Patent Publication Number: US-2006013248-A1

Title: Switching device interfaces

Description:
BACKGROUND OF THE INVENTION  
      This invention relates generally to interfaces on a network device.  
      Network devices have physical interfaces that are subject to failure. When such an interface fails, a network device can be cut-off from the network. This is particularly problematic in the case of a router, where failure of a single physical interface can make a whole branch of the network inaccessible to other devices.  
     SUMMARY OF THE INVENTION  
      In one aspect of the invention, a device is switched from a first physical interface on the device (for example, a failed interface) to a second physical interface on the device based on information in an interface redundancy group. The information in the interface redundancy group identifies the first physical interface as a primary interface for the device and the second physical interface as a secondary interface for the device.  
      The foregoing aspect of the invention may include one or more of the following features/functions.  
      The interface redundancy group may include information defining the primary interface for the device and one or more secondary interfaces for the device. An event may be detected at the first physical interface, and switching may be performed in response to the event. The event may comprise a failure of the first physical interface. The first physical interface may be associated with a driver and a signaling stack, and the failure of the first physical interface may comprise a failure of the driver and/or the signaling stack. The driver and the signaling stack may be monitored in order to detect failures therein. The event may comprise receipt of a slot failure at the first physical interface.  
      Prior to switching, the second physical interface may operate in a passive mode during which the second physical interface is dormant. Prior to switching, the second physical interface may operate in an active mode during which the second physical interface is communicating over a network. The first physical interface may support one or more network layer interfaces. Following switching, the second physical interface may support the one or more network layer interfaces formerly supported by the first physical interface. The first and second physical interfaces may comprise asynchronous transfer mode (“ATM”) physical interfaces. The first and second physical interfaces may be resident on a single network router.  
      Following switching, the second physical-interface may assume responsibilities of the first physical interface. These responsibilities may include routing and/or bridging functions. Following switching, the second physical interface may be configured in a same manner as the first physical interface was configured prior to switching. The device may include a third physical interface, and the interface redundancy group may identify the third physical interface as a tertiary interface. The device may be switched from the second physical interface to the third physical interface in response to an event. Following switching, the third physical interface may assume responsibilities of the first and second physical interfaces. These responsibilities may include routing and/or bridging functions.  
      In another aspect, physical interfaces on a single device are switched by designating a physical interface on the device as a high priority physical interface, and determining if the high priority physical interface is available. The device is switched from a lower priority physical interface to the high priority physical interface when the high priority physical interface is available.  
      The foregoing aspect of the invention may include one or more of the following features/functions. Switching may be performed automatically in response to the high priority interface being available. The high priority physical interface may be monitored to determine if the high priority physical interface is available.  
      In another aspect, a device is switched from a first ATM physical interface on the device to a second ATM physical interface on the device based on information in an interface redundancy group. The information in the interface redundancy group identifies the first ATM physical interface as a primary interface for the device and the second ATM physical interface as a secondary interface for the device. ATM network layer interfaces are established over the second physical interface that correspond to ATM network layer interfaces that were established over the first ATM physical interface prior to switching.  
      This brief summary has been provided so that the nature of the invention can be understood quickly. A detailed description of illustrative embodiments of the invention is set forth below.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  shows a network system, which includes a router having switchable physical interfaces.  
       FIG. 2  shows virtual circuits supported by the physical interfaces on the router.  
       FIG. 3  is a flow diagram showing a process for switching a physical interface on the router in “passive” mode.  
       FIG. 4  shows an alternative connection of the virtual circuits to the physical interfaces on the router.  
       FIG. 5  is a flow diagram showing a process for switching a physical interface on the router in “active” mode.  
       FIG. 6  shows the configuration of the virtual circuits after the switching performed in  FIG. 5 .  
       FIG. 7  is a flow diagram showing a process for switching a physical interface on the router based on priority.  
