© 2006 Cisco Systems, Inc. All rights reserved. BCMSN v Implementing Inter-VLAN Routing Deploying CEF-Based Multilayer Switching

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

© 2006 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.

© 2006 Cisco Systems, Inc. All rights reserved. BCMSN v CEF-Based Multilayer Switches CEF caches routing information in the FIB table and Layer 2 next-hop addresses in the adjacency table.

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

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

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

© 2006 Cisco Systems, Inc. All rights reserved. BCMSN v CEF-Based MLS Operation

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

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

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

© 2006 Cisco Systems, Inc. All rights reserved. BCMSN v Common CEF Problems Is ideal switching method (CEF, DCEF) in use? Are CEF tables complete and accurate?

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

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

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

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

© 2006 Cisco Systems, Inc. All rights reserved. BCMSN v How to Troubleshoot CEF

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

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