Must two S series switches be on the same network segment to set up an OSPF neighbor relationship

Question: Must the interfaces on two ends of an OSPF link be on the same network segment and the mask digits on the neighboring interfaces be consistent?

Answer: When two S series switches are establishing an OSPF neighbor relationship, the interfaces on the broadcast network, NBMA network, or P2MP network must be on the same network segment and the mask digits on the neighboring interfaces must be consistent. The limitations do not apply to interfaces on a P2P network. On an OSPF P2P network, if the link-layer protocol is PPP, OSPF neighbors with IP addresses on different network segments can be in the Full state and correctly calculate routes. However, if the link-layer protocol is not PPP (for example, HDLC), devices with IP addresses on different network segments cannot establish an OSPF neighbor relationship. Through PPP negotiation, the local device can obtain the IP address of the remote device and have a route to the remote device without extra configuration.

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