       FIG. 8  shows a router having three physical interfaces and redundancy groups therefor. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
      Referring to  FIG. 1 , a network system  10  is shown. Network system  10  includes router  12 , switches  14  and  16 , workstations  18 ,  20  and  22 , and network  24 .  
      Network  24  is an asynchronous transfer mode (“ATM”) wide area network (“WAN”). ATM is a connection-oriented protocol, meaning that connections are established between devices before data and/or communications can be transmitted between the devices. The network layer interface comprises virtual circuits, over which data packets (in ATM parlance, “cells”) are transmitted among devices coupled to network  24 , such as router  12  and switches  14  and  16 . Virtual circuits can be established by protocols such as ELANs (Emulated Local Area Networks) on network  24 .  
      Switches  14  and  16  interface workstations  20  and  22 , respectively, to network  24 . Each switch  14  and  16  is an electronic device that routes cells between network  24  and a corresponding workstation. Workstations  18 ,  20  and  22  are personal computers (“PCs”) or other devices that are capable of receiving cells from network  24 , processing cells, and transmitting cells to network  24 .  
      Router  12  is a computer or other device that transmits packets/cells among workstations  18 ,  20  and  22  via network  24 . For example, router  12  receives cells/packets from workstation  18  and, based on information in those cells/packets, routes the cells/packets to either workstation  20  or  22  (through an intervening switch and other hardware on network  24 ).  
      ATM physical interfaces  26   a  and  26   b  are ports provided on router  12  for interfacing to network  24 . Although only two such interfaces are shown, any number may be provided. In system  10  of  FIG. 1 , one of the interfaces (e.g.,  26   a ) is designated as the primary interface for router  12  and the other (e.g.,  26   b ) is designated as the secondary (or backup) interface. When the primary physical interface  26   a  fails, the secondary physical interface.  26   b  is switched in to take its place. A process to accomplish this is described below.  
      Physical interfaces  26   a  and  26   b  are comprised of wires terminating in connectors, such as an OC-3/OC-12 connector, which mate to corresponding receptacles on router  12 . One or more network layer interfaces are established by router  12  over each physical interface  26   a  and  26   b  for communication to, and over, network  24 . ATM line drivers  30   a  and  30   b  transmit cells over corresponding physical interfaces  26   a  and  26   b.    
      Included in router  12  are a processor  34  and a memory  36  connected by bus  38  (see view  40 ). Memory  36  stores routing engines  42   a  and  42   b , interface switching code  44 , and signaling stacks  46   a  and  46   b . Processor  34  executes instructions in this code to cause router  12  to perform the functions described below. Memory  36  also stores interface redundancy group information  48  (described below).  
      Signaling stacks  46   a  and  46   b  are blocks of code, associated with corresponding physical interfaces  26   a  and  26   b , for establishing virtual connections for the network layer interfaces over the physical interfaces. As noted, one or more network layer interfaces may be configured over a single ATM physical interface  26   a  and  26   b.    
      Routing engine  42   a  routes cells over physical interface  26   a  and routing engine  42   b  routes cells over physical interface  26   b . Routing engines  42   a  and  42   b  examine destination information in the cells and route the cells over appropriate interfaces. Examples of routing engines that may be used are “ARE” (ATM Routing Engine) and the 5782 Centillion Multiprotocol Engine.  
      Interface redundancy group information  48  defines which physical interface is the primary interface (e.g.,  26   a ) and which is the secondary interface (e.g.,  26   b ). This information may be input manually at router  12  via configuration software such as Site Managers or Bay Command Consoles (“BCC”). This software is used by network administrators to configure network devices. Alternatively, interface redundancy group information  48  may be downloaded from a remote location such as network  24  or workstation  18  or set via interface switching code  44 .  
      Interface redundancy group information  48  includes user-defined redundancy groups. These redundancy groups assign priority to the interfaces. In the case of a two-interface router, such as router  12 , there are two possible groups. For example, physical interface  26   a  is configured as the primary interface and physical interface  26   b  is configured as the secondary interface. The routing engine for each interface is configured to know the role of the interface in each redundancy group. Representative code to configure routing engines is provided in the Appendix.  
