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Example: Advertising Label-Switched Paths into IS-IS

Understanding Forwarding Adjacencies

When you set up MPLS traffic-engineering tunnels between sites, by default the IGP does not consider those tunnels for traffic forwarding. Forwarding adjacencies allow you to treat a traffic engineering LSP tunnel as a link in an IGP topology. The link is used in the shortest-path-first (SPF) algorithm and is advertised to the IGP peers. A forwarding adjacency can be created between routing devices regardless of their location in the network.

Example: Advertising Label-Switched Paths into IS-IS

This example shows how to advertise label-switched paths (LSPs) into IS-IS as point-to-point links (sometimes referred to as forwarding adjacencies) so that the LSPs can be used in SPF calculations. The advertisement contains a local address (the from address of the LSP), a remote address (the to address of the LSP), and a metric.

• Requirements
• Overview
• Configuration
• Verification

Requirements

No special configuration beyond device initialization is required before configuring this example.

Overview

Figure 1 shows the topology used in this example.

Figure 1: IS-IS Advertising a Label-Switched Path Topology

The example shows how to configure the LSP from Device E to Device D and then advertise this path through IS-IS. The configuration is verified by performing a traceroute operation from Device A to Device D and making sure that the LSP is used for forwarding.

CLI Quick Configuration shows the configuration for all of the devices in Figure 1. The section Step-by-Step Procedure describes the steps on Device E.

Configuration

CLI Quick Configuration

To quickly configure this example, copy the following commands, paste them into a text file, remove any line breaks, change any details necessary to match your network configuration, and then copy and paste the commands into the CLI at the [edit] hierarchy level.

Step-by-Step Procedure

1. Configure the interfaces.
   [edit interfaces]user@E# set fe-1/2/0 unit 0 family inet address 10.0.0.2/30user@E# set fe-1/2/0 unit 0 family isouser@E# set fe-1/2/0 unit 0 family mplsuser@E# set fe-1/2/1 unit 0 family inet address 10.0.0.17/30user@E# set fe-1/2/1 unit 0 family isouser@E# set fe-1/2/1 unit 0 family mplsuser@E# set lo0 unit 0 family inet address 192.168.0.5/32user@E# set lo0 unit 0 family iso address 49.0002.0192.0168.0005.00
2. Enable a signaling protocol on the interfaces.
   [edit protocols rsvp]user@E# set interface lo0.0user@E# set interface fe-1/2/0.0user@E# set interface fe-1/2/1.0
3. Enable MPLS on the interfaces.
   [edit protocols mpls]user@E# set interface fe-1/2/0.0user@E# set interface fe-1/2/1.0
4. Configure the LSP.

   Make sure that you configure the reverse LSP on the endpoint, in this case on Device D.

   [edit protocols mpls]user@E# set label-switched-path E-D to 192.168.0.4
5. Configure internal BGP (IBGP) peering among the devices that must run MPLS.
   [edit protocols bgp group int]user@E# set type internaluser@E# set local-address 192.168.0.5user@E# set neighbor 192.168.0.6user@E# set neighbor 192.168.0.1user@E# set neighbor 192.168.0.4
6. Enable IS-IS on the interfaces, and set the link metric.

   IS-IS Level 1 and Level 2 are enabled when you include the interface at [edit protocols isis]. By disabling Level 1, you are in effect creating a Level 2 IS-IS interface.

   [edit protocols isis]user@E# set interface fe-1/2/0.0 level 1 disableuser@E# set interface fe-1/2/1.0 level 1 disableuser@E# set interface fe-1/2/1.0 level 2 metric 20user@E# set interface lo0.0
7. Advertise the LSP through IS-IS.

   Make sure that you advertise the LSP on the endpoint, in this case on Device D.

