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This chapter describes how to configure Layer 3 interfaces on the Catalyst 6000 family switches.
This chapter consists of these sections:
Network devices in different VLANs cannot communicate with one another without a router to route traffic between the VLANs. In most network environments, VLANs are associated with individual networks or subnetworks.
For example, in an IP network, each subnetwork is mapped to an individual VLAN. In a Novell IPX network, each VLAN is mapped to an IPX network number. In an AppleTalk network, each VLAN is associated with a cable range and AppleTalk zone name.
Configuring VLANs helps control the size of the broadcast domain and keeps local traffic local. However, when an end station in one VLAN needs to communicate with an end station in another VLAN, interVLAN communication is required. This communication is supported by interVLAN routing. You configure one or more routers to route traffic to the appropriate destination VLAN.
Figure 8-1 shows a basic routing topology. Switch A is in VLAN 10 and Switch B is in VLAN 20. The router has an interface in each VLAN.
When Host A in VLAN 10 needs to communicate with Host B in VLAN 10, it sends a packet addressed to that host. Switch A forwards the packet directly to Host B, without sending it to the router.
When Host A sends a packet to Host C in VLAN 20, Switch A forwards the packet to the router, which receives the traffic on the VLAN 10 interface. The router checks the routing table, determines the correct outgoing interface, and forwards the packet out the VLAN 20 interface to Switch B. Switch B receives the packet and forwards it to Host C.
IP routing is automatically enabled in the Cisco IOS software. For detailed IP routing configuration information, refer to the IOS Network Protocols Configuration Guide, Part 1.
These sections describe how to configure routing on the Catalyst 6000 family switch:
Configuring routing consists of two main procedures:
1. To support VLAN interfaces, create and configure VLANs on the switch and assign VLAN membership to Layer 2 interfaces. For more information, see "Configuring VLANs" and "Configuring VTP."
2. Configure Layer 3 interfaces, either VLAN interfaces or physical Layer 3 interfaces. Configure a VLAN interface for each VLAN for which you want to route traffic. VLAN interfaces are virtual interfaces that you configure in the same way as physical Layer 3 interfaces.
To configure an IP address on a Layer 3 interface, perform this task:
| Step | Command | Purpose | ||
|---|---|---|---|---|
| Router(config)# interface {vlan vlan_ID} | {{ethernet | fastethernet | gigabitethernet} slot/port} | {port-channel port_channel_number}
| Select an interface to configure. | ||
| Router(config-if)# ip address ip_address subnet_mask | Configure the IP address and IP subnet. | ||
| Router(config-if)# no shutdown | Enable the interface. | ||
| Router(config-if)# end | Exit configuration mode. | ||
| Router# copy running-config startup-config | Save your configuration changes to NVRAM. | ||
| Router# show interfaces [type slot/interface] Router# show ip interfaces [type slot/interface] Router# show running-config interfaces [type slot/interface] | Verify the configuration. |
This example shows how to configure an IP address on Fast Ethernet interface 5/4:
Router# configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router(config)# interface fastethernet 5/4 Router(config-if)# ip address 172.20.52.106 255.255.255.248 Router(config-if)# no shutdown Router(config-if)# Router(config-if)# end Router#
This example uses the show interfaces command to display the interface IP address configuration and status of Fast Ethernet interface 5/4:
Router# show interfaces fastethernet 5/4
FastEthernet5/4 is up, line protocol is up
Hardware is Cat6K 100Mb Ethernet, address is 0050.f0ac.3058 (bia 0050.f0ac.3058)
Internet address is 172.20.52.106/29
MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
Full-duplex, 100Mb/s
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:01, output never, output hang never
Last clearing of "show interface" counters never
Queueing strategy: fifo
Output queue 0/40, 0 drops; input queue 0/75, 0 drops
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
7 packets input, 871 bytes, 0 no buffer
Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 input packets with dribble condition detected
8 packets output, 1658 bytes, 0 underruns
0 output errors, 0 collisions, 4 interface resets