      In routers with more than two physical interfaces, interface redundancy groups become more complicated. Table 1 shows an example of redundancy groups for a router having four physical interfaces “Interface 1”, “Interface 2”, “Interface 3” and “Interface 4” (not shown).  
                                   TABLE 1                                   Redundancy   Primary   Secondary   Tertiary           Group   Interface   Interface   Interface                                                            1   Interface 1   Interface 2   Interface 3           2   Interface 2   Interface 1   Interface 3           3   Interface 4   Interface 3   —                      
 
 For example, in redundancy group “1”, “Interface 1” acts as the primary interface; “Interface 2” acts as the secondary (first backup) interface and is used if. “Interface 1” fails; and “Interface 3” acts as the tertiary (or second backup) interface and is used if both “Interfaces 1” and “Interface 2” fail. 
 
      Detecting physical interface failure and switching from a primary to a secondary physical interface (or from a secondary to a tertiary physical interface, etc.) is performed by interface switching code  44 . The operation of interface switching code  44  differs depending upon whether the secondary interface is in passive mode or active mode.  
      Passive Mode  
      In passive mode, prior to switching, the secondary interface is dormant. That is, the secondary interface is not driving/receiving signals to/from network  24 . Passive mode may be set as the default mode of router  12  using Site Manager® or BCC®.  
      Referring to  FIG. 2 , a graphical representation of passive mode is shown. In  FIG. 2 , physical interface  26   a  is configured as the primary interface and physical interface  26   b  is configured as the secondary interface in passive mode. This configuration is set in interface redundancy group information  48 . In  FIG. 2 , lines  54   a  to  54   h  represent connections maintained by primary physical interface  26   a  and lines  56   a  to  56   h  represent connections that are maintained by secondary physical interface  26   b  after secondary interface  26   b -takes over the role of primary interface  26   b.    
      Referring to  FIG. 3 , an interface switching process  56  is shown. Interface switching process  56  is performed by interface switching code  44  to switch from primary physical interface  26   a  to secondary physical interface  26   b . Process  56  monitors  58  primary physical interface  26   a , including both driver  30   a  and signaling stack  46   a , for specific “events”. These events can include, but are not limited to, receipt of a slot reset at primary physical interface  26   a  and/or a failure of primary physical interface  26   a , such as a failure of driver  30   a  and/or signaling stack  46   a.    
      In response to detecting  60  one of the foregoing events, process  56  switches  62  from primary physical interface  26   a  to secondary physical interface  26   b  (in accordance with interface redundancy group information  48 ). Switching  62  is performed by enabling driver  30   b  for secondary physical interface  26   b . Following switching, secondary interface  26   b  establishes  63  the network layer interfaces to network  24  (in this example, ELANs  52   a  to  52   h ), and assumes the responsibilities (including routing and bridging services) of primary interface  26   b . Switching between interfaces is performed as quickly as possible, e.g., within thirty seconds of failure or reset.  
      With driver  30   b  enabled, in  64 , signaling stack  46   b  transmits cells over secondary physical interface  26   b  to ELANs  52   a  to  52   h . Primary physical interface  26   a  can be repaired while secondary physical interface  26   b  performs its functions.  
      Active Mode  
      In active mode, prior to switching, the secondary physical interface  26   b  is already communicating over the network. Following failure of the primary physical interface  26   a , the secondary interface  26   b  assumes the responsibilities of the primary interface  26   a . In particular, upon switching, code in the signaling stack establishes the network layer interfaces (e.g., over ELANs) of the primary interface  26   a , and assumes the routing and bridging functions of the primary interface  26   a.    
      Referring to  FIG. 4 , a graphical representation of active mode is shown. In  FIG. 4 , physical interface  26   a  is the primary interface and physical interface  26   b  is the secondary interface in active mode. This configuration is set in interface redundancy group information  48 . Since secondary physical interface  26   b  is in active mode, prior to switching, it is providing network layer services over virtual circuits for ELANs  52   e  to  52   h . Primary physical interface  26   a  is supporting ELANs  52   a  to  52   d.    
