Configuring Layer 3 Interfaces
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Table Of Contents

Configuring Layer 3 Interfaces

Layer 3 Interface Configuration Guidelines and Restrictions

Configuring Subinterfaces on Layer 3 Interfaces

Configuring IPv4 Routing and Addresses

Configuring IPX Routing and Network Numbers

Configuring AppleTalk Routing, Cable Ranges, and Zones

Configuring Other Protocols on Layer 3 Interfaces


Configuring Layer 3 Interfaces

This chapter contains information about how to configure Layer 3 interfaces in Cisco IOS Software Release 12.2SX.

Note For complete syntax and usage information for the commands used in this chapter, see these publications:

•The Cisco IOS Software Releases 12.2SX Command References at this URL:

http://www.cisco.com/en/US/docs/ios/mcl/122sx_mcl.html

•The Release 12.2 publications at this URL:

http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/index.htm

This chapter consists of these sections:

•Layer 3 Interface Configuration Guidelines and Restrictions

•Configuring Subinterfaces on Layer 3 Interfaces

•Configuring IPv4 Routing and Addresses

•Configuring IPX Routing and Network Numbers

•Configuring AppleTalk Routing, Cable Ranges, and Zones

•Configuring Other Protocols on Layer 3 Interfaces

Layer 3 Interface Configuration Guidelines and Restrictions

When configuring Layer 3 interfaces, follow these guidelines and restrictions:

•We recommend that you configure no more than 2,000 Layer 3 VLAN interfaces.

•The ip unnumbered command is supported on Layer 3 VLAN interfaces.

•To support VLAN interfaces, create and configure VLANs and assign VLAN membership to Layer 2 LAN ports. For more information, see Chapter 17, "Configuring VLANs" and Chapter 16, "Configuring VTP."

•Cisco IOS Software Release 12.2SX does not support:

–Integrated routing and bridging (IRB)

–Concurrent routing and bridging (CRB)

–Remote source-route bridging (RSRB)

•Use bridge groups on VLAN interfaces, sometimes called fall-back bridging, to bridge nonrouted protocols. Bridge groups on VLAN interfaces are supported in software on the route processor (RP).

•Cisco IOS Software Release 12.2SX does not support the IEEE bridging protocol for bridge groups. Configure bridge groups to use the VLAN-bridge or the DEC spanning-tree protocol.

Configuring Subinterfaces on Layer 3 Interfaces

When configuring Layer 3 subinterfaces, follow these guidelines and restrictions:

•The PFC3 supports these features on LAN port subinterfaces:

–IPv4 unicast forwarding, including MPLS VPN

–IPv4 multicast forwarding, including MPLS VPN

–6PE

–EoMPLS

–IPv4 unnumbered

–Counters for subinterfaces in MIBS and with the show vlans command

–iBGP and eBGP

–OSPF

–EIGRP

–RIPv1/v2

–RIPv2

–ISIS

–Static routing

–Unidirectional link routing (UDLR)

–IGMPv1, IGMPv2, IGMPv3

–PIMv1, PIMv2

–SSM IGMPv3lite and URD

–Stub IP multicast routing

–IGMP join

–IGMP static group

–Multicast routing monitor (MRM)

–Multicast source discovery protocol (MSDP)

–SSM

–IPv4 Ping

–IPv6 Ping

•Always use the native keyword when the VLAN ID is the ID of the IEEE 802.1Q native VLAN. Do not configure encapsulation on the native VLAN of an IEEE 802.1Q trunk without the native keyword.

•Because VLAN IDs are global to the switch, you can use a VLAN internally, on a subinterface, or with a Layer 3 VLAN interface.

–You cannot configure an internal VLAN on a subinterface or a Layer 3 VLAN interface.

–You cannot configure a subinterface VLAN on a Layer 3 VLAN interface.

–You cannot configure a VLAN used with a Layer 3 VLAN interface on a subinterface.

Note You cannot configure a VLAN used on one interface or subinterface on another interface or subinterface.

•You can configure subinterfaces with any normal range or extended range VLAN ID in VTP transparent mode. Because VLAN IDs 1 to 1005 are global in the VTP domain and can be defined on other network devices in the VTP domain, you can use only extended range VLANs with subinterfaces in VTP client or server mode. In VTP client or server mode, normal range VLANs are excluded from subinterfaces.

