Verifying an LDP-Signaled LSP

Suppose that LDP is configured to establish an LSP as shown in Figure 4.

To verify the LDP configuration, perform these verification tasks:

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

Purpose

Verify that each Services Router shows the appropriate LDP neighbors—for example, that Router R5 has both Router R6 and Router R7 as 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    fe-0/0/0.0      10.0.9.6:0            14
10.0.8.10   fe-0/0/1.0      10.0.9.7:0            11

What it Means

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.

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: 5, 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

What it Means

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 Services Routers
  • Physical link between the two routers
• For Keepalive interval, the appropriate value, 5, appears.

Purpose

Verify that each Services Router'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 fe-0/0/0.0
10.0.9.7/32         *[LDP/9/0] 00:05:37, metric 1
                    > to 10.0.8.10 via fe-0/0/1.0

What it Means

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.

Purpose

Verify that traffic between Hosts C1 and C2 is forwarded over the LDP-signaled LSP between Services Router R6 and Services Router R7. Because traffic uses any configured gateway address by default, you must explicitly specify that the gateway address is to be bypassed.

Action

If Host C1 is a Juniper Networks router, 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

What it Means

The output shows the route that traffic travels between Hosts C1 and C2, without using the default gateway. Verify that traffic sent from C1 to C2 travels through Router R7. The 10.0.8.9 address is the interface address for Router R5.