1. © 2009 Cisco Systems, Inc. All rights reserved. SWITCH v1.0—6-1 Implementing Layer 3 High Availability Configuring Layer 3 Redundancy with HSRP

2. © 2009 Cisco Systems, Inc. All rights reserved. SWITCH v1.0—6-2 Routing Issues: Using Proxy ARP

3. © 2009 Cisco Systems, Inc. All rights reserved. SWITCH v1.0—6-3 Routing Issues: Using Default Gateways

4. © 2009 Cisco Systems, Inc. All rights reserved. SWITCH v1.0—6-4 Router Redundancy

5. © 2009 Cisco Systems, Inc. All rights reserved. SWITCH v1.0—6-5 Router Redundancy Failover

6. © 2009 Cisco Systems, Inc. All rights reserved. SWITCH v1.0—6-6 HSRP Configuration Standby group  Set of HSRP devices emulating a virtual router Enabling HSRP on an interface automatically disables ICMP redirects.

7. © 2009 Cisco Systems, Inc. All rights reserved. SWITCH v1.0—6-7 Virtual Router MAC Address

8. © 2009 Cisco Systems, Inc. All rights reserved. SWITCH v1.0—6-8 Forwarding Through Active Router

9. © 2009 Cisco Systems, Inc. All rights reserved. SWITCH v1.0—6-9 Active and Standby Routers Active router  Responds to ARP requests of the default gateway with the MAC address of the virtual router  Assumes the active forwarding of packets for the virtual router  Sends hello messages  Knows the virtual router IP address Standby router  Listens for periodic hello messages  Assumes the active forwarding of packets if no messages heard from active router

10. © 2009 Cisco Systems, Inc. All rights reserved. SWITCH v1.0—6-10 HSRP States An HSRP router can be in one of five states. StateDefinition Initial The state at the start. State after configuration change or when an interface first comes up. Listen The router knows the virtual IP address. It listens for hello messages from other routers. Speak The router sends periodic hello messages and actively participates in the election of the active or standby router. Standby The router is a candidate to become the next active router and sends periodic hello messages. Active The router currently forwards packets that are sent to the group virtual MAC address. The router sends periodic hello messages.

11. © 2009 Cisco Systems, Inc. All rights reserved. SWITCH v1.0—6-11 HSRP State Transition

12. © 2009 Cisco Systems, Inc. All rights reserved. SWITCH v1.0—6-12 HSRP Priority and Preemption  The device with the highest priority in an HSRP group becomes the active router.  The default priority is 100.  In the case of a tie, the router with the highest configured IP address will become active.  Preemption enables the higher priority device to become active. switch(config)# interface vlan 10 switch(config-if)# ip address 10.1.1.2 255.255.255.0 switch(config-if)# standby 10 ip 10.1.1.1 switch(config-if)# standby 10 priority 110 switch(config-if)# standby 10 preempt

13. © 2009 Cisco Systems, Inc. All rights reserved. SWITCH v1.0—6-13 HSRP and STP Configured active router should be the same as STP root bridge. Blocked uplink caused traffic to take less-than- optimal path.

14. © 2009 Cisco Systems, Inc. All rights reserved. SWITCH v1.0—6-14 HSRP Authentication  Configure authentication string (maximum of eight characters, default cisco) for standby group. switch(config)# interface vlan 10 switch(config-if)# ip address 10.1.1.2 255.255.255.0 switch(config-if)# standby 10 ip 10.1.1.1 switch(config-if)# standby 10 priority 110 switch(config-if)# standby 10 preempt switch(config-if)# standby 10 authentication xyz123

15. © 2009 Cisco Systems, Inc. All rights reserved. SWITCH v1.0—6-15 HSRP and Timers When active HSRP fails, timers can determine how fast standby should become active. Failover delay configuration should also take into account IGP convergence delay.

