OSPF Authentication Mismatch Troubleshooting

Detection

Check Authentication Type

R1# show ip ospf interface gi0/0 | include auth
  Message digest authentication enabled

R2# show ip ospf interface gi0/0 | include auth
  Simple password authentication enabled  ← MISMATCH!

Debug Output

R1# debug ip ospf adj
*OSPF-1 ADJ: Mismatch Authentication type. Input packet specified type 1, we use type 2

Fix: Match Authentication Type

Both routers use MD5:

R2(config)# interface gi0/0
R2(config-if)# ip ospf authentication message-digest
R2(config-if)# ip ospf message-digest-key 1 md5 SecurePassword

Fix: Match Passwords

Check configured password (hidden):

R1# show run interface gi0/0 | include key
 ip ospf message-digest-key 1 md5 7 060506324F41

Set matching password on R2:

R2(config-if)# ip ospf message-digest-key 1 md5 SecurePassword

Summary

✅ Match auth type — Both plain text or both MD5
✅ Match passwords — Exact same password
✅ Match key IDs — Same key ID number

Next: Routes Not Appearing (Article 23)

Internal Links:

• ← Area Mismatch (Article 19)
• ← OSPF Authentication (Article 13)
• ← Neighbors Not Forming (Article 18)