Tracing LDP Operations

Problem

You want to check that LDP is properly exchanging messages with its neighbors.

Solution

Set up a tracing file to capture information about the exchange of LDP protocol packets:

	[edit protocols ldp]
	aviva@RouterG# set traceoptions file ldp-log
	aviva@RouterG# set traceoptions flag packets

Discussion

One tool for troubleshooting LDP operation is the JUNOS tracing facility. If an LDP session that was operating properly suddenly stops working, you can trace the routers LDP packet exchanges with its neighbors to help track down the source of the problem. This recipe sets up an LDP-specific tracing file named ldp-log that captures all LDP packet exchanges with neighboring routers.

Use the show log command to see the file contents:

	aviva@RouterG> show log ldp-log
	Oct 5 19:25:46 Incredible-Hulk clear-log[15758]: logfile cleared
	Oct 5 19:25:48 LDP sent UDP PDU 10.0.0.1 -> 224.0.0.2 (t1-4/0/0.0)
	Oct 5 19:25:48 ver 1, pkt len 42, PDU len 38, ID 192.168.19.1:0
	Oct 5 19:25:48 Msg Hello (0x100), len 28, ID 396082
	Oct 5 19:25:48 TLV HelloParms (0x400), len 4
	Oct 5 19:25:48 TLV XportAddr (0x401), len 4
	Oct 5 19:25:48 TLV ConfSeq (0x402), len 4
	Oct 5 19:25:49 LDP rcvd UDP PDU 10.0.0.2 -> 224.0.0.2 (t1-4/0/0.0)
	Oct 5 19:25:49 ver 1, pkt len 42, PDU len 38, ID 192.168.17.1:0
	Oct 5 19:25:49 Msg Hello (0x100), len 28, ID 397238
	Oct 5 19:25:49 TLV HelloParms (0x400), len 4
	Oct 5 19:25:49 TLV XportAddr (0x401), len 4
	Oct 5 19:25:49 TLV ConfSeq (0x402), len 4
	Oct 5 19:25:52 LDP sent UDP PDU 10.0.0.1 -> 224.0.0.2 (t1-4/0/0.0)
	Oct 5 19:25:52 ver 1, pkt len 42, PDU len 38, ID 192.168.19.1:0
	Oct 5 19:25:52 Msg Hello (0x100), len 28, ID 396083
	Oct 5 19:25:52 TLV HelloParms (0x400), len 4
	Oct 5 19:25:52 TLV XportAddr (0x401), len 4
	Oct 5 19:25:52 TLV ConfSeq (0x402), len 4
	Oct 5 19:25:52  
LDP sent TCP PDU 192.168.19.1 -> 192.168.17.1 (none)
	Oct 5 19:25:52 ver 1, pkt len 18, PDU len 14, ID 192.168.19.1:0
	Oct 5 19:25:52 Msg Keepalive (0x201), len 4, ID 396084
	Oct 5 19:25:52  
LDP rcvd TCP PDU 192.168.17.1 -> 192.168.19.1 (none)
	Oct 5 19:25:52 ver 1, pkt len 18, PDU len 14, ID 192.168.17.1:0
	Oct 5 19:25:52 Msg Keepalive (0x201), len 4, ID 397241
	Oct 5 19:25:53 LDP rcvd 
UDP PDU 10.0.0.2 -> 224.0.0.2 (t1-4/0/0.0)
	Oct 5 19:25:53 ver 1, pkt len 42, PDU len 38, ID 192.168.17.1:0
	Oct 5 19:25:53 Msg Hello (0x100), len 28, ID 397242
	Oct 5 19:25:53 TLV HelloParms (0x400), len 4
	Oct 5 19:25:53 TLV XportAddr (0x401), len 4
	Oct 5 19:25:53 TLV ConfSeq (0x402), len 4

This log shows normal LDP operation. LDP is sending and receiving UDP and TCP messages with its neighboring routers. LDP multicasts UDP Hello messages to 224.0.0.2 to discover its neighbors. The log output shows that LDP is sending UDP hellos out the connection to the local subnet (10.0.0.1) and receiving hellos from the other end of the connection (10.0.0.2). LDP establishes TCP connections to exchange label and FEC information and sends periodic keepalive messages (every 10 seconds, by default) to its neighbors to keep the TCP session established. The logfile also shows that LDP is sending and receiving TCP keepalives from 192.168.17.1, the neighboring LDP router. All the entries in this logfile are what you would expect to see when an LDP session is operating properly.

When debugging LDP, you can set one or more of the following trace flags to capture LDP-related information:

	[edit protocols ldp]
	aviva@RouterG# set traceoptions flag ?
	Possible completions:
	 address Trace address packets
	 all Trace everything
	 binding Trace label binding state
	 error Trace errored packets
	 event Trace LDP state machine events
	 general Trace general events
	 initialization Trace initialization packets
	 label Trace label packets
	 normal Trace normal events
	 notification Trace notification packets
	 packets Trace all LDP packets
	 path Trace label path state
	 periodic Trace periodic (hello and keepalive) packets
	 policy Trace policy processing
	 route Trace routing information
	 state Trace state transitions
	 task Trace routing protocol task processing
	 timer Trace routing protocol timer processing

See Also

Recipe 5.10


Router Configuration and File Management

Basic Router Security and Access Control

IPSec

SNMP

Logging

NTP

Router Interfaces

IP Routing

Routing Policy and Firewall Filters

RIP

IS-IS

OSPF

BGP

MPLS

VPNs

IP Multicast



JUNOS Cookbook
Junos Cookbook (Cookbooks (OReilly))
ISBN: 0596100140
EAN: 2147483647
Year: 2007
Pages: 290
Authors: Aviva Garrett

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