Overview Of Ospf; Link-State Database - Extreme Networks Summit Summit24 Installation And User Manual

Interior Gateway Routing Protocols
NOTE
If you are using RIP with supernetting/Classless Inter-Domain Routing (CIDR), you must use RIPv2
only. In addition, RIP route aggregation must be turned off.

Overview of OSPF

OSPF is a link-state protocol that distributes routing information between routers belonging to a single
IP domain, also known as an autonomous system (AS). In a link-state routing protocol, each router
maintains a database describing the topology of the autonomous system. Each participating router has
an identical database maintained from the perspective of that router.
From the link-state database (LSDB), each router constructs a tree of shortest paths, using itself as the
root. The shortest path tree provides the route to each destination in the autonomous system. When
several equal-cost routes to a destination exist, traffic can be distributed among them. The cost of a
route is described by a single metric.
NOTE
A Summit24e3 can support up to two non-passive OSPF interfaces, and cannot be a designated or a
backup designated router.

Link-State Database

Upon initialization, each router transmits a link-state advertisement (LSA) on each of its interfaces.
LSAs are collected by each router and entered into the LSDB of each router. Once all LSAs are received,
the router uses the LSDB to calculate the best routes for use in the IP routing table. OSPF uses flooding
to distribute LSAs between routers. Any change in routing information is sent to all of the routers in the
network. All routers within an area have the exact same LSDB. Table 54 describes LSA type numbers.
Table 54: LSA Type Numbers
Type Number Description
1 Router LSA
2 Network LSA
3 Summary LSA
4 AS summary LSA
5 AS external LSA
7 NSSA external LSA
9 Link local
10 Area scoping
11 AS scoping
186 Summit24e3 Switch Installation and User Guide