Technical Documentation

Configuring CSPF Tracing


When the output of the show mpls lsp extensive command indicates that the CSPF algorithm has failed, configuring CSPF tracing on the ingress router can often provide more information about the problem.


On the ingress router, to configure a log file and specify MPLS tracing flags, follow these steps:

  1. In configuration mode, go to the following hierarchy level:
    [edit]user@host# edit protocols mpls
  2. Configure a log file:
    [edit protocols mpls]user@host# set traceoptions file filename
  3. Depending on your situation, specify all or one of the following CSPF-specific tracing flags:
    [edit protocols mpls] user@host# set traceoptions flag cspf user@host# set traceoptions flag cspf-link user@host# set traceoptions flag cspf-node
  4. Verify and commit the configuration:
    user@host# show user@host# commit

Sample Output

[edit protocols mpls]
user@R1#  show 
traceoptions {
     file cspf;
    flag cspf;
    flag cspf-link;
    flag cspf-node;
label-switched-path R6-to-R1 {
interface so-0/0/0.0;
interface so-0/0/1.0;
interface so-0/0/2.0;
interface so-0/0/3.0;


The sample output shows a typical CSPF tracing configuration. The log file cpsf contains all the information gathered for each configured flag. Each flag provides slightly different information about CSPF computations. The cspf flag traces CSPF computations only; the cspf-link flag traces links visited during CSPF computations, and the cspf-node flag traces nodes visited during CSPF computations. See Examining the CSPF Log File for information about examining a CSPF log file.

Published: 2010-01-30