      Referring to  FIG. 5 , an interface switching process  66  is shown, that is performed by interface switching code  44  to switch from primary physical interface  26   a  to secondary physical interface  26   b . Interface switching process  66  monitors  68  primary physical interface  26   a , including both driver  30   a  and signaling stack  46   a , for specific events. These events are the same as those noted above for passive mode.  
      In response to detecting  70  one of the foregoing events, process  66  switches  72  from primary physical interface  26   a  to secondary physical interface  26   b . Switching is performed in the manner described above; that is, enabling and disabling the drivers for the appropriate network interfaces.  
      Interface switching process  66  establishes  74 , over secondary physical interface  26   b , the network layer interfaces (in this case, ELANs  52   a  to  52   d ) of primary physical interface  26   a . Secondary physical interface  26   b  continues to perform its original routing and bridging functions over ELANs  52   e  to  52   h . Now, however, secondary physical interface  26   b  also performs the routing and bridging functions formerly performed by primary physical interface  26   a  over ELANs  52   a  to  52   d.    
      With driver  30   b  enabled, and secondary physical interface  26   b  switched, in  76 , signaling stack  46   b  transmits cells over secondary physical interface  26   b  to all of ELANs  52   a  to  52   h . This is shown in  FIG. 6 . Primary physical interface  26   a  no longer transmits (hence no lines are shown between this interface and the ELANs in  FIG. 6 ).  
      Switching Based on Priority  
      ATM physical interfaces may also be assigned relative priorities and switched on that basis. An option in router.  12  may be set, e.g., by a user, to trigger automatic switching based on priority. The priority information upon which switching is based may be included in interface redundancy group information  48 , for example.  
      Referring to  FIG. 7 , a process  78  is shown that is performed by interface switching code  44  to switch interfaces based on priority. Process  78  designates  80  any number of physical interfaces on a sliding priority scale, from highest priority to lowest priority. In router  12  ( FIG. 2 ), only two physical interfaces are shown. For the sake of illustration, therefore, physical interface  26   a  is designated  80  as high priority and physical interface  26   b  is designated  80  as low priority.  
      Once physical interfaces  26   a  and  26   b  are designated in terms of priority, switching between them may be performed. Process  78  monitors  82  high priority physical interface  26   a  to determine if it is up and running. If high priority physical interface  26   a  is available  84  (i.e., it is not “down”), process  78  switches  86  from low priority physical interface  26   b  to high priority physical interface  26   a . As a result, the “best available” interface on router  12  is used to provide network layer connections over network  24 . Process  60  may be incorporated into processes  56  and  66  to provide further enhanced switching capabilities.  
      As noted above, the invention may be used on routers having more than two physical interfaces. For example, in  FIG. 8 , router  90  has three physical interfaces  92   a ,  92   b  and  92   c  organized into two interface redundancy groups  94  and  96 . Interfaces  92   a  and  92   c  are in group  94  and interfaces  92   b  and  92   c  are in group  96 . In this example, interface  92   c  is a backup for interfaces  92   a  and  92   b . If either of interfaces  92   a  and  92   b  fail, then interface  92   c  will assume the configuration of either (or both of) failed interfaces  92   a  and  92   b.    
      Switching in the case of more than two interfaces is performed in the same way as described in processes  56 ,  66  and  78 , except that a decision must be made regarding which (lower priority) interface to switch for the primary interface. This decision is made based on interface availability and the priority of the various interfaces.  
      The invention is not limited to the specific hardware and software configurations described herein. For example, the invention can be used outside the context of ATM WANs, and with network devices other than routers. In this regard, it is to be understood that while the invention has been described in conjunction with the detailed description thereof, the foregoing description is intended to illustrate, and not to limit, the scope of the invention. Other aspects, advantages, and modifications are within the scope of the following claims.