OSPF

OSPF Summary

The characteristics of OSPF follow:

Link-state routing protocol.

Uses IP protocol 89.

Classless protocol (supports VLSMs and CIDR).

Metric is cost, based on interface bandwidth by default (10^8 / BW in bps).

Sends partial route updates only when there are changes.

Send hello packets every 10 sec with dead timer of 40 sec over P-P & BC networks.

Send hello packets every 30 sec with dead timer of 120 sec over NBMA networks.

If the network is stable and there have been no updates within 30 min, a compressed update is sent.

Routes labeled as intra-area, interarea, external Type 1, or external Type 2.

Support for authentication.

Uses Dijkstra algorithm to calculate SPF tree.

Default administrative distance is 110.

Uses multicast address 224.0.0.5 (ALLSPFRouters).

Uses multicast address 224.0.0.6 (ALLDRouters).

Recommended for large networks.

For 2 routers to be adjacent :
1st. Hello packets must be sent & received.
2nd They must have the same hello & dead timers Also & same Net ID with subnet mask.
3rd They must be in the same area.

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