© 2003, Cisco Systems, Inc. All rights reserved. 2-1 Deploying CEF-Based Multilayer Switching

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-2 Layer 3 Switch Processing In Layer 3 switches, the control path and data path are relatively independent. The control path code, such as routing protocols, runs on the route processor. Data packets are forwarded by the switching fabric.

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-3 Layer 3 Switch Processing (Cont.) Layer 3 switching can occur at two different locations on the switch. Centralized switching: Switching decisions are made on the route processor by a central forwarding table. Distributed switching: Switching decisions can be made on a port or line-card level. Layer 3 switching takes place using one of these two methods: Route caching: A Layer 3 route cache is built in hardware as the switch sees traffic flow into the switch. Topology-based switching: Information from the routing table is used to populate the route cache, regardless of traffic.

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-4 CEF-Based Multilayer Switches CEF caches routing information in the FIB table and Layer 2 next-hop addresses in the adjacency table.

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-5 Multilayer Switch Packet Forwarding Process Some IP packets cannot be processed in hardware. If an IP packet cannot be processed in hardware, it is processed by the Layer 3 engine.

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-6 CEF-Based MLS Lookups 1. Layer 3 packets initiate TCAM lookup. 2. The longest match returns adjacency with rewrite information. 3. The packet is rewritten per adjacency information and forwarded.

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-7 ARP Throttling

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-8 CEF-Based MLS Operation

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-9 Configuring and Verifying CEF Configuring CEF ip cef (enabled by default) ip route-cache cef (only on VLAN interface) Verifying CEF show ip cef fa 0/1 detail show adjacency fa 0/1 detail

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-10 Enabling CEF Switch(config-if)#ip cef Switch(config-if)#ip route-cache cef The commands required to enable CEF are platform dependent: On the Cisco Catalyst 4000 switch On the Cisco Catalyst 3550 switch

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-11 Verifying CEF Switch#show ip cef [type mod/port | vlan_interface] [detail] Switch# show ip cef vlan 11 detail IP CEF with switching (Table Version 11), flags=0x0 10 routes, 0 reresolve, 0 unresolved (0 old, 0 new), peak 0 13 leaves, 12 nodes, bytes, 14 inserts, 1 invalidations 0 load sharing elements, 0 bytes, 0 references universal per-destination load sharing algorithm, id 4B936A24 2(0) CEF resets, 0 revisions of existing leaves Resolution Timer: Exponential (currently 1s, peak 1s) 0 in-place/0 aborted modifications refcounts: 1061 leaf, 1052 node Table epoch: 0 (13 entries at this epoch) /24, version 6, epoch 0, attached, connected 0 packets, 0 bytes via Vlan11, 0 dependencies valid glean adjacency

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-12 Common CEF Problems Is ideal switching method (CEF, DCEF) in use? Are CEF tables complete and accurate?

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-13 Verify Layer 3 Switching Switch#show interface {{type mod/port} | {port-channel number}} | begin L3 Switch#show interface fastethernet 3/3 | begin L3 L3 in Switched: ucast: 0 pkt, 0 bytes - mcast: 12 pkt, 778 bytes mcast L3 out Switched: ucast: 0 pkt, 0 bytes - mcast: 0 pkt, 0 bytes packets input, bytes, 0 no buffer Received broadcasts, 2 runts, 0 giants, 0 throttles..... Switch#

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-14 Displaying Hardware Layer 3 Switching Statistics Switch#show interfaces {{type mod/port} | {port-channel number}} include switched Switch#show interfaces gigabitethernet 9/5 | include switched L2 Switched: ucast: 8199 pkt, bytes - mcast: 6980 pkt, bytes L3 in Switched: ucast: 3045 pkt, bytes - mcast: 0 pkt, 0 bytes mcast L3 out Switched: ucast: 2975 pkt, bytes - mcast: 0 pkt, 0 bytes

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-15 Adjacency Information Switch#show adjacency [{{type mod/port} | {port-channel number}} | detail | internal | summary] Switch#show adjacency gigabitethernet 9/5 detail Protocol Interface Address IP GigabitEthernet9/ (11) 504 packets, 6110 bytes 00605C865B F83FA50800 ARP 03:49:31

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-16 Debugging CEF Operations Switch#debug ip cef {drops | access-list | receive | events | prefix-ipc | table} Displays debug information for CEF Switch#debug ip cef {ipc | interface-ipc} Displays debug information related to IPC in CEF Switch#ping ip Performs an extended ping

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-17 How to Troubleshoot CEF

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-18 Summary Layer 3 switching is high-performance packet switching in hardware. MLS functionality can be implemented through CEF. CEF uses tables in hardware to forward packets. Specific commands are used to enable and verify CEF operations. Commands to enable CEF are platform dependent. CEF problems can be matched to specific solutions. Specific commands are used to troubleshoot and solve CEF problems. Ordered steps assist in troubleshooting CEF-based problems.

© 2003, Cisco Systems, Inc. All rights reserved Implementing High Availability in a Campus Environment Configuring Layer 3 Redundancy with HSRP

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-20 Routing Issues: Using Default Gateways

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-21 Routing Issues: Using Proxy ARP

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-22 Router Redundancy

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-23 Router Redundancy (Cont.)

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-24 HSRP Standby group: The set of routers participating in HSRP that jointly emulate a virtual router

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-25 The active router responds to ARP requests with the MAC address of the virtual router. The Active Router

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-26 The Virtual Router MAC Address

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-27 The Standby Router The standby router listens for periodic hello messages on

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-28 Active and Standby Router Interaction

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-29 HSRP States An HSRP router can be in one of six different states: Initial Learn Listen Speak Standby Active

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-30 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.

