Layer 3 Switch Processing. CEF-Based Multilayer Switches. Layer 3 Switch Processing (Cont.)

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1 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 , Cisco Systems, Inc. All rights reserved. BCMSN v 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. 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 v , Cisco Systems, Inc. All rights reserved. BCMSN v

2 Multilayer Switch Packet Forwarding Process CEF-Based MLS Lookups 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. 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 v , Cisco Systems, Inc. All rights reserved. BCMSN v ARP Throttling CEF-Based MLS Operation 2003, Cisco Systems, Inc. All rights reserved. BCMSN v , Cisco Systems, Inc. All rights reserved. BCMSN v

3 Configuring and Verifying CEF Enabling 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 The commands required to enable CEF are platform dependent: On the Cisco Catalyst 4000 switch Switch(config-if)#ip cef On the Cisco Catalyst 3550 switch Switch(config-if)#ip route-cache cef 2003, Cisco Systems, Inc. All rights reserved. BCMSN v , Cisco Systems, Inc. All rights reserved. BCMSN v Verifying CEF Common CEF Problems Switch#show ip cef [type mod/port vlan_interface] [detail] Switch# show ip cef vlan 11 detail Is ideal switching method (CEF, DCEF) in use? Are CEF tables complete and accurate? 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 v , Cisco Systems, Inc. All rights reserved. BCMSN v

4 Verify Layer 3 Switching Displaying Hardware Layer 3 Switching Statistics Switch#show interface {{type mod/port} {port-channel number}} begin L3 Switch#show interfaces {{type mod/port} {port-channel number}} include switched 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# 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 v , Cisco Systems, Inc. All rights reserved. BCMSN v Adjacency Information Debugging CEF Operations 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 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 v , Cisco Systems, Inc. All rights reserved. BCMSN v

5 How to Troubleshoot CEF 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. BCMSN v , Cisco Systems, Inc. All rights reserved. BCMSN v Routing Issues: Using Default Gateways Configuring Layer 3 Redundancy with HSRP 2003, Cisco Systems, Inc. All rights reserved , Cisco Systems, Inc. All rights reserved. BCMSN v

6 Routing Issues: Using Proxy ARP Router Redundancy 2003, Cisco Systems, Inc. All rights reserved. BCMSN v , Cisco Systems, Inc. All rights reserved. BCMSN v Router Redundancy (Cont.) HSRP Standby group: The set of routers participating in HSRP that jointly emulate a virtual router 2003, Cisco Systems, Inc. All rights reserved. BCMSN v , Cisco Systems, Inc. All rights reserved. BCMSN v

7 The Active Router The Virtual Router MAC Address The active router responds to ARP requests with the MAC address of the virtual router. 2003, Cisco Systems, Inc. All rights reserved. BCMSN v , Cisco Systems, Inc. All rights reserved. BCMSN v The Standby Router Active and Standby Router Interaction The standby router listens for periodic hello messages on , Cisco Systems, Inc. All rights reserved. BCMSN v , Cisco Systems, Inc. All rights reserved. BCMSN v

8 HSRP States HSRP State Transition HSRP Standby Group 1 An HSRP router can be in one of six different states: Router A Priority 100 Router B Priority 50 Initial Initial Initial Learn Listen Speak Standby Active 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. Listen Speak Standby Active Listen Listen Speak Speak Standby Router B hears that router A has a higher priority, so router B returns to the listen state. 2003, Cisco Systems, Inc. All rights reserved. BCMSN v , Cisco Systems, Inc. All rights reserved. BCMSN v HSRP Standby State HSRP Active State A router in the standby state: Is a candidate for active router Sends hello messages Knows the virtual router IP address 2003, 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 2003, Cisco Systems, Inc. All rights reserved. BCMSN v

9 HSRP Configuration Commands Configuring an HSRP Standby Interface Configure standby 1 ip Verify show running-config show standby Enabling HSRP on a Cisco router interface automatically disables ICMP redirects. 2003, Cisco Systems, Inc. All rights reserved. BCMSN v , Cisco Systems, Inc. All rights reserved. BCMSN v Displaying the Standby Brief Status Summary Switch#show standby brief P indicates configured to preempt. Interface Grp Prio P State Active addr Standby addr Group addr Vl Active local 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. BCMSN v , Cisco Systems, Inc. All rights reserved. BCMSN v

10 HSRP Optimization Options Optimizing HSRP 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 , Cisco Systems, Inc. All rights reserved. BCMSN v Configuring HSRP Standby Priority Configuring HSRP Standby Preempt 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. Preempt enables a router to resume the forwarding router role. 2003, Cisco Systems, Inc. All rights reserved. BCMSN v , Cisco Systems, Inc. All rights reserved. BCMSN v

11 Configuring the Hello Message Timers HSRP Interface Tracking The holdtime parameter value should be at least three times the value of the hellotime parameter. 2003, Cisco Systems, Inc. All rights reserved. BCMSN v , Cisco Systems, Inc. All rights reserved. BCMSN v HSRP Interface Tracking (Cont.) 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 v , Cisco Systems, Inc. All rights reserved. BCMSN v

12 Tuning HSRP Multiple HSRP Groups 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. To load balance routers, assign them to multiple groups on the same subnet. 2003, Cisco Systems, Inc. All rights reserved. BCMSN v , Cisco Systems, Inc. All rights reserved. BCMSN v Addressing HSRP Groups Across Trunk Links About the HSRP Debug Command debug standby events debug standby terse 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 v , Cisco Systems, Inc. All rights reserved. BCMSN v

13 Debugging HSRP Summary 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 Example of HSRP debug showing standby group number mismatch 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. BCMSN v , Cisco Systems, Inc. All rights reserved. BCMSN v VRRP Configuring Layer 3 Redundancy with VRRP and GLBP 2003, Cisco Systems, Inc. All rights reserved , Cisco Systems, Inc. All rights reserved. BCMSN v

14 VRRP Operational Process Configuring VRRP on an Interface Enable VRRP on an interface and display the configuration. 2003, Cisco Systems, Inc. All rights reserved. BCMSN v , Cisco Systems, Inc. All rights reserved. BCMSN v 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 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 v , Cisco Systems, Inc. All rights reserved. BCMSN v

15 GLBP Operation GLBP Operation (Cont.) 2003, Cisco Systems, Inc. All rights reserved. BCMSN v , Cisco Systems, Inc. All rights reserved. BCMSN v GLBP Interface Tracking GLBP Interface Tracking (Cont.) 2003, Cisco Systems, Inc. All rights reserved. BCMSN v , Cisco Systems, Inc. All rights reserved. BCMSN v

16 Configuring GLBP on an Interface Summary Enable GLBP on an interface and display the configuration. 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. 2003, Cisco Systems, Inc. All rights reserved. BCMSN v , Cisco Systems, Inc. All rights reserved. BCMSN v