16. © 2009 Cisco Systems, Inc. All rights reserved. SWITCH v1.0—6-16 HSRP Timer Configuration  Configure hello time and hold time to millisecond values.  The hold time parameter value should be at least three times the value of the hello time parameter.  Configure the preempt delay timer so that preemption occurs after the switch has fully rebooted and has established full connectivity to the network. switch(config)# interface vlan 10 switch(config-if)# ip address 10.1.1.2 255.255.255.0 switch(config-if)# standby 10 ip 10.1.1.1 switch(config-if)# standby 10 priority 110 switch(config-if)# standby 10 preempt switch(config-if)# standby 10 timers msec 200 msec 750 switch(config-if)# standby 10 preempt delay minimum 300

17. © 2009 Cisco Systems, Inc. All rights reserved. SWITCH v1.0—6-17 HSRP Versions HSRPv1 (default).  Group number from 0 to 255.  Virtual MAC address 0000.0C07.ACXX (XX = HSRP group).  Hello packets sent to multicast address 224.0.0.2. HSRPv2 (Cisco IOS Release 12.2(46)SE and later).  Group number from 0 to 4095.  Virtual MAC address 0000.0C9F.FXXX (XXX = HSRP group).  Hello packets sent to multicast address 224.0.0.102.  HSRPv2 and HSRPv1 have different packet formats. Configure same version on all devices of HSRP group. switch(config-if)# standby 10 version 2

18. © 2009 Cisco Systems, Inc. All rights reserved. SWITCH v1.0—6-18 Displaying the Standby Status switch# show standby Vlan10 - Group 10 State is Active 1 state change, last state change 00:00:43 Virtual IP address is 10.1.10.1 Active virtual MAC address is 0000.0c07.ac0a Local virtual MAC address is 0000.0c07.ac0a (v1 default) Hello time 3 sec, hold time 10 sec Next hello sent in 0.016 secs Preemption enabled Active router is local Standby router is 10.1.10.3, priority 90 (expires in 11.328 sec) Priority 110 (configured 110) Group name is "hsrp-Vl10-10" (default) switch# show standby brief P indicates configured to preempt. | Interface Grp Pri P State Active Standby Virtual IP Vl10 10 110 P Active local 10.1.10.3 10.1.10.1

19. © 2009 Cisco Systems, Inc. All rights reserved. SWITCH v1.0—6-19 HSRP Interface Tracking

20. © 2009 Cisco Systems, Inc. All rights reserved. SWITCH v1.0—6-20 HSRP Interface Tracking  Configure the standby group.  Configure priority (default is 100).  Configure preempt on all devices within the HSRP group.  Configure the tracked interfaces and decrement (default decrement is 10). switch(config)# interface vlan 10 switch(config-if)# ip address 10.1.1.2 255.255.255.0 switch(config-if)# standby 10 ip 10.1.1.1 switch(config-if)# standby 10 priority 110 switch(config-if)# standby 10 preempt switch(config-if)# standby 10 track fastethernet0/23 20 switch(config-if)# standby 10 track fastethernet0/24

21. © 2009 Cisco Systems, Inc. All rights reserved. SWITCH v1.0—6-21 Tracking Options Standby command can track interface or object. Tracked objects are defined with track object_number.  Track number interface can verify line protocol or IP routing capability.  Track number ip route can verify network reachability.  Track number list can define complex conditions.  Track number rtr can verify parameters such as IP SLA. switch(config)# track 1 ? interface Select an interface to track ip IP protocol list Group objects in a list rtr Response Time Reporter (RTR) entry

22. © 2009 Cisco Systems, Inc. All rights reserved. SWITCH v1.0—6-22 HSRP and IP SLA Tracking

23. © 2009 Cisco Systems, Inc. All rights reserved. SWITCH v1.0—6-23 Multiple HSRP Groups  To load-balance links between access and distribution, configure the HSRP active router and the spanning-tree root for each VLAN to be on the same multilayer switch.

24. © 2009 Cisco Systems, Inc. All rights reserved. SWITCH v1.0—6-24 Multiple HSRP Group Configuration

25. © 2009 Cisco Systems, Inc. All rights reserved. SWITCH v1.0—6-25 Monitoring HSRP SW1#show standby brief P indicates configured to preempt. | Interface Grp Pri P State Active Standby Virtual IP Vl63 63 120 P Active local 10.1.63.2 10.1.63.254 Vl64 64 90 P Standby 10.1.64.1 local 10.1.64.254 SW1#show standby neighbor vlan64 HSRP neighbors on Vlan64 10.1.64.1 Active groups: 64 No standby groups

26. © 2009 Cisco Systems, Inc. All rights reserved. SWITCH v1.0—6-26 Summary  A single default gateway or proxy ARP does not provide the redundancy that is required in a campus network.  HSRP provides router redundancy to end devices.  HSRP is configured using the standby command for each interface.  Preemption, timers, and interface tracking are options that can be configured to optimize HSRP and reduce failover time.  Specific debug commands are used to view the HSRP state changes.

27. © 2009 Cisco Systems, Inc. All rights reserved. SWITCH v1.0—6-27