第5讲 第10章 路由协议-dk-好要点

Convergence time（收敛时间）
A measure of how quickly to recover from network changes
从不一致到一致所经历的时间
体现路由算法的效率
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Convergence（收敛）
Range: 1~65535（Private AS number: 64512~65535）
Internet由若干AS互相连接构成
核心主干网
每个AS内可能有多个网络存在 核心主干网也可以构成一个AS
核心主干网提供到所有可能的目的地的
AS
2 AS 1
AS 3
可靠的、统一的、权威的路由
ASx
ASy
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Metric（度量）
Metric：用来衡量通过某一网络所需的代价
代价是什么？
度量取决于所需
代价的度量取决于Routing Protocol
要的服务类型
Hop count（跳数）, bandwidth（带宽）, delay（延 迟）, MTU, load（负载）, reliability（可靠性）, …
To calculate the routing table based on the topology or the policies（策略）
Routing Table
Convergence
Static route manually define Dynamic route routing protocol
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Types of Autonomous Systems
Single-homed AS（残桩AS）
Only one exit point to the outside
Example: AS 1, AS 3
数据通信量不能通过残桩AS
域内路由和域间路由
为什么需要AS？
主要原因：Internet网络太大，一种路由协议无法更新所有路由器的路 由表
AS number
An identifying number that is assigned by an Internet registry or a service provide
links A router’s load Traffic patterns in relation to the topology
change
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Interior & Exterior Routing
Autonomous system（自治系统，AS）
A 64K
C 10M
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64K
Net
D
Hop count: A B Net Bandwidth: A C D源自文库 Net
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Convergence（收敛）
D
Convergence
A
B
C
Des t.
All routers in a network agree on the topology
路由器 一个路由器连接多个网络，当路由器收到
分组，应该将分组转发到哪个网络？
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Introduction
路由选择协议(Routing protocol)——使得路由器能够找 到到达目的地的最佳路径
To share the knowledge about the internet
AS 1 R
Multi-homed AS
More than one exit point to the outside
Example: AS 2
Nontransit AS——例如：大型公司网络
not allow transit traffic to pass through it
Transit AS（转接AS）
Table-driven routing（表驱动路由选择）
Overhead Scalability
One router More routed protocols
One routed protocol（例如IP） One routing table
One routed protocol More routing protocols
Routing protocol 使用Metric来选择一条 best path （最优路）for routing
The metric of a route = MIN{nS∈UPMath(Metricn)}
The metric of a route ＝ MAX{nM∈IPNath(Metricn)}
A group of networks and routers under the authority of a single administration
Each AS typically represents an independent organization and applies its own unique routing and security policies
Chapter 11 Routing Protocols
Interior(内部) and exterior(外部) routing
RIP OSPF BGP-4
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Introduction
互联网由许多路由器连接起来的网络组成 数据从源站点到目的站点，可能经过多个
Factors affecting convergence
The routing protocol used A router’s distance from the point of change The number of routers in the network Bandwidth and traffic load on communications