Extreme Networks ExtremeWare XOS 10.1, Manual

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188 ExtremeWare XOS 10.1 Concepts Guide
Interior Gateway Protocols
RIP Version 1 Versus RIP Version 2
A new version of RIP, called RIP version 2, expands the functionality of RIP version 1 to include:
•
Variable-Length Subnet Masks (VLSMs).
• Support for next-hop addresses, which allows for optimization of routes in certain environments.
•
Multicasting.
RIP version 2 packets can be multicast instead of being broadcast, reducing the load on hosts that do
not support routing protocols.
NOTE
If you are using RIP with supernetting/Classless Inter-Domain Routing (CIDR), you must use RIPv2
only.
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.
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 36 describes LSA type numbers.
Table 36: 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—Opaque
10 Area scoping—Opaque
11 AS scoping—Opaque