Example: Configuring LDP-Signaled LSPs

This example shows how to create and configure LDP instances within an MPLS network.

• Requirements
• Overview
• Configuration
• Verification

Requirements

Before you begin:

1. Configure network interfaces. See the Junos OS Interfaces Configuration Guide for Security Devices.
2. Configure an IGP across your network. (The LDP configuration is added to the existing IGP configuration and included in the MPLS configuration.)
3. Configure a network to use LDP for LSP establishment by enabling MPLS on all transit interfaces in the MPLS network.

   Note: Because LDP runs on top of an IGP such as IS-IS or OSPF, you must configure LDP and the IGP on the same set of interfaces.

Overview

To configure LDP-signaled RSPs, you must enable the MPLS family on all transit interfaces in the MPLS network, enable the MPLS process on all router interfaces in the MPLS network, and enable an LDP instance on each router. In this example, you enable the MPLS family and create an LDP instance on the ge-0/0/0 interface. Additionally, you enable the MPLS process on all router interfaces in the MPLS network.

Configuration

CLI Quick Configuration

To quickly configure LDP instances within an MPLS network, copy the following commands and paste them into the CLI.

Step-by-Step Procedure

To enable LDP instances within an MPLS network:

1. Enable the MPLS family on the transit interface.
   [edit]user@host# set interfaces ge-0/0/0 unit 0 family mpls
2. Enable the MPLS process all interfaces.
   [edit]user@host# set protocols mpls interface all
3. Create the LDP instance on the transit interface.
   [edit]user@host# set protocols ldp interface ge-0/0/0

Results

Confirm your configuration by entering the show command from configuration mode. If the output does not display the intended configuration, repeat the configuration instructions in this example to correct it.

For brevity, this show output includes only the configuration that is relevant to this example. Any other configuration on the system has been replaced with ellipses (...).

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

Results

Verification

To confirm that the configuration is working properly, perform these tasks:

• Verifying LDP Neighbors
• Verifying LDP Sessions
• Verifying the Presence of LDP-Signaled LSPs
• Verifying Traffic Forwarding over the LDP-Signaled LSP

Verifying LDP Neighbors

Purpose

Verify that each router shows the appropriate LDP neighbors.

Action

From the CLI, enter the show ldp neighbor command.

Sample Output

Address     Interface       Label space ID      Hold time
10.0.8.5    ge-0/0/0.0      10.0.9.6:0            14
10.0.8.10   ge-0/0/1.0      10.0.9.7:0            11

Meaning

The output shows the IP addresses of the neighboring interfaces along with the interface through which the neighbor adjacency is established. Verify the following information:

• Each interface on which LDP is enabled is listed.
• Each neighboring LDP interface address is listed with the appropriate corresponding LDP interface.
• Under Label space ID, the appropriate loopback address for each neighbor appears.

Verifying LDP Sessions

Purpose

Verify that a TCP-based LDP session has been established between all LDP neighbors. Also, verify that the modified keepalive value is active.

Action

From the CLI, enter the show ldp session detail command.

Sample Output

Address: 10.0.9.7, State: Operational, Connection: Open, Hold time: 28
  Session ID: 10.0.3.5:0--10.0.9.7:0
  Next keepalive in 3 seconds
  Passive, Maximum PDU: 4096, Hold time: 30, Neighbor count: 1
  Keepalive interval: 10, Connect retry interval: 1
  Local - Restart: disabled, Helper mode: enabled
  Remote - Restart: disabled, Helper mode: disabled
  Local maximum recovery time: 240000 msec
  Next-hop addresses received:
    10.0.8.10
    10.0.2.17

Meaning

The output shows the detailed information, including session IDs, keepalive interval, and next-hop addresses, for each established LDP session. Verify the following information:

• Each LDP neighbor address has an entry, listed by loopback address.
• The state for each session is Operational, and the connection for each session is Open. A state of Nonexistent or a connection of Closed indicates a problem with one of the following:
  • LDP configuration
  • Passage of traffic between the two devices
  • Physical link between the two routers
• For Keepalive interval, the appropriate value, 10, appears.

Verifying the Presence of LDP-Signaled LSPs

Purpose

Verify that each Juniper Networks device's inet.3 routing table has an LSP for the loopback address on each of the other routers.

Action

From the CLI, enter the show route table inet.3 command.

Sample Output

inet.3: 2 destinations, 2 routes (2 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both

10.0.9.6/32         *[LDP/9/0] 00:05:29, metric 1
                    > to 10.0.8.5 via ge-0/0/0.0
10.0.9.7/32         *[LDP/9/0] 00:05:37, metric 1
                    > to 10.0.8.10 via ge-0/0/1.0

Meaning

The output shows the LDP routes that exist in the inet.3 routing table. Verify that an LDP-signaled LSP is associated with the loopback addresses of the other routers in the MPLS network.

Verifying Traffic Forwarding over the LDP-Signaled LSP

Purpose

Verify that traffic between hosts is forwarded over the LDP-signaled LSP. Because traffic uses any configured gateway address by default, you must explicitly specify that the gateway address is to be bypassed.

Action

From the CLI, enter the traceroute 220.220.0.0 source 200.200.0.1 bypass-routing gateway 172.16.0.1 command.

Sample Output

traceroute to 220.220.0.1 (172.16.0.1) from 200.200.0.1, 30 hops max, 40 byte packets
 1  172.16.0.1 (172.16.0.1)  0.661 ms  0.538 ms  0.449 ms
 2  10.0.8.9 (10.0.8.9)  0.511 ms  0.479 ms  0.468 ms
    MPLS Label=100004 CoS=0 TTL=1 S=1
 3  10.0.8.5 (10.0.8.5)  0.476 ms  0.512 ms  0.441 ms
 4  220.220.0.1 (220.220.0.1)  0.436 ms  0.420 ms  0.416 ms

Meaning

The output shows the route that traffic travels between hosts without using the default gateway. In this example, verify that traffic sent from Host C1 to Host C2 travels through Router R7. The 10.0.8.9 address is the interface address for Router R5.

Related Topics

• Junos OS Feature Support Reference for SRX Series and J Series Devices
• Understanding the LDP Signaling Protocol
• Junos OS Routing Protocols and Policies Configuration Guide for Security Devices
• show ldp neighbor in the Junos Routing Protocols and Policies Command Reference
• show ldp session in the Junos Routing Protocols and Policies Command Reference
• show route table in the Junos Routing Protocols and Policies Command Reference
• traceroute in the Junos System Basics and Services Command Reference