Extreme Networks ExtremeWare XOS 11.1, Руководство пользователя

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Interior Gateway Protocols
ExtremeWare XOS 11.1 Concepts Guide
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RIP Versus OSPF
The distinction between RIP and OSPF lies in the fundamental differences between distance-vector
protocols and link-state protocols. Using a distance-vector protocol, each router creates a unique routing
table from summarized information obtained from neighboring routers. Using a link-state protocol,
every router maintains an identical routing table created from information obtained from all routers in
the autonomous system (AS). Each router builds a shortest path tree, using itself as the root. The link-
state protocol ensures that updates sent to neighboring routers are acknowledged by the neighbors,
verifying that all routers have a consistent network map.
Advantages of RIP and OSPF
The biggest advantage of using RIP is that it is relatively simple to understand and to implement, and it
has been the
de facto routing standard for many years.
RIP has a number of limitations that can cause problems in large networks, including the following:
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A limit of 15 hops between the source and destination networks.
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A large amount of bandwidth taken up by periodic broadcasts of the entire routing table.
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Slow convergence.
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Routing decisions based on hop count; no concept of link costs or delay.
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Flat networks; no concept of areas or boundaries.
OSPF offers many advantages over RIP, including the following:
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No limitation on hop count.
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Route updates multicast only when changes occur.
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Faster convergence.
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Support for load balancing to multiple routers based on the actual cost of the link.
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Support for hierarchical topologies where the network is divided into areas.
The details of RIP and OSPF are explained later in this chapter.
Overview of RIP
RIP is an IGP first used in computer routing in the Advanced Research Projects Agency Network
(ARPAnet) as early as 1969. It is primarily intended for use in homogeneous networks of moderate size.
To determine the best path to a distant network, a router using RIP always selects the path that has the
least number of hops. Each router that data must traverse is considered to be one hop.
Routing Table
The routing table in a router using RIP contains an entry for every known destination network. Each
routing table entry contains the following information:
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IP address of the destination network
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Metric (hop count) to the destination network