Section 5-6. Routing Tables


5-6. Routing Tables

  • To move packets between separate networks, the switching processor must have knowledge of the destination network.

  • Networks that are connected to a physical or virtual interface are connected routes and are automatically known by the switching processor.

  • You can configure the Layer 3 switching processor with statically defined routes by entering the routes into the configuration file.

  • One of the most common ways to learn and maintain routes is to use a dynamic routing protocol, such as Open Shortest Path First (OSPF) Protocol or Enhanced Interior Gateway Routing Protocol (EIGRP).

Configuration

1.

Access the Layer 3 switching processor.

If the switching processor is a card that runs as a subsystem in a COS device, you need to access this device to perform any configuration. To access the device, use the session command. This command is not required for a switch running Supervisor IOS because you are communicating directly with the Layer 3 switch processor:

COS

 (privileged)session mod 


The mod number specifies the module number of the switch processor. Use the command show modules to locate this processor if you do not know where it is located in the switch.

2.

Establish connected routes:

IOS

 (interface) ip address address mask 


By specifying a network address on an interface, you have also established an entry for that network in the routing table. This step shows the configuration for an IP address, but the same would hold true for other protocols (as shown in the section "5-2: Layer 3 Ethernet Interfaces").

3.

Establish static routes:

IOS

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 (global) ip route network netmask {nexthop |  interface} [admin-distance] 


This command specifies a static route for the network using the mask specified. The nexthop address or interface shows how to get to the network configured.

4.

Enable dynamic routes:

IOS

 (global) router protocol (router)network network 


The router command along with a protocol such as Routing Information Protocol (RIP), OSPF, or EIGRP places you in router configuration mode. In this mode, you specify the networks for which you want to run the protocol.

NOTE

This section is an abbreviated look at establishing and maintaining routes. It is intended as a reminder and not as a comprehensive configuration of routing protocols. A Layer 3 switch works exactly like a router for maintaining routes. Refer to Cisco Field Manual: Router Configuration by Cisco Press for more detailed configuration information. For more general information on routing and routing technologies, see the "Further Reading" section at the end of the chapter.


Verifying Routes

After you have configured a port for trunking, use one of the following commands to verify the VLAN port assignments:

IOS

 (privileged) show protocol route 


The protocol option enables you to look at the routing table for a given protocol, such as IP, IPX, or AppleTalk.



Cisco Field Manual. Catalyst Switch Configuration
Cisco Field Manual. Catalyst Switch Configuration
ISBN: 1587050439
EAN: N/A
Year: 2001
Pages: 150

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