Bcmsn30s04 Intervlan Routing

7/27/2019 Bcmsn30s04 Intervlan Routing

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Implementing Inter-VLAN Routing

Describing Routing Between VLANs



Inter-VLAN Routing with External Router

• Single trunk link carries traffic for multiple VLANs to and

from router.



Inter-VLAN RoutingExternal Router Configuration Commands

Configure on subinterface

• encapsulation dot1Q (or isl) 10

• ip address 10.10.1.1 255.255.255.0

Verify• show vlan 10

• show ip route



Inter-VLAN Routing on External Router:802.1Q Trunk Link



Inter-VLAN Routing on External Router:ISL Trunk Link



Verifying Inter-VLAN Routing

The ping command tests connectivity to remote hosts.



Verifying the Inter-VLAN RoutingConfiguration

Router#show ip interface brief

• Displays the current IP configuration per VLAN

Router#show ip route

• Displays IP route table information

Router#show vlan

• Displays IP address on interfaces and current state of interface



Explaining Multilayer Switching



Layer 2 Switch Forwarding Process



Logical Packet Flow for aMultilayer Switch



Rewritten IP Unicast Packet

IP Unicast Frame and Packet Rewrite

Incoming IP Unicast Packet



CAM Table

• Requires an exactmatch on all bits

• Matching is a binary

operation: 0 or 1

• Provides very high-speed lookups



TCAM Table

• Matches only significantvalues

• Matches based on threevalues: 0, 1, or X (either)

•Masks used to wildcard somecontent fields



Summary

• A router on a stick can be used to route between VLANsusing either ISL or 802.1Q as the trunking protocol.

• A router on a stick requires subinterfaces, one for each VLAN.

•Verify inter-VLAN routing by generating IP packets betweentwo subnets.

• Multilayer switches can forward traffic at both Layer 2 andLayer 3.

• Multilayer switches rewrite the Layer 2 and Layer 3 header

using tables held in hardware.




Enabling Routing Between VLANs on aMultilayer Switch



Layer 3 SVI



SVI on a Multilayer Switch

Configure

• ip routing

• interface vlan 10

– ip address 10.1.1.1 255.255.255.0

• router eigrp 50

– network 10.0.0.0

Verify

•

show ip route



Configuring Inter-VLAN RoutingThrough an SVI

Switch(config)#ip routing

Step 1 : Configure IP routing.

Switch(config)#router ip_routing_protocol <options>

Step 4 : Configure the IP routing protocol if needed.

Switch(config)#interface vlan vlan-id

Step 2 : Create an SVI interface.

Switch(config-if)#ip address ip-address mask

Step 3 : Assign an IP address to the SVI.



Routed Ports on a Multilayer Switch (Cont.)



Routed Ports on a Multilayer Switch

• Physical switch port with Layer 3 capability

• Not associated with a VLAN

• Requires removal of Layer 2 port functionality

Configure

• ip routing

• interface fa0/1

– no switchport

– ip address 10.3.3.1 255.255.255.0

• router eigrp 50

– network 10.0.0.0



Configuring a Routed Port

Switch(config)#ip routing

Step 1 : Configure IP routing.

Switch(config)#router ip_routing_protocol <options>

Step 4 : Configure the IP routing protocol if needed.

Switch(config-if)#no switchport

Step 2 : Create a routed port.

Switch(config-if)#ip address ip-address mask

Step 3 : Assign an IP address to the routed port.



Summary

• SVI is a VLAN of switch ports represented by one interface tothe routing system.

• Specific commands are used to configure and verify routingon multilayer switch interfaces.

•The interface vlan command creates the SVI.

• A routed port has Layer 3 attributes.

• A routed port requires the removal of Layer 2 portfunctionality with the no switchport command.

• To receive dynamic updates, a routing protocol is required.




Deploying CEF-Based Multilayer Switching



Layer 3 Switch Processing

In Layer 3 switches, thecontrol path and data pathare relatively independent.

• The control path code,such as routing

protocols, runs on theroute processor.

• Data packets areforwarded by theswitching fabric.



Layer 3 Switch Processing (Cont.)

Layer 3 switching can occur at two different locationson the switch.

• Centralized switching: Switching decisions are made on theroute processor by a central forwarding table.

• Distributed switching: Switching decisions can be made on aport or line-card level.

Layer 3 switching takes place using one of these twomethods:

•Route caching: A Layer 3 route cache is built in hardware asthe switch sees traffic flow into the switch.

• Topology-based switching: Information from the routingtable is used to populate the route cache, regardlessof traffic.



CEF-Based Multilayer Switches

• CEF caches routing information in the FIB tableand Layer 2 next-hop addresses in the adjacencytable.



Multilayer Switch Packet Forwarding Process

• Some IP packets cannot beprocessed in hardware.

• If an IP packet cannot beprocessed in hardware, it isprocessed by the Layer 3engine.



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.



ARP Throttling



CEF-Based MLS Operation



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



Enabling CEF

Switch(config-if)#ip cef

Switch(config-if)#ip route-cache cef

The commands required to enable CEF are platformdependent:

• On the Cisco Catalyst 4000 switch

• On the Cisco Catalyst 3550 switch



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, 14248 bytes, 14 inserts, 1 invalidations0 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)

172.16.11.0/24, version 6, epoch 0, attached, connected

0 packets, 0 bytes

via Vlan11, 0 dependencies

valid glean adjacency



Common CEF Problems

• Is ideal switching method (CEF, DCEF) in use?

• Are CEF tables complete and accurate?



Di l i H d L 3 S it hi



Displaying Hardware Layer 3 SwitchingStatistics

Switch#show interfaces {{type mod/port} | {port-channelnumber }} include switched

Switch#show interfaces gigabitethernet 9/5 | include switched

L2 Switched: ucast: 8199 pkt, 1362060 bytes - mcast: 6980 pkt, 371952 bytes

L3 in Switched: ucast: 3045 pkt, 742761 bytes - mcast: 0 pkt, 0 bytes mcast

L3 out Switched: ucast: 2975 pkt, 693411 bytes - mcast: 0 pkt, 0 bytes



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 GigabitEthernet9/5 172.20.53.206(11)

504 packets, 6110 bytes

00605C865B82

000164F83FA50800

ARP 03:49:31



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



How to Troubleshoot CEF



Summary

• Layer 3 switching is high-performance packet switchingin hardware.

• MLS functionality can be implemented through CEF.

• CEF uses tables in hardware to forward packets.

• Specific commands are used to enable and verifyCEF operations.

• Commands to enable CEF are platform dependent.

• CEF problems can be matched to specific solutions.

•

Specific commands are used to troubleshoot and solveCEF problems.

• Ordered steps assist in troubleshooting CEF-basedproblems.



Module Summary

• An external router can be configured to route packetsbetween the VLANs on a Layer 2 switch.

• Multilayer switches allow routing and the configuration of interfaces to pass packets between VLANs.

•

CEF-based multilayer switching facilitates packet switchingin hardware.



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Bcmsn30s04 Intervlan Routing

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