bcmsn30s04 intervlan routing
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Implementing Inter-VLAN Routing
Describing Routing Between VLANs
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Inter-VLAN Routing with External Router
• Single trunk link carries traffic for multiple VLANs to and
from router.
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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
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Inter-VLAN Routing on External Router:802.1Q Trunk Link
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Inter-VLAN Routing on External Router:ISL Trunk Link
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Verifying Inter-VLAN Routing
The ping command tests connectivity to remote hosts.
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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
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Explaining Multilayer Switching
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Layer 2 Switch Forwarding Process
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Logical Packet Flow for aMultilayer Switch
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Rewritten IP Unicast Packet
IP Unicast Frame and Packet Rewrite
Incoming IP Unicast Packet
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CAM Table
• Requires an exactmatch on all bits
• Matching is a binary
operation: 0 or 1
• Provides very high-speed lookups
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TCAM Table
• Matches only significantvalues
• Matches based on threevalues: 0, 1, or X (either)
•Masks used to wildcard somecontent fields
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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.
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Implementing Inter-VLAN Routing
Enabling Routing Between VLANs on aMultilayer Switch
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Layer 3 SVI
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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
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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.
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Routed Ports on a Multilayer Switch (Cont.)
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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
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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.
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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.
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Implementing Inter-VLAN Routing
Deploying CEF-Based Multilayer Switching
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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.
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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.
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CEF-Based Multilayer Switches
• CEF caches routing information in the FIB tableand Layer 2 next-hop addresses in the adjacencytable.
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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.
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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.
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ARP Throttling
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CEF-Based MLS Operation
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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
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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
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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
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Common CEF Problems
• Is ideal switching method (CEF, DCEF) in use?
• Are CEF tables complete and accurate?
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Di l i H d L 3 S it hi
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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
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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
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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
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How to Troubleshoot CEF
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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.
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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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