WIXLIB

CHAPTER 5High AvailabilityThis chapter provides information and commands concerning the following topics: Hot Standby Routing Protocol (HSRP)— Configuring HSRP— Verifying HSRP— HSRP optimization options— Debugging HSRP Virtual Router Redundancy Protocol (VRRP)— Configuring VRRP— Verifying VRRP— Debugging VRRP Gateway Load Balancing Protocol (GLBP)— Configuring GLBP— Verifying GLBP— Debugging GLBPHot Standby Routing ProtocolThe Hot Standby Router Protocol (HSRP) provides network redundancy for IPnetworks, ensuring that user traffic immediately and transparently recovers from firsthop failures in network edge devices or access circuits.Configuring HSRPinterfaceRouter(config)#ifastethernet 0/0Moves to interface configuration modeipRouter(config-if)#iaddress 172.16.0.10255.255.255.0Assigns IP address and netmaskstandbyRouter(config-if)#s1 ip 172.16.0.1Activates HSRP group 1 on the interface and createsa virtual IP address of 172.16.0.1 for use in HSRPNOTE: The group number can be from 0 to 255.The default is 0.standbyRouter(config-if)#s1 priority 120Assigns a priority value of 120 to standby group 1

60Hot Standby Routing ProtocolNOTE: The priority value can be from 1 to 255. Thedefault is 100. A higher priority will result in thatrouter being elected the active router. If the prioritiesof all routers in the group are equal, the router withthe highest IP address becomes the active router.Verifying HSRPshow running-configRouter#sDisplays what is currently running onthe routershow standbyRouter#sDisplays HSRP informationshow standby briefRouter#sDisplays a single-line output summaryof each standby groupshow standby 1Router#sDisplays HSRP group 1 informationshow standby fastethernet 0/0Router#sDisplays HSRP information for thespecified interfaceshow standby fastethernet 0/0Router#sbriefDisplays a summary of HSRP for thespecified interfaceshow standby fastethernet 0/0Router#s1Displays HSRP group 1 informationfor the specified interfaceHSRP Optimization OptionsThere are options available that make it possible to optimize HSRP operation in the campusnetwork. The next three sections explain three of these options: standby preempt, messagetimers, and interface net 0/0Moves to interface configuration modestandby 1Router(config-if)#spreemptThis router will preempt, or take control of, theactive router if the local priority is higher thanthe active router

Hot Standby Routing Protocolstandby 1Router(config-if)#spreempt delay minimum 180Causes the local router to postpone taking overas the active router for 180 seconds since thatrouter was last restartedstandby 1Router(config-if)#spreempt delay reloadAllows for preemption to occur only after arouter reloadsno standbyRouter(config-if)#n1 preempt delay reloadDisables the preemption delay, but preemptionitself is still enabled. Use the no standby xpreempt command to eliminate preemption61NOTE: If the preempt argument is notconfigured, the local router assumes control asthe active router only if the local router receivesinformation indicating that there is no routercurrently in the active state.HSRP Message TimersinterfaceRouter(config)#ifastethernet 0/0Moves to interface config modestandby 1Router(config-if)#stimers 5 15Sets the hello timer to 5 seconds and sets thehold timer to 15 secondsNOTE: The hold timer is normally set to begreater than or equal to 3 times the hello timer.NOTE: The hello timer can be from 1 to 254;the default is 3. The hold timer can be from 1 to255; the default is 10. The default unit of time isseconds.standby 1Router(config-if)#stimers msec 200 msec 600Sets the hello timer to 200 milliseconds and setsthe hold timer to 600 millisecondsNOTE: If the msec argument is used, thetimers can be an integer from 15 to 999.

62Virtual Router Redundancy ProtocolInterface TrackinginterfaceRouter(config)#ifastethernet 0/0Moves to interface configuration modestandby 1Router(config-if)#strack serial 0/0 25HSRP will track the availability of interfaceserial 0/0. If serial 0/0 goes down, the priority ofthe router in group 1 will be decremented by 25.NOTE: The default value of the track argumentis 10.TIP: The track argument does not assign a newpriority if the tracked interface goes down. Thetrack argument assigns a value that the prioritywill be decreased if the tracked interface goesdown. Therefore, if you are tracking serial 0/0with a track value of 25—standby 1 track serial0/0 25—and serial 0/0 goes down, the prioritywill be decreased by 25; assuming a defaultpriority of 100, the new priority will now be 75.Debugging HSRPdebug standbyRouter#dDisplays all HSRP debugging information,including state changes and transmission/reception of HSRP packetsdebug standby errorsRouter#dDisplays HSRP error messagesdebug standby eventsRouter#dDisplays HSRP event messagesdebug standby eventsRouter#dterseDisplays all HSRP events except for hellos andadvertisementsdebug standby eventsRouter#dtrackDisplays all HSRP tracking eventsdebug standby packetsRouter#dDisplays HSRP packet messagesdebug standby terseRouter#dDisplays all HSRP errors, events, and packets,except for hellos and advertisementsVirtual Router Redundancy ProtocolNOTE: HSRP is Cisco proprietary. The Virtual Router Redundancy Protocol(VRRP) is an IEEE standard.

