TCP/IP 详解卷1 ch10 Dynamic Routing Protocols

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本文详细介绍了三种主要的路由协议：RIP、OSPF和BGP。RIP是一种距离矢量协议，使用UDP进行传输，存在收敛慢等问题；OSPF为链路状态协议，直接使用IP协议，具备多种优势如支持负载均衡及子网划分等；BGP则采用TCP作为传输协议，适用于边界网关。同时，文中还提及了CIDR技术以解决互联网路由表膨胀的问题。

1. RIP (Routing Information Protocol) - a distance-vector protocol

use UDP, port is 520, the metric is hop counts (The hop count for all directly connected interfaces is 1, max value is 15).

2. problems

1) RIP has no knowledge of subnet addressing

2) RIP takes a long time to stabilize after the failure of a router or a link

3) dest ip is 255.255.255.255, 全网广播

3. RIP-2 supports multicasting in addition to broadcasting

4. OSPF (Open Shortest Path First) - a link-state protocol

OSPF uses IP directly, it does not use UDP or TCP. OSPF has its own value for the protocol field in the IP header.

5. advantage of OSPF

1) OSPF can calculate a separate set of routes for each IP type-of-service

2) Each interface is assigned a dimensionless cost.

3) When several equal-cost routes to a destination exist, OSPF distributes traffic equally among the routes. This is called load balancing.

4) OSPF supports subnets: a subnet mask is associated with each advertised route.

5) Point-to-point links between routers do not need an IP address at each end.

6) A simple authentication scheme can be used.

7) OSPF uses multicasting, instead of broadcasting.

6. BGP (Border Gateway Protocol)

BGP uses TCP as its transport protocol

7. CIDR (Classless Interdomain Routing)

Although the allocation of these class C addresses solves one problem (running out of class B addresses) it introduces another problem: every class C network requires a routing table entry. Classless Interdomain Routing (CIDR) is a way to prevent this explosion in the size of the Internet routing tables.