Implementing Frame Mode MPLS

Date: Jun 16, 2008 By Scott Empson, Hans Roth. Sample Chapter is provided courtesy of Cisco Press.

This chapter covers configuring Cisco Express Forwarding, verifying CEF, troubleshooting CEF, configuring MPLS on a Frame Mode interface, and configuring MTU size in label switching.

This chapter provides information and commands concerning the following topics:

Configuring Cisco Express Forwarding
- - Verifying CEF
- - Troubleshooting CEF
Configuring MPLS on a Frame Mode interface
Configuring MTU size in label switching

Configuring Cisco Express Forwarding

To enable MPLS, you must first enable Cisco Express Forwarding (CEF) switching.

`Router(config)#``ip cef`	Enables standard CEF
`Router(config)#``ip cef distributed`	Enables dCEF
`Router(config)#``no ip cef`	Disables CEF globally
`Router(config)#``interface fastethernet 0/1`	Moves to interface configuration mode
`Router(config-if)#``ip route-cache cef`	Enables CEF on the interface

Verifying CEF

`Router#``show ip cef`	Displays entries in the forwarding information base (FIB)
`Router#``show ip cef summary`	Displays a summary of the FIB
`Router#``show ip cef unresolved`	Displays unresolved FIB entries
`Router#``show ip cef fastethernet 0/1`	Displays the FIB entry for the specified interface
`Router#``show ip cef fastethernet 0/1 detail`	Displays detailed information about the FIB for the interface
`Router#``show cef drop`	Displays packets that are dropped due to adjacencies that are incomplete or nonexistent

Troubleshooting CEF

`Router#``debug ip cef`	Displays debug information for CEF
`Router#``debug ip cef drop`	Displays debug information about dropped packets
`Router#``debug ip cef access-list` `x`	Displays information from specified access lists
`Router#``debug ip cef receive`	Displays information about packets received by IP CEF
`Router#``debug ip cef events`	Displays general CEF events
`Router#``debug ip cef prefix-ipc`	Displays updates related to IP prefix information
`Router#``debug ip cef table`	Produces a table showing events related to the FIB table

Configuring MPLS on a Frame Mode Interface

`Router(config)#``mpls ip`	Enables MPLS globally on the router NOTE: MPLS is enabled by default on Cisco routers. However, if you need to re-enable it, use the global mpls ip command.
`Router(config)#``interface fastethernet 0/0`	Moves to interface configuration mode
`Router(config-if)#``mpls ip`	Enables MPLS on the specified interface
`Router(config-if)#``mpls label protocol tdp`	Enables Tag Distribution Protocol (TDP) on this interface NOTE: TDP is Cisco proprietary. LDP is a superset of TDP. Cisco is changing from TDP to a fully compliant LDP.
`Router(config-if)#``mpls label protocol ldp`	Enables Label Distribution Protocol (LDP) on this interface NOTE: LDP is the default protocol on Cisco IOS Release 12.4(3) and later. In older releases, TDP was the default protocol.
`Router(config-if)#``mpls label protocol both`	Enables both TDP and LDP on this interface

Configuring MTU Size in Label Switching

Router(config)# interface fasthethernet 0/0

Moves to interface configuration mode

Router(config-if)# mpls mtu 1512

Changes the maximum size of an MPLS-labeled packet to 1512 bytes

NOTE: The mpls mtu command is an optional command when working with MPLS. But because of the addition of the label header, the MTU on LAN interfaces should be increased to prevent IP fragmentation.

NOTE: The minimum MTU is 64 bytes. The maximum MTU depends on the type of interface medium that is being used.

Configuration Example: Configuring Frame Mode MPLS

Figure 3-1 shows the network topology for the configuration that follows, which shows how to configure Frame Mode MPLS using commands covered in this chapter.

