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Loop prevention and advanced topics:


Adjancency Attributes

Unique Attributes

The following attributes must be unique for every node in the OSPF topology.

1. Router-ID: The router ID must be unique for every OSPF node. The router ID is either manually set or automatically set by using the highest active loopback IP followed by the highest active interface IP. If this is not unique, it can cause routers to start withdrawing each others routes and cause really weird routing issues.

2. Interface IP address: For OSPFv2, the IPv4 address must be unique on each link. For OSPFv3, the link-local must be unique.

Common Attributes

1. Interface Area ID: If one router's link is in area 1 and another is in area 2, they will not be able to form an adjacency as they are in different areas.

2. Hello and Dead Timers: Hello / Dead timers must match on both sides of the link.

3. Interface Network Address: Must be unique between neighbors

4. Interface MTU: A mismatch can cause issues with forming an adjacency or when the neighbors are exchanging database information.

5. Network Type:

6. Authentication:

7. Stub Flags:

8. Other Optional Capabilities:

Packet Types



  • Local Router-ID
  • Local Area-ID
  • to be continued