To determine whether a possible Layer 1 or Layer 2 problem exists with a connection, display the
status of an interface using the show ip ospf neighbor command. ???Administratively Down???
indicates that the interface is not enabled. If the status of the interface is not up/up, there will be
no OSPF neighbor adjacencies. In Example 4-13, serial 0/0/1 is up/up.
Example 4-12 Verifying OSPF Neighbor State
RouterX#sshhooww iipp oossppff nneeiigghhbboorr
Neighbor ID Pri State Dead Time Address Interface
172.16.31.100 0 Full/ - 00:00:31 10.140.1.1 Serial0/0/0
192.168.1.81 0 Full/ - 00:00:31 10.23.23.2 Serial0/0/1
Troubleshoot
OSPF Neighbor
Adjacencies
Troubleshoot
OSPF Routing
Table Issues
Troubleshoot
OSPF
Authentication
Are all
interface statuses
up/up?
Do local and
neighbor MTU
sizes match?
Are all
required OSPF
neighbors
configured?
Does
all required
hello packet
information match
neighbor?
162 Chapter 4: Single-Area OSPF Implementation
For OSPF to create an adjacency with a directly connected neighbor router, both routers must
agree on the maximum transmission unit (MTU) size. To check the MTU size of an interface, use
the show interface command.
Pages:
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255