WAN Troubleshooting Knowledge Base Structure

Each page will include:

1. Troubleshooting methodology – the universal steps you always follow.

2. Checklists per protocol – what to check first, in order.

3. Golden commands – Cisco & Nokia side by side, for quick copying.

4. Reference configs – minimal working configs you can compare.

5. Common mistakes / pitfalls – what usually breaks and how to spot it.

6. Quick fix recipes – short instructions for the most common failures.

1. Troubleshooting Methodology

1. Verify physical connectivity: ping, traceroute, interface up.

   1. Check interfaces are UP / line protocol UP

      1. Cisco:

         • show ip interface brief

         • show interfaces Gig0/0

      2. Nokia:

         • show router interface

         • show port <port-id>

   2. Ping directly connected neighbbor

   3. Traceroute if multihop

2. Verify IGP basics: interface IPs, MTU, ACL, reachability.

   1. Check interface IPs

      1. Cisco: show running-config | section interface

      2. Nokia: show router interface

   2. Check MTU consistency

      1. Cisco: show interfaces Gig0/0 | include MTU

      2. Nokia: show router interface detail

   3. Check ACLs/firewall blocking OSPF (protocol 89)

      1. Cisco: show access-lists

      2. Nokia: show filter

3. Verify neighbor states: DOWN → INIT → EXSTART → LOADING → FULL.

   1. Show OSPF neighbors

      1. Cisco: show ip ospf neighbor

      2. Nokia: show router ospf neighbor

4. Verify area types: backbone, stub, NSSA, totally stubby.

   1. Cisco:

      1. show ip ospf (check area type backbone = 0)

      2. show running-config | section ospf

   2. Nokia:

      1. show router ospf area

      2. show router ospf

   3. Check both sides are in the same area type -- mismatches --> neighbors from but LSAs rejected

5. Verify LSAs: flooding, SPF, missing routes.

   1. View LSDB (OSPF Database)

      1. Cisco: show ip ospf database

      2. Nokia: show router ospf lsdb

   2. Check SPF runs (Cisco only)

      1. show ip ospf statistics (spf count should increase after topology changes)

6. Check authentication (plain or MD5).

   1. Cisco: show ip ospf interface Gig0/0 (check auth type + key ID)

   2. Nokia: show rotuer ospf interface

   3. Mismatch = adjancy stuck in DOWN or EXSTART

7. Compare running config vs reference config.

   1. Cisco: show running-config | section ospf

   2. Nokia: show router ospf

   3. Look for:

      1. Router IDs are unique

      2. Area IDs match

      3. Passive vs non Passive is correct

      4. Authentication keys identical

8. Use debug/logs carefully if needed.

   1. Cisco:

      1. debug ip ospf adj

      2. debug ip ospf hello

   2. Nokia:

      1. tools dump router ospf hello

      2. tools dump router ospf adj

   3. Use only in lab or during maintenance windows (HIGH CPU)

2. OSPF Checklist

• Neighbor stuck DOWN → check cabling, interface shutdown, ACLs

  • Cisco: show ip ospf neighbor

  • Cisco: show interfaces Gig0/0

  • Nokia: show router ospf neighbor

  • Nokia: show router interface

• Neighbor INIT → hello packets mismatch

  • Cisco: debug ip ospf hello

  • Cisco: show ip ospf interface Gig0/0 (check Hello/dead timers, network type)

  • Nokia: tools dump router ospf hello

  • Nokia: show router ospf interfaces

• Neighbor EXSTART/EXCHANGE → MTU mismatch, duplicate Router ID

  • Cisco: show interfaces Gig0/0 | include MTU

  • Cisco: show ip ospf (check ROUTER ID)

  • Nokia: show router interface detail

  • Nokia: show router ospf

• Neighbor LOADING → database mismatch

  • Cisco: show ip ospf database

  • Cisco: debug ip ospf adj

  • Nokia: show router ospf lsdb

  • Nokia: tools dump router ospf adj

• Routes missing → area misconfig, summarization, redistribution missing

  • Cisco: show ip route ospf

  • Cisco: show running-config | section ospf

  • Nokia: show router router-table protocol ospf

  • Nokia: show router ospf

• LSAs being rejected → authentication or area mismatch

  • Cisco: show ip ospf interface Gig0/0 (auth mismatch)

  • Cisco: debug ip ospf adj (will log auth failure)

  • Nokia: show router ospf interface (auth type/key)

  • Nokia: tools dump router ospf adj

5. Common Mistakes / Pitfalls

• MTU mismatch on WAN links → neighbor stuck in EXSTART

• Duplicate Router ID → neighbor never forms

• Passive interface on wrong link → neighbor stuck DOWN

• Area type mismatch → routes missing or LSAs rejected

• Redistributed routes missing → check route maps/policies

6. Quick Fix Recipes

• Neighbor stuck DOWN → ping neighbor, check ACL, interface status, clear ospf process

• Neighbor stuck EXSTART → check MTU, router IDs, interface type (broadcast vs point-to-point)

• Route missing → check area type, summarize, redistribution

• Authentication errors → check MD5 keys match