Virtual Router Redundancy Protocol63VRRP is an election protocol that dynamically assigns responsibility for one or more virtualrouters to the VRRP routers on a LAN, allowing several routers on a multiaccess link to usethe same virtual IP address. A VRRP router is configured to run VRRP in conjunction withone or more other routers attached.Configuring VRRPinterfaceRouter(config)#ifastethernet 0/0Moves to interface config modeipRouter(config-if)#iaddress 172.16.100.5255.255.255.0Assigns IP address and netmaskvrrp 10Router(config-if)#vip 172.16.100.1Enables VRRP for group 10 on this interface witha virtual address of 172.16.100.1.The group number can be from 1 to 255.vrrp 10Router(config-if)#vdescription EngineeringGroupAssigns a text description to the groupvrrp 10Router(config-if)#vpriority 110Sets the priority level for this router. The range isfrom 1 to 254. The default is 100.vrrp 10Router(config-if)#vpreemptThis router will preempt, or take over, as thevirtual router master for group 10 if it has a higherpriority than the current virtual router mastervrrp 10Router(config-if)#vpreempt delay minimum 60This router will preempt, but only after a delay of60 secondsNOTE: The default delay period is 0 seconds.vrrp 10Router(config-if)#vtimers advertise 15Configures the interval between successfuladvertisements by the virtual router masterNOTE: The default interval value is 1 second.NOTE: All routers in a VRRP group must use thesame timer values. If routers have different timervalues set, the VRRP group will not communicatewith each other.NOTE: The range of the advertisement timer is 1to 255 seconds. If you use the msec argument, youchange the timer to measure in milliseconds. Therange in milliseconds is 50 to 999.

64Virtual Router Redundancy Protocolvrrp 10Router(config-if)#vtimers learnConfigures the router, when acting as a virtualrouter backup, to learn the advertisement intervalused by the virtual router mastervrrp 10Router(config-if)#vshutdownDisables VRRP on the interface, but configurationis still retainedno vrrpRouter(config-if)#n10 shutdownReenables the VRRP group using the previousconfigurationVerifying VRRPshow running-configRouter#sDisplays contents of dynamic RAMshow vrrpRouter#sDisplays VRRP informationshow vrrp briefRouter#sDisplays a brief status of all VRRP groupsshow vrrp 10Router#sDisplays detailed information about VRRP group10show vrrp interfaceRouter#sfastethernet 0/0Displays information about VRRP as enabled oninterface fastethernet 0/0show vrrp interfaceRouter#sfastethernet 0/0 briefDisplays a brief summary about VRRP on interfacefastethernet 0/0Debugging VRRPdebug vrrp allRouter#dDisplays all VRRP messagesdebug vrrp errorRouter#dDisplays all VRRP error messagesdebug vrrp eventsRouter#dDisplays all VRRP event messagesdebug vrrp packetsRouter#dDisplays messages about packets sent and receiveddebug vrrp stateRouter#dDisplays messages about state transitions

Gateway Load Balancing Protocol65Gateway Load Balancing ProtocolGateway Load Balancing Protocol (GLBP) protects data traffic from a failed router orcircuit, like HSRP and VRRP, while allowing packet load sharing between a group ofredundant routers.Configuring GLBPinterface fastethernetRouter(config)#i0/0Moves to interface config modeip addressRouter(config-if)#i172.16.100.5 255.255.255.0Assigns IP address and netmaskglbp 10 ipRouter(config-if)#g172.16.100.1Enables GLBP for group 10 on thisinterface with a virtual address of172.16.100.1. The range of groupnumbers is from 0 to 1023.glbp 10 preemptRouter(config-if)#gConfigures the router to preempt, ortake over, as the active virtualgateway (AVG) for group 10 if thisrouter has a higher priority than thecurrent AVGglbp 10 preemptRouter(config-if)#gdelay minimum 60Configures the router to preempt, ortake over, as AVG for group 10 ifthis router has a higher priority thanthe current active virtual forwarder(AVF) after a delay of 60 secondsglbp 10 forwarderRouter(config-if)#gpreemptConfigures the router to preempt, ortake over, as AVF for group 10 if thisrouter has a higher priority than thecurrent AVF. This command isenabled by default with a delay of 30seconds.glbp 10 forwarderRouter(config-if)#gpreempt delay minimum 60Configures the router to preempt, ortake over, as AVF for group 10 if thisrouter has a higher priority than thecurrent AVF after a delay of 60seconds

66Gateway Load Balancing ProtocolNOTE: Members of a GLBP groupelect one gateway to be the AVG forthat group. Other group membersprovide backup for the AVG in theevent that the AVG becomesunavailable. The AVG assigns avirtual MAC address to eachmember of the GLBP group. Eachgateway assumes responsibility forforwarding packets sent to thevirtual MAC address assigned to itby the AVG. These gateways areknown as AVFs for their virtualMAC address.Virtual forwarder redundancy issimilar to virtual gatewayredundancy with an AVF. If the AVFfails, one of the secondary virtualforwarders in the listen stateassumes responsibility for the virtualMAC address.glbp 10 priority 150Router(config-if)#gSets the priority level of the routerNOTE: The range of the priorityargument is 1 to 255. The defaultpriority of GLBP is 100. A higherpriority number is preferred.glbp 10 timers 5 15Router(config-if)#gConfigures the hello timer to be setto 5 seconds and the hold timer to be15 secondsglbp 10 timers msecRouter(config-if)#g20200 msec 60600Configures the hello timer to be20,200 milliseconds and the holdtimer to be 60,600 milliseconds.NOTE: The default hello timer is 3seconds. The range of the hello timerinterval is 1 to 60 seconds. If themsec argument is used, the timerwill be measured in milliseconds,with a range of 50 to 60000.