3com 10014299 Betriebsanweisung

This chapter covers the following topics:

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Open Shortest Path First (OSPF) is an autonomous, link-state-based internal 
routing protocol developed by Internet Engineering Task Force (IETF). The current 
version is version 2 (RFC1583), which features the following: 

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Applicable range — Supports networks of various sizes and hundreds of 
routers.

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Fast convergence — Sends an update message immediately after the 
topological structure of the network is changed, so the change can be 
synchronized in the autonomous system.

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No self-loop — OSPF calculates the route with the shortest path tree algorithm 
through the collected link status. This algorithm ensures that no self-loop route 
is generated.

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Area division — An AS network can be divided into areas and the routing 
information between the areas is further abstracted, reducing the bandwidth 
occupation in the network.

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Equivalent route ----support multiple equivalent routes to the same destination 
address.

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Route level --- the four levels of routes according to different priorities: 
intra-area routes, inter-area routes, external route class 1 and external route 
class 2.

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Authentication ---- support interface-based message authentication to ensure 
the security of the route computation.

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Multicast ---packets are transmitted and received with multicast address on 
multicasting link layer, greatly reducing interference to other netw ork devices.

The entire network is composed of multiple autonomous systems (AS). The link 
state of an AS is collected and transmitted to determine and propagate the route 
dynamically and then synchronize the information of the AS. Each system is 
divided into areas. If a router port is allocated to multiple areas, it is an area 
boundary router (ABR) since it is located at the boundary and connected with 
multiple areas. Routing information of another area can be learned from the ABR. 
All ABRs and the routers between them form a backbone area, tagged with