Figure 3-1 Network Topology for Frame Mode MPLS Configuration Example

R1 Router

`Router>``enable`	Moves to privileged mode
`Router#``configure terminal`	Moves to global configuration mode
`Router(config)#``hostname R1`	Assigns hostname to router
`R1(config)#``ip cef`	Enables CEF on device (enabled by default)
`R1(config)#``mpls ip`	Enables MPLS globally on device (enabled by default)
`R1(config)#``interface loopback 0`	Moves to interface configuration mode
`R1(config-if)#``ip address 172.16.1.1 255.255.255.0`	Assigns IP address and netmask
`R1(config-if)#``interface fastethernet 0/0`	Moves to interface configuration mode
`R1(config-if)#``ip address 172.16.10.1 255.255.255.0`	Assigns IP address and netmask
`R1(config-if)#``mpls ip`	Enables MPLS on this interface
`R1(config-if)#``mpls mtu 1508`	Changes the maximum size of the packet allowed on this interface to 1508 bytes
`R1(config-if)#``no shutdown`	Activates interface
`R1(config-if)#``exit`	Returns to global configuration mode
`R1(config)#``router eigrp 1`	Enables the EIGRP routing process for AS 1
`R1(config-router)#``network 172.16.0.0`	Specifies which network to advertise in EIGRP
`R1(config-router)#``no auto-summary`	Turns off the auto-summarization feature
`R1(config-router)#``exit`	Returns to global configuration mode
`R1(config)#``exit`	Returns to privileged mode
`R1#``copy running-config startup-config`	Saves configuration in NVRAM

R2 Router

`Router>``enable`	Moves to privileged mode
`Router#``configure terminal`	Moves to global configuration mode
`Router(config)#``hostname R2`	Assigns hostname to router
`R2(config)#``ip cef`	Enables CEF on device (enabled by default)
`R2(config)#``mpls ip`	Enables MPLS globally on device (enabled by default)
`R2(config)#``interface loopback 0`	Moves to interface configuration mode
`R2(config-if)#``ip address 172.16.2.1 255.255.255.0`	Assigns IP address and netmask
`R2(config-if)#``interface fastethernet 0/0`	Moves to interface configuration mode
`R2(config-if)#``ip address 172.16.10.2 255.255.255.0`	Assigns IP address and netmask
`R2(config-if)#``mpls ip`	Enables MPLS on this interface
`R2(config-if)#``mpls mtu 1508`	Changes the maximum size of the packet allowed on this interface to 1508 bytes
`R2(config-if)#``no shutdown`	Activates interface
`R2(config-if)#``interface serial 0/0/0`	Moves to interface configuration mode
`R2(config-if)#``ip address 172.16.20.5 255.255.255.252`	Assigns IP address and netmask
`R2(config-if)#``mpls ip`	Enables MPLS on this interface
`R2(config-if)#``clock rate 64000`	Enables clock rate for this interface
`R2(config-if)#``no shutdown`	Activates interface
`R2(config-if)#``exit`	Returns to global configuration mode
`R2(config)#``router eigrp 1`	Enables the EIGRP routing process for AS 1
`R2(config-router)#``network 172.16.0.0`	Specifies which network to advertise in EIGRP
`R2(config-router)#``no auto-summary`	Turns off the auto-summarization feature
`R2(config-router)#``exit`	Returns to global configuration mode
`R2(config)#``exit`	Returns to privileged mode
`R2#``copy running-config startup-config`	Saves configuration in NVRAM

R3 Router

`Router>``enable`	Moves to privileged mode
`Router#``configure terminal`	Moves to global configuration mode
`Router(config)#``hostname R3`	Assigns hostname to router
`R3(config)#``ip cef`	Enables CEF on device (enabled by default)
`R3(config)#``mpls ip`	Enables MPLS globally on device (enabled by default)
`R3(config)#``interface loopback 0`	Moves to interface configuration mode
`R3(config-if)#``ip address 172.16.3.1 255.255.255.0`	Assigns IP address and netmask
`R3(config-if)#``interface serial 0/0/0`	Moves to interface configuration mode
`R3(config-if)#``ip address 172.16.20.6 255.255.255.252`	Assigns IP address and netmask
`R3(config-if)#``mpls ip`	Enables MPLS on this interface
`R3(config-if)#``no shutdown`	Activates interface
`R3(config-if)#``exit`	Returns to global configuration mode
`R3(config)#``router eigrp 1`	Enables the EIGRP routing process for AS 1
`R3(config-router)#``network 172.16.0.0`	Specifies which network to advertise in EIGRP
`R3(config-router)#``no auto-summary`	Turns off the auto-summarization feature
`R3(config-router)#``exit`	Returns to global configuration mode
`R3(config)#``exit`	Returns to privileged mode
`R3#``copy running-config startup-config`	Saves configuration in NVRAM