Troubleshooting OSPF Adjacency on Ethernet Segment

AB

OSPF (Open Shortest Path First) is a link-state routing protocol that works by creating a complete topology map of the network. To establish OSPF adjacency between routers, the following conditions must be met:

• The routers must have a common subnet.
• The hello and dead timers must match on both routers.
• The OSPF interface priorities must match.
• The OSPF area IDs must match.
• The OSPF network types must match.

In the scenario given, the adjacency is not coming up on an Ethernet segment. Here are two reasons that could cause this situation:

1. Mismatched IP subnet/mask: If the IP subnet/mask configured on one router is different from that configured on the other router, the OSPF adjacency will not come up. This is because OSPF relies on the routers having a common subnet to establish adjacency. If the subnets do not match, the routers will not be able to communicate with each other.

2. Hello timer intervals are mismatched: OSPF uses hello packets to discover and establish adjacency with neighboring routers. The hello packets contain information such as the router ID, area ID, and OSPF version number. The hello timer specifies the interval at which these packets are sent. If the hello timer intervals on one router are different from those on the other router, the OSPF adjacency will not come up. This is because the routers will not be able to establish communication if their hello packets are not synchronized.

Options C and D are not the correct answers for this scenario as they are not related to establishing adjacency on an Ethernet segment. Using different Junos versions on each side or having different OSPF priority values will not affect the adjacency on an Ethernet segment.