Basic MPLS Troubleshooting Tips

1. Verifying MPLS Configuration:

• Cisco:
  • Use show mpls interfaces to verify that MPLS is enabled on the correct interfaces.
  • Check show mpls ldp neighbor to ensure that Label Distribution Protocol (LDP) neighbors are discovered, and that the session is up.
• Juniper:
  • Use show mpls interface to check MPLS status on interfaces.
  • Utilize show mpls ldp session to confirm LDP neighbor sessions.

2. Checking Label Switch Paths (LSP):

• Cisco:
  • Use show mpls ldp bindings to display local and remote label bindings.
  • show mpls forwarding-table helps to inspect the labels being forwarded and their corresponding next-hops.
• Juniper:
  • Use show mpls lsp extensive to get detailed information about the LSPs.
  • show route table mpls.0 to view the label-switched routes.

3. Ensuring Proper Route Distribution:

• Cisco:
  • Verify routing protocols are correctly redistributing routes with show ip route and show ip protocols.
  • Ensure that MPLS labels are being properly assigned by checking show mpls forwarding-table.
• Juniper:
  • Check routing information with show route forwarding-table family mpls.
  • Ensure correct route redistribution settings with show route protocol.

4. Troubleshooting MPLS VPNs:

• Cisco:
  • For issues with VRF (Virtual Routing and Forwarding), use show ip vrf and show ip route vrf [vrf-name].
  • Verify MPLS VPN label distribution and path information using show mpls forwarding-table vrf [vrf-name].
• Juniper:
  • Check VRFs using show route table [vrf-name].inet.0.
  • Look at the VPN labels with show route table [vrf-name].inet.0 detail.

5. Utilizing Cisco debug and Juniper traceoptions:

• Cisco:
  • In-depth troubleshooting can be performed by enabling debugging: debug mpls ldp for LDP-related issues or debug mpls traffic-eng for traffic engineering problems.
• Juniper:
  • Use traceoptions under the MPLS or routing protocol configuration to capture more detailed logs for troubleshooting.

6. Common Pitfalls and Checks:

• Both Cisco and Juniper:
  • Ensure there are no MTU mismatches across MPLS-enabled interfaces, as this can disrupt proper LSP formation.
  • Regularly check for software or firmware updates that address known bugs or add enhancements to MPLS features.