual router at a time when the non-owner is serving as master. In other words, this restraint in VRRP may be overridden using the enhanced protocol described herein. This enables administrators to use well-known techniques, e.g., ICMP Ping, to test connectivity to their default gateway using the IP address and MAC address associated with the virtual router, and receive a reply even if a non-owner router is acting as master for the VRID. In the example shown in  FIG. 1 , each router has a priority value associated with it. For example, master router  102  has a priority value of  255 , which is the priority level prescribed by the VRRP for an owner router and the highest possible priority value under the protocol. This ensures that if the owner is available, it becomes the master. Backup routers  104  and  106  each have an initial priority value of  100 , the initial priority value prescribed by VRRP for non-owner routers. 
     FIG. 2  illustrates an exemplary system  200  for implementing an enhanced virtual router redundancy protocol. In the example shown, the original master router, owner router  202 , has failed or otherwise become unavailable, as indicated by the large “X” below owner router  202 . Under VRRP, one way that owner router  202  may be removed from the role of master absent a failure, e.g., to perform maintenance on or reconfigure the owner router, is to manual set its priority to 0, as shown in  FIG. 202 . Non-owner routers  204  and  206  remain connected to network  208 . In the example shown, non-owner routers have determined, based on their respective priorities at the time the original master  202  became unavailable (shown in this example as being 100 for non-owner router  204  and 80 for non-owner router  206 ), that non-owner router  204  will act as master and non-owner router  206  will continue to serve as a backup, because non-owner router  204  had the higher priority. When hosts  210 - 218  send data via network  208  to their default gateway, using the same IP and MAC address as they used when owner router  202  was serving as master, new master router  204  will process and forward the packets, thereby providing continuing connectivity to networks (e.g., the Internet) beyond network  208  without requiring any change to the configuration of hosts  210 - 218 . 
     FIG. 3  illustrates an exemplary process for applying a priority control policy to adjust a priority value on a non-owner router. As an example, a priority control policy may be used to adjust on each of a plurality of non-owner routers associated with a VRID the “in use” priority of the non-owner router. Under VRRP, the adjusted in use priorities of the respective non-owner routers is used to arbitrate between them to determine which router becomes master in the event a current master router fails, becomes unavailable, loses connectivity, etc. A priority control policy is applied to non-owner routers ( 302 ). The priority control policy specifies how to determine priority values for non-owner routers. In some embodiments, as described more fully below, step  302  comprises adjusting an in use priority level from an initial base priority of 100 in response to the occurrence of an event defined in a priority control policy associated with the non-owner router. In some embodiments, events may either be associated with an explicit priority value (e.g., 80) or an amount by which the in use priority should be decremented or, in some embodiments, incremented. In the event the current master router becomes unavailable, a new master router is selected based on the respective priorities of the available non-owner routers as adjusted based on their respective priority control policies ( 304 ). In some embodiments, one or more non-owner routers may have a priority control policy that is different from the priority control policy applied to one or more other non-owner routers associated with the same VRID. 
   In some embodiments, the priority of a router may be determined under a priority control policy either by setting the priority level to an explicit level associated with an event defined in the policy (sometimes referred to below as an “explicit” type priority event), or by decrementing (or, in some embodiments, incrementing) the in use priority by an amount associated with such an event (sometimes referred to below as a “delta” type priority event). Each event generates a VRRP priority event message. Priority event messages include information that may be used to determine the priority of a non-owner router. This information includes a policy identifier (policy-id) that identifies the priority control policy with which the event is associated, an event type (examples provided below), a priority type (explicit or delta, both of which are described more fully in  FIGS. 4 and 5 ), and an event priority value. In this embodiment, the event priority value is expressed numerically. In other embodiments, the event priority value may be expressed in alternative forms (e.g., on or off, 1 or 0, an arbitrarily defined code or value, etc.). Additionally, less or more information than that described above may be included. 
   As discussed above, priority events include information that identifies a priority type and value, either an explicit priority value or a delta priority value. Events that may affect priority may be referred to as priority events. Examples of priority events include port down, LAG degrade, host unreachable, route unknown, OSPF down, IS-IS down, LDP down, TLDP down, BGP down, LSP down, or other indications that may affect the ability to route packets to one or more destinations. These and/or other or different events may be defined in the priority control policy. Events may be generated based on conditions or occurrences local to the router or based on remote conditions or information (e.g., reachability). Explicit priority values are those that define a set priority value for a router. The process of using explicit priority values to set the priority of a router is described in connection with  FIG. 4 . In contrast, delta priority values are values used to decrement or increment a base priority value. 
