SW Version 2.04 30-January-2009 Page 92 of 128
Source net: The source network segment to be used as the source
IP address.
OSPF Area: Specified designated OSPF area.
RP Point: Rendezvous Point
MD5 Key ID: Secret keyword version
MD5 Key: Secret keyword
4.7.5.5 Defining the OSPF Area
One of the most important features of OSPF is the concept of an Area. An OSPF
network can be broken up into areas that are connected by Area Border Routers
(ABR). Routing information can then be summarized at the ABR before being passed
along to the next area. This means that routers in one area don't need to worry about
the LSA information from routers in other areas, which drastically improves network
stability and convergence times, as well as reducing the amount of resources required
to support OSPF on the routers.
For OSPF to work well, you need to allocate your IP addresses appropriately among
the Areas. In particular, you want to be able to summarize the routes for an Area
when you pass this information along to the next Area. The summarization doesn't
need to reduce perfectly to a single route for each Area. But the fewer LSAs you need
to pass between Areas, the better OSPF will scale.
Each Area has a 32-bit identifier number, which is often represented in dotted decimal
notation, similar to IP addresses. Every OSPF network should have an Area 0 (or
0.0.0.0), and every ABR must be a member of Area 0. This enforces a hierarchical
design model for OSPF networks. The one exception to this rule happens in a network
with only one Area. In this case, you can actually give this Area any number, we
recommend using an Area 0.
4.7.5.6 Defining the RP Point
In IGMP-v2 networks you will have to enable PIM and set a RP Point, disable PIM on
networks using IGMP-v3.
An RP is a router somewhere in the network that acts as a central distribution point
for one or more multicast groups. When the last-hop router receives an IGMP-v2
message from a device asking to join a group, it has to go looking for that group. The
best place to start looking is the RP.
4.7.5.7 MD5 Authentication
You may want to authenticate your OSPF neighbor relationships to ensure that no
unauthorized equipment is allowed to affect routing.
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