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-31 A router in the standby state: Is a candidate for active router Sends hello messages Knows the virtual router IP address HSRP Standby State

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-32 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

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-33 HSRP Configuration Commands Configure standby 1 ip Verify show running-config show standby

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-34 Enabling HSRP on a Cisco router interface automatically disables ICMP redirects. Configuring an HSRP Standby Interface

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-35 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

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-36 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.

© 2003, Cisco Systems, Inc. All rights reserved Implementing High Availability in a Campus Environment Optimizing HSRP

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-38 HSRP Optimization Options These options can be configured to optimize HSRP: HSRP standby priority HSRP standby preempt Hello message timers HSRP interface tracking

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-39 Configuring HSRP Standby Priority The router 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.

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-40 Configuring HSRP Standby Preempt Preempt enables a router to resume the forwarding router role.

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-41 Configuring the Hello Message Timers The holdtime parameter value should be at least three times the value of the hellotime parameter.

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-42 HSRP Interface Tracking

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-43 HSRP Interface Tracking (Cont.)

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-44 Configuring HSRP Tracking Switch(config-if)#standby [group-number] track type number [interface-priority] Configures HSRP tracking Switch(config)#interface vlan 10 Switch(config-if)#standby 1 track GigabitEthernet 0/7 50 Switch(config-if)#standby 1 track GigabitEthernet 0/8 60 Example of HSRP tracking Note: Preempt must be configured on all participating devices within the HSRP group.

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-45 Tuning HSRP Configure hellotime and holdtime to millisecond values. Configure preempt delay timer so that preempt occurs only after the distribution switch has fully rebooted and established full connectivity to the rest of the network.

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-46 To load balance routers, assign them to multiple groups on the same subnet. Multiple HSRP Groups

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-47 Addressing HSRP Groups Across Trunk Links To load balance routers and links: –Per VLAN, configure the HSRP active router and the spanning tree root to be the same multilayer switch.

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-48 About the HSRP Debug Command debug standby events debug standby terse

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-49 Debugging HSRP Example of HSRP debug showing standby group number mismatch DSW111#debug standby *Mar 4 19:08:08.918: HSRP: Vl1 Grp 1 Hello out Active pri 150 vIP *Mar 4 19:08:09.287: HSRP: Vl1 Grp 2 Hello in Active pri 50 vIP *Mar 4 19:08:09.287: HSRP: Vl1 API active virtual address found *Mar 4 19:08:09.891: HSRP: Vl1 API Duplicate ARP entry detected for *Mar 4 19:08:09.891: HSRP: Vl1 Grp 1 Hello out Active pri 150 vIP *Mar 4 19:08:10.294: HSRP: Vl1 Grp 2 Hello in Active pri 50 vIP *Mar 4 19:08:10.294: HSRP: Vl1 API active virtual address found *Mar 4 19:08:10.294: HSRP: Vl1 API Duplicate ARP entry detected for *Mar 4 19:08:10.294: HSRP: Vl1 Grp 1 Hello out Active pri 150 vIP *Mar 4 19:08:10.294: HSRP: Vl1 Grp 2 Hello in Active pri 50 vIP *Mar 4 19:08:10.294: HSRP: Vl1 API active virtual address found *Mar 4 19:08:10.898: HSRP: Vl1 API Duplicate ARP entry detected for *Mar 4 19:08:10.898: HSRP: Vl1 Grp 1 Hello out Active pri 150 vIP *Mar 4 19:08:10.965: HSRP: Vl1 Grp 2 Hello in Active pri 50 vIP *Mar 4 19:08:11.300: HSRP: Vl1 API active virtual address found

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-50 Summary Preempt, timers, and interface tracking are options that can be configured to optimize HSRP. HSRP preempt can be tuned by adjusting timers that can thereby reduce failover time. To facilitate load sharing, a single interface on a router can be a member of multiple HSRP groups. Specific debug commands are used to view HSRP state changes. Debug can be used to discover the virtual IP address and the priority of the active and standby routers.

© 2003, Cisco Systems, Inc. All rights reserved Implementing High Availability in a Campus Environment Configuring Layer 3 Redundancy with VRRP and GLBP

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-52 VRRP

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-53 VRRP Operational Process

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-54 Configuring VRRP on an Interface Enable VRRP on an interface and display the configuration.

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-55 Gateway Load Balancing Protocol Single virtual IP address and multiple virtual MAC addresses Traffic to single gateway distributed across routers Automatic rerouting in the event of any failure Full use of resources on all routers without the administrative burden of creating multiple groups

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-56 GLBP Operations GLBP group members elect one AVG. AVG assigns a virtual MAC address to each member of the group. AVG replies to the ARP requests from clients with different virtual MAC addresses, thus achieving load balancing. Each router becomes an AVF for frames that are addressed to that virtual MAC address.

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-57 GLBP Operation

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-58 GLBP Operation (Cont.)

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-59 GLBP Interface Tracking

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-60 GLBP Interface Tracking (Cont.)

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-61 Configuring GLBP on an Interface Enable GLBP on an interface and display the configuration.

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-62 Summary VRRP provides router redundancy in a manner similar to HSRP. VRRP supports a master and one or more backup routers. VRRP and GLBP are configured per interface. GLBP provides router redundancy and load balancing. GLBP balances traffic by allocating a virtual MAC address to each AVF.