   A base priority value provides for a priority value that is either replaced by an explicit priority value or modified by a delta priority value. Delta priority values may either increment or decrement the base priority value to yield an adjusted in use priority value. As a result, the in use priority of each non-owner router on which a priority control policy has been implemented may change over time and explicit type and delta type events occur. In the embodiment illustrated in  FIG. 4  and described more fully below, e.g., explicit priority values override delta priority values. However, in other embodiments, delta priority values may override explicit priority values or the two may be handled equally. The process for using delta priority values to adjust the in use priority of a non-owner router is described in greater detail below in connection with  FIG. 5 . In either case, the base priority value may have upper and lower limits that can be specified in the protocol, by a user, or set automatically to a default value. In one embodiment, the in use priority may not be decrement to be less than 1, to prevent a non-owner router from being rendered operationally unavailable. 
     FIG. 4  illustrates an exemplary priority control process. In this example, explicit priority values are set values associated with a specified event or condition. In some embodiments, explicit values may override a delta priority value. In the process shown in  FIG. 4 , a priority event is detected ( 402 ). A determination is made as to whether an explicit priority value is associated with the event detected in  FIG. 402  and/or any previously detected event or condition ( 404 ). If there are no explicit priority values, then delta priority values are used to determine the in use priority ( 406 ). When delta priority values are used, as in step  406 , the in-use priority value is set by decrementing or incrementing a base value, as described more fully below in connection with  FIG. 5 . 
   If it is determined in step  404  that an explicit priority value is present, e.g., because the event detected in step  402  and/or a previously-detected event or condition that is still present or relevant has an explicit priority value associated with it, then a check is performed to determine whether multiple explicit priority values exist( 410 ), i.e., whether there are multiple events or conditions that have explicit values associated with them. For example, a previously generated Port Down priority event may have associated with it a first explicit priority of 80 and a subsequently received OSPF Down priority event, received while the port that generated the Port Down priority event is still down, may have associated with it a second explicit priority of 60. In such a case, it would be determined in step  410  that multiple explicit priority values are present. If multiple explicit priority values are present, then the lowest explicit priority value is set as the priority value for the evaluated router ( 412 ), after which the process ends. If multiple explicit priority values are not detected ( 410 ), i.e., there is only one currently applicable event or condition that has an explicit priority value associated with it, then the in use priority for the router is set to the explicit value ( 411 ), after which the process ends. 
     FIG. 5  illustrates a process for setting an in use priority value using delta priority values. The process of  FIG. 5  is used in some embodiments to implement step  406  of  FIG. 4 . Here, a base priority for the router is determined ( 502 ). Delta priority values are retrieved for the router ( 504 ). These may comprise a delta value for the most recently detected event and/or one or more delta values associated with previously-detected but still present and/or otherwise relevant events or conditions. An in use priority value is then created for the affected router ( 506 ). In some embodiments, multiple priority events may be applicable to a router. This may require applying multiple delta priority values to a base priority value. 
   In some embodiments, if multiple delta type events or conditions are present, the respective delta values are combined and then applied to the base priority to calculate an adjusted in use priority. In other embodiments, delta or explicit priorities are applied as the events that generated them occur, and a subsequently received delta is applied to the previously-adjusted in use priority, such that the cumulative effect of the events is reflected in the in use priority. 
     FIG. 6  illustrates an exemplary master router selection process. In this example, a determination is made as to whether the IP address owner (for the given interface) is available ( 602 ). If the owner router is available, then it is assigned as the master router ( 604 ). In some embodiments, this results from the fact that the owner is configured to have a priority of 255, the highest possible value and higher than the range permitted for non-owner routers (typically from 1 or some other very low value to 254). However, if the owner router is unavailable, then a master router is selected from among the non-owner backup routers by evaluating the priority values, as described above in connection with  FIGS. 3-5  ( 606 ). The selection of non-owner routers using the techniques described above provides for a granular ability to manipulate the criteria, conditions, and events that define a non-owner router&#39;s candidacy for master router. Such manipulation enables greater control and management of data routing using protocols such as VRRP. 
   Although the foregoing embodiments have been described in some detail for purposes of clarity of understanding, the invention is not limited to the details provided. There are many alternative ways of implementing the invention. The disclosed embodiments are illustrative and not restrictive.