0 babbles, 0 late collision, 0 deferred
0 lost carrier, 0 no carrier
0 output buffer failures, 0 output buffers swapped out
Router#
This example uses the show ip interface command to display the detailed configuration and status of Fast Ethernet interface 5/4:
Router# show ip interface fastethernet 5/4 FastEthernet5/4 is up, line protocol is up Internet address is 172.20.52.106/29 Broadcast address is 255.255.255.255 Address determined by setup command MTU is 1500 bytes Helper address is not set Directed broadcast forwarding is disabled Multicast reserved groups joined: 224.0.0.10 Outgoing access list is not set Inbound access list is not set Proxy ARP is enabled Security level is default Split horizon is enabled ICMP redirects are always sent ICMP unreachables are always sent ICMP mask replies are never sent IP fast switching is enabled IP fast switching on the same interface is disabled IP Flow switching is disabled IP CEF switching is enabled IP Fast switching turbo vector IP Normal CEF switching turbo vector IP multicast fast switching is enabled IP multicast distributed fast switching is disabled Router Discovery is disabled IP output packet accounting is disabled IP access violation accounting is disabled TCP/IP header compression is disabled RTP/IP header compression is disabled Probe proxy name replies are disabled Policy routing is disabled Network address translation is disabled WCCP Redirect outbound is disabled WCCP Redirect exclude is disabled BGP Policy Mapping is disabled IP multicast multilayer switching is disabled IP mls switching is enabled Router#
This example uses the show running-config command to display the interface IP address configuration of Fast Ethernet interface 5/4:
Router# show running-config interfaces fastethernet 5/4 Building configuration... Current configuration: ! interface FastEthernet5/4 description "Router port" ip address 172.20.52.106 255.255.255.248 no ip directed-broadcast !
.
To configure IP routing, perform this task:
| Step | Command | Purpose | ||
|---|---|---|---|---|
| Router(config)# ip routing | Enable IP routing. (Required only if IP routing is disabled.) | ||
| Router(config)# router ip_routing_protocol | Specify an IP routing protocol. This step might include other commands, such as specifying the networks to route with the network command. Refer to the IOS Network Protocols Configuration Guide, Part 1. | ||
| Router(config)# end | Exit configuration mode. | ||
| Router# copy running-config startup-config | Save your configuration changes to NVRAM. |
This example shows how to enable IP routing:
Router# configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router(config)# ip routing Router(config)# router rip Router(config-router)# network 10.0.0.0 Router(config-router)# end Router#
To configure routing for Internetwork Packet Exchange (IPX), perform this task:
| Step | Command | Purpose | ||
|---|---|---|---|---|
| Router(config)# ipx routing | Enable IPX routing. | ||
| Router(config)# router ipx_routing_protocol | Specify an IP routing protocol. This step might include other commands, such as specifying the networks to route with the network command. Refer to the IOS Network Protocols Configuration Guide, Part 2. | ||
| Router(config)# interface {vlan vlan_ID} | {{ethernet | fastethernet | gigabitethernet} slot/port} | {port-channel port_channel_number}
| Select an interface to configure. | ||
| Router(config-if)# ipx network [network | unnumbered] encapsulation encapsulation-type | Configure the IPX network number. This enables IPX routing on the interface. When you enable IPX routing on the interface, you can also specify an encapsulation type. | ||
| Router(config-if)# no shutdown | Enable the interface. | ||
| Router(config-if)# end | Exit configuration mode. | ||
| Router# copy running-config startup-config | Save your configuration changes to NVRAM. |
This example shows how to enable IPX routing, create a VLAN interface, and assign the interface an IPX network address:
Router# configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router(config)# ipx routing Router(config)# ipx router rip Router(config-ipx-router)# network all Router(config-ipx-router)# interface vlan100 Router(config-if)# ipx network 100 encapsulation snap Router(config-if)# no shutdown Router(config-if)# end Router# copy running-config startup-config
To configure routing for AppleTalk, perform this task beginning in global configuration mode:
| Step | Command | Purpose | ||