   [edit protocols isis]user@E# set label-switched-path E-D level 2 metric 15
8. Configure the router ID and the autonomous system (AS) number.
   [edit routing-options]user@E# set router-id 192.168.0.5user@E# set autonomous-system 1

Results

From configuration mode, confirm your configuration by entering the show interfaces, show protocols, and show routing-options commands. If the output does not display the intended configuration, repeat the instructions in this example to correct the configuration.

If you are done configuring the device, enter commit from configuration mode.

Verification

Confirm that the configuration is working properly.

• Verifying the IS-IS Neighbor
• Checking the IS-IS SPF Calculations
• Checking the Forwarding Path

Verifying the IS-IS Neighbor

Purpose

Verify that another neighbor is listed and is reachable over the LSP. The interface field indicates the name of the LSP.

Action

From operational mode, enter the show isis adjacency detail command.

D
  Interface: E-D, Level: 2, State: One-way, Expires in 0 secs
  Priority: 0, Up/Down transitions: 1, Last transition: 1d 00:34:58 ago
  Circuit type: 3, Speaks: IP
  Topologies: Unicast
  Restart capable: No, Adjacency advertisement: Advertise
  IP addresses: 192.168.0.4

F
  Interface: fe-1/2/1.0, Level: 2, State: Up, Expires in 7 secs
  Priority: 64, Up/Down transitions: 1, Last transition: 1d 01:16:22 ago
  Circuit type: 2, Speaks: IP, IPv6, MAC address: 0:5:85:8f:c8:bd
  Topologies: Unicast
  Restart capable: Yes, Adjacency advertisement: Advertise
  LAN id: F.02, IP addresses: 10.0.0.18

A
  Interface: fe-1/2/0.0, Level: 2, State: Up, Expires in 20 secs
  Priority: 64, Up/Down transitions: 1, Last transition: 1d 01:17:20 ago
  Circuit type: 2, Speaks: IP, IPv6, MAC address: 0:5:85:8f:c8:bc
  Topologies: Unicast
  Restart capable: Yes, Adjacency advertisement: Advertise
  LAN id: E.02, IP addresses: 10.0.0.1

Meaning

As expected, Interface: E-D is shown in the output, and the state is shown as One-way.

Checking the IS-IS SPF Calculations

Purpose

Verify that the LSP is being used in the SPF calculations.

Action

From operational mode, enter the show isis spf brief command.

 IS-IS level 1 SPF results:
Node             Metric     Interface        NH   Via             SNPA
E.00         0
  1 nodes

 IS-IS level 2 SPF results:
Node             Metric     Interface        NH   Via             SNPA
C.02         30         fe-1/2/0.0       IPV4 A           0:5:85:8f:c8:bc
C.00         25         fe-1/2/1.0      LSP  E-D           
D.03         25         fe-1/2/1.0      LSP  E-D           
D.02         25         fe-1/2/1.0      LSP  E-D           
F.00         20         fe-1/2/1.0      IPV4 F           0:5:85:8f:c8:bd
B.00         20         fe-1/2/0.0       IPV4 A           0:5:85:8f:c8:bc
B.02         20         fe-1/2/0.0       IPV4 A           0:5:85:8f:c8:bc
D.00         15         fe-1/2/1.0      LSP  E-D           
A.00         10         fe-1/2/0.0       IPV4 A           0:5:85:8f:c8:bc
E.02         10
E.00         0
  11 nodes

Meaning

As expected, the SPF results include the LSP, E-D.

Checking the Forwarding Path

Purpose

Verify that a traceroute operation from Device A to Device D uses the LSP.

Action

traceroute to 192.168.0.4 (192.168.0.4), 30 hops max, 40 byte packets
 1  10.0.0.2 (10.0.0.2)  1.092 ms  1.034 ms  1.174 ms
 2  10.0.0.18 (10.0.0.18)  1.435 ms  2.062 ms  2.232 ms
     MPLS Label=299792 CoS=0 TTL=1 S=1
 3  bb04-cclab-lo0.spglab.juniper.net (192.168.0.4)  2.286 ms  1.432 ms  1.354 ms

Meaning

The output shows that the LSP is used.