© 2006 Cisco Systems, Inc. All rights reserved. BCMSN v Implementing High Availability in a Campus Environment Configuring Layer 3 Redundancy with HSRP

© 2006 Cisco Systems, Inc. All rights reserved. BCMSN v Routing Issues: Using Default Gateways

© 2006 Cisco Systems, Inc. All rights reserved. BCMSN v Routing Issues: Using Proxy ARP

© 2006 Cisco Systems, Inc. All rights reserved. BCMSN v Router Redundancy

© 2006 Cisco Systems, Inc. All rights reserved. BCMSN v Router Redundancy (Cont.)

© 2006 Cisco Systems, Inc. All rights reserved. BCMSN v HSRP Standby group: The set of routers participating in HSRP that jointly emulate a virtual router

© 2006 Cisco Systems, Inc. All rights reserved. BCMSN v The active router responds to ARP requests with the MAC address of the virtual router. The Active Router

© 2006 Cisco Systems, Inc. All rights reserved. BCMSN v The Virtual Router MAC Address

© 2006 Cisco Systems, Inc. All rights reserved. BCMSN v The Standby Router The standby router listens for periodic hello messages on

© 2006 Cisco Systems, Inc. All rights reserved. BCMSN v Active and Standby Router Interaction

© 2006 Cisco Systems, Inc. All rights reserved. BCMSN v HSRP States An HSRP router can be in one of six different states: Initial Learn Listen Speak Standby Active

© 2006 Cisco Systems, Inc. All rights reserved. BCMSN v HSRP State Transition Initial Listen ActiveSpeak StandbyListen Speak Standby Router A Priority 100 Router B Priority 50 HSRP Standby Group 1 Router B hears that router A has a higher priority, so router B returns to the listen state. Router A does not hear any higher priority than itself, so promotes itself to standby. Router A does not hear an active router, so promotes itself to active.

© 2006 Cisco Systems, Inc. All rights reserved. BCMSN v A router in the standby state: Is a candidate for active router Sends hello messages Knows the virtual router IP address HSRP Standby State

© 2006 Cisco Systems, Inc. All rights reserved. BCMSN v A router in the active state: Assumes the active forwarding of packets for the virtual router Sends hello messages Knows the virtual router IP address HSRP Active State

© 2006 Cisco Systems, Inc. All rights reserved. BCMSN v HSRP Configuration Commands Configure standby 1 ip Verify show running-config show standby

© 2006 Cisco Systems, Inc. All rights reserved. BCMSN v Enabling HSRP on a Cisco router interface automatically disables ICMP redirects. Configuring an HSRP Standby Interface

© 2006 Cisco Systems, Inc. All rights reserved. BCMSN v Displaying the Standby Brief Status Switch#show standby brief P indicates configured to preempt. | Interface Grp Prio P State Active addr Standby addr Group addr Vl Active local

© 2006 Cisco Systems, Inc. All rights reserved. BCMSN v Summary Router redundancy allows two or more routers to work as a group to maintain forwarding of IP packets. A single default gateway or proxy ARP does not provide the redundancy required in a campus network. HSRP provides router redundancy to end devices. HSRP operates to provide nonstop path redundancy for IP. An HSRP-enabled router will exist in a specific state or transition through a series of states. HSRP is configured using the standby command. HSRP is enabled per interface.

© 2006 Cisco Systems, Inc. All rights reserved. BCMSN v