|---|---|---|---|---|
| Router(config)# appletalk routing | Enable AppleTalk routing. Refer to the IOS Network Protocols Configuration Guide, Part 2. | ||
| Router(config)# interface {vlan vlan_ID} | {{ethernet | fastethernet | gigabitethernet} slot/port} | {port-channel port_channel_number}
| Select an interface to configure. | ||
| Router(config-if)# appletalk cable-range cable_range | Assign a cable range to the interface. | ||
| Router(config-if)# appletalk zone zone_name | Assign a zone name to the interface. | ||
| Router(config-if)# no shutdown | Enable the interface. | ||
| Router(config-if)# end | Exit configuration mode. | ||
| Router# copy running-config startup-config | Save your configuration changes to NVRAM. |
This example shows how to enable AppleTalk routing, create a VLAN interface, and assign the interface an AppleTalk cable-range and zone name:
Router# configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router(config)# appletalk routing Router(config)# interface vlan100 Router(config-if)# appletalk cable-range 100-100 Router(config-if)# appletalk zone Engineering Router(config-if)# no shutdown Router(config-if)# end Router# copy running-config startup-config
To enable Maintenance Operation Protocol (MOP) on an interface, perform this task:
| Command | Purpose |
|---|---|
Router(config-if)# mop enabled | Enable MOP. |
To enable an interface to send out periodic MOP system identification messages on an interface, perform this task:
| Command | Purpose |
|---|---|
Router(config-if)# mop sysid | Enable MOP message support. |
For detailed MOP configuration information, refer to the IOS Network Protocols Configuration Guide, Part 3.
Each interface has a hold-queue limit. This limit is the number of data packets that the interface can store in its hold queue before rejecting new packets. When the interface empties one or more packets from the hold queue, it can accept new packets again. To specify the hold-queue limit of an interface, perform this task:
| Command | Purpose |
|---|---|
Router(config-if)# hold-queue length {in | out} | Specify the maximum number of packets allowed in the hold queue. |
Higher-level protocols might use delay information to make operating decisions. For example, Interior Gateway Routing Protocol (IGRP) can use delay information to differentiate between a satellite link and a land link. To set a delay value for an interface, perform this task:
| Command | Purpose |
|---|---|
Router(config-if)# delay tens-of-microseconds | Set a delay value for an interface. |
Setting the delay value sets an informational parameter only; you cannot adjust the actual delay of an interface with this configuration command.
To adjust the frequency of update messages, perform this task:
| Command | Purpose |
|---|---|
Router(config-if)# keepalive [seconds] | Adjust the frequency with which the Cisco IOS software sends messages to itself to ensure that a network interface is alive. |
This example shows how to set the frequency of keepalive messages to 20 seconds on Fast Ethernet interface 5/5:
Router(config)# interface fastethernet 5/5 Router(config-if)# keepalive 20 Router(config-if)# *Sep 30 09:39:54: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet5/5, changed state to up Router(config-if)#
You also can configure the keepalive interval, the frequency at which the Cisco IOS software sends messages to itself (Ethernet) or to the other end (HDLC-serial, PPP-serial), to ensure that a network interface is alive. The interval is adjustable in 1-second increments down to 1-second. An interface is declared down after three update intervals have passed without receiving a keepalive packet.
When adjusting the keepalive timer for a very low bandwidth interface, large packets can delay the smaller keepalive packets long enough to cause the line protocol to go down. You might need to experiment to determine the best value.
Each interface has a default maximum packet size or maximum transmission unit (MTU) size. This number generally defaults to 1500 bytes. On serial interfaces, the MTU size varies, but cannot be set smaller than 64 bytes. To adjust the maximum packet size, perform this task:
| Command | Purpose |
|---|---|
Router(config-if)# mtu bytes | Adjust the maximum packet size or MTU size. |
This example shows how to configure the MTU on Fast Ethernet interface 5/5:
Router(config)# interface fastethernet 5/5 Router(config-if)# mtu 1500
Posted: Mon Jan 3 14:22:02 PST 2000
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