User guide

E
XTREME
W
ARE
S
OFTWARE
U
SER
G
UIDE
12-5
O
VERVIEW OF
OSPF
RIP V
ERSION
1 V
ERSUS
RIP V
ERSION
2
A new version of RIP, called RIP version 2, expands the functionality of RIP version 1 to
include the following:
• 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.
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.
O
VERVIEW 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.
L
INK
-S
TATE
D
ATABASE
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.
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. Tab le 12-1 describes LSA type numbers.