Note If you configure normal range VLANs on subinterfaces, you cannot change the VTP mode from transparent.

To configure a subinterface, perform this task:

 
Command
Purpose

Step 1 

Router> enable

Enters privileged EXEC mode.

Step 2 

Router# configure terminal

Enters global configuration mode.

Step 3 

Router(config)# interface {{type1  slot/port.subinterface} | {port-channel port_channel_number.subinterface}}

Selects an interface and enters subinterface configuration mode.

Step 4 

Router(config-subif)# encapsulation dot1q vlan_ID [native]

Configures 802.1Q encapsulation for the subinterface.

Step 5 

Router(config-if)# exit

Returns to global configuration mode.

1 type = fastethernet, gigabitethernet, tengigabitethernet, or ge-wan

Configuring IPv4 Routing and Addresses

For complete information and procedures, see these publications:

•Cisco IOS IP and IP Routing Configuration Guide, Release 12.2, at this URL:

http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fipr_c/index.htm

•Cisco IOS IP and IP Routing Command Reference, Release 12.2, at these URLs:

http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fipras_r/index.htm

http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fiprrp_r/index.htm

When configuring IPv4 routing and addresses, follow these guidelines and restrictions:

•For information about the maximum paths command, see the Cisco IOS Software Releases 12.2SX Command References publication.

•The Policy Feature Card (PFC) and any Distributed Feature Cards (DFCs) provide hardware support for policy-based routing (PBR) for route-map sequences that use the match ip address, set ip next-hop, and ip default next-hop PBR keywords.

When configuring PBR, follow these guidelines and restrictions:

–The PFC provides hardware support for PBR configured on a tunnel interface.

–The PFC does not provide hardware support for PBR configured with the set ip next-hop keywords if the next hop is a tunnel interface.

–If the RP address falls within the range of a PBR ACL, traffic addressed to the RP is policy routed in hardware instead of being forwarded to the RP. To prevent policy routing of traffic addressed to the RP, configure PBR ACLs to deny traffic addressed to the RP.

–Any options in Cisco IOS ACLs that provide filtering in a PBR route-map that would cause flows to be sent to the RP to be switched in software are ignored. For example, logging is not supported in ACEs in Cisco IOS ACLs that provide filtering in PBR route-maps.

–PBR traffic through switching module ports where PBR is configured is routed in software if the switching module resets. (CSCee92191)

–Any permit route-map sequence with no set statement will cause matching traffic to be processed by the RP.

To configure PBR, see the Cisco IOS Quality of Service Solutions Configuration Guide, Release 12.2, "Classification," "Configuring Policy-Based Routing," at this URL:

http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fqos_c/fqcprt1/qcfpbr.htm

To configure IPv4 routing and an IPv4 address on a Layer 3 interface, perform this task:

 
Command
Purpose

Step 1 

Router(config)# ip routing

Enables IPv4 routing. (Required only if IPv4 routing is disabled.)

Step 2 

Router(config)# router ip_routing_protocol

Specifies an IPv4 routing protocol.

Step 3 

Router(config-router)# ip_routing_protocol_commands

Configures the IPv4 routing protocol.

Step 4 

Router(config-router)# exit

Exists IPv4 routing protocol configuration mode.

Step 5 

Router(config)# interface {vlan vlan_ID} | {type1  slot/port} | {port-channel port_channel_number}

Selects an interface to configure.

Step 6 

Router(config-if)# ip address ip_address subnet_mask

Configures the IPv4 address and IPv4 subnet.

Step 7 

Router(config-if)# no shutdown

Enables the interface.

Step 8 

Router(config-if)# end

Exits configuration mode.

Step 9 

Router# show interfaces [{vlan vlan_ID} | {type1 slot/port} | {port-channel port_channel_number}]

Router# show ip interfaces [{vlan vlan_ID} | {type1 slot/port} | {port-channel port_channel_number}]

Router# show running-config interfaces [{vlan vlan_ID} | {type1 slot/port} | {port-channel port_channel_number}]

Verifies the configuration.

1 type = fastethernet, gigabitethernet, or tengigabitethernet

This example shows how to enable IPv4 Routing Information Protocol (RIP) 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#

This example shows how to configure an IPv4 address on Fast Ethernet port 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)# end 

Router#

This example uses the show interfaces command to display the interface IPv4 address configuration and status of Fast Ethernet port 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 port 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 IPv4 address configuration of Fast Ethernet port 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

!

