Why can i not establish the OSPF neighbor relationship over ATM or FR links


The possible cause of this is that the IP address of the neighboring router and designated router (DR) priority are not configured.

Other related questions:
Why can IS-IS neighbors not be established
This has the following possible causes: -Point-to-multipoint (P2MP) interfaces do not support the Intermediate System to Intermediate System routing protocol (IS-IS). -The MTU of the Ethernet Interface is smaller than the max-size of IS-IS LSP packets plus 3. -The MTU of the point-to-point (P2P) interface is less than the length of the IS-IS LSP packet. -The two ends have different parameter configurations.

Can OSPF establish a neighbor relationship by using the secondary IP address
In OSPF, a neighbor relationship cannot be established by using the secondary IP address; instead, a neighbor relationship can be established only by using the primary address of an interface. If the network to which the secondary IP address belongs is added to the OSPF configuration, however, the corresponding route can be advertised.

Can an OSPF neighbor relationship be established between devices that are on different subnets
A neighbor relationship can be established between two routers that are not on the same subnet only when the devices are connected through point-to-point (P2P) links. On a Point-to-Multipoint (P2MP) network, you can determine whether adjacencies can be formed between neighbors that are not on the same subnet. In all other cases, the devices must be on the same subnet.

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