Configuring IPX Routing and Network Numbers

Note The RP supports IPX with fast switching.

For complete information and procedures, see these publications:

•Cisco IOS AppleTalk and Novell IPX Configuration Guide, Release 12.2, at this URL:

http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fatipx_c/index.htm

•Cisco IOS AppleTalk and Novell IPX Command Reference, Release 12.2, at this URL:

http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fatipx_r/index.htm

To configure routing for Internetwork Packet Exchange (IPX) and configure IPX on a Layer 3 interface, perform this task:

 
Command
Purpose

Step 1 

Router(config)# ipx routing

Enables IPX routing.

Step 2 

Router(config)# router ipx_routing_protocol

Specifies an IP routing protocol. This step might include other commands, such as specifying the networks to route with the network command.

Step 3 

Router(config)# interface {vlan vlan_ID} | {type1  slot/port} | {port-channel port_channel_number}

Selects an interface to configure.

Step 4 

Router(config-if)# ipx network [network | unnumbered] encapsulation encapsulation_type

Configures 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.

Step 5 

Router(config-if)# no shutdown

Enables the interface.

Step 6 

Router(config-if)# end

Exits configuration mode.

Step 7 

Router# show interfaces [{vlan vlan_ID} | {type1 slot/port} | {port-channel port_channel_number}]

Router# show ipx interfaces [{vlan vlan_ID} | {type1 slot/port} | {port-channel port_channel_number}]

Router# show running-config interfaces [{vlan vlan_ID} | {type1 slot/port} | {port-channel port_channel_number}]

Verifies the configuration.

1 type = fastethernet, gigabitethernet, or tengigabitethernet

This example shows how to enable IPX routing and assign an IPX network address to interface VLAN 100: 

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 vlan 100 

Router(config-if)# ipx network 100 encapsulation snap 

Router(config-if)# no shutdown 

Router(config-if)# end 

Router# copy running-config startup-config

Configuring AppleTalk Routing, Cable Ranges, and Zones

For complete information and procedures, see these publications:

•Cisco IOS AppleTalk and Novell IPX Configuration Guide, Release 12.2, at this URL:

http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fatipx_c/index.htm

•Cisco IOS AppleTalk and Novell IPX Command Reference, Release 12.2, at this URL:

http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fatipx_r/index.htm

To configure routing for AppleTalk, perform this task beginning in global configuration mode:

 
Command
Purpose

Step 1 

Router(config)# appletalk routing

Enables AppleTalk routing.

Step 2 

Router(config)# interface {vlan vlan_ID} | {type1  slot/port} | {port-channel port_channel_number}

Selects an interface to configure.

Step 3 

Router(config-if)# appletalk cable-range cable_range

Assigns a cable range to the interface.

Step 4 

Router(config-if)# appletalk zone zone_name

Assigns a zone name to the interface.

Step 5 

Router(config-if)# no shutdown

Enables the interface.

Step 6 

Router(config-if)# end

Exits configuration mode.

Step 7 

Router# show interfaces [{vlan vlan_ID} | {type1 slot/port} | {port-channel port_channel_number}]

Router# show appletalk interfaces [{vlan vlan_ID} | {type1 slot/port} | {port-channel port_channel_number}]

Router# show running-config interfaces [{vlan vlan_ID} | {type1 slot/port} | {port-channel port_channel_number}]

Verifies the configuration.

1 type = fastethernet, gigabitethernet, or tengigabitethernet

This example shows how to enable AppleTalk routing and assign an AppleTalk cable-range and zone name to interface VLAN 100: 

Router# configure terminal

Enter configuration commands, one per line.  End with CNTL/Z.

Router(config)# appletalk routing

Router(config)# interface vlan 100

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

Configuring Other Protocols on Layer 3 Interfaces

See these publications for information about configuring other protocols on Layer 3 interfaces:

•Cisco IOS Apollo Domain, VINES, DECnet, ISO CLNS, and XNS Configuration Guide, Release 12.2, at this URL:

http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fapolo_c/index.htm

•Cisco IOS Apollo Domain, VINES, DECnet, ISO CLNS, and XNS Command Reference, Release 12.2, at this URL:

http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fapolo_r/index.htm