IP网络技术基础-路由协议详解

IP Header
Protocol Number
Packet Payload
TCP Header
Port No.
Segment Payload
C R C
BGP is an advanced distance vector routing protocol
• Relies on TCP for reliable session management
• Designed to scale to huge internetworks (for example, the Internet)
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BGP in IP Packets
6—TCP 17— UDP Frame Header
Frame Payload
179—BGP 23— Telnet 25— SMTP
• Uses TCP port number 179
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Tables
IGP Routing Protocol
BGP Routing Protocol
IP
BGP
• BGP has its own table, in addition to the IP routing table
• Information can be exchanged between the two tables
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Drawbacks to Link-State Routing Protocols
• Initial discovery may cause flooding. • Memory- and processor-intensive.
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距离矢量VS链路状态
距离矢量路由协议： share information locally
路由协议基础
内容
路由协议基本介绍
静态路由协议及 动态路由协议 路由协议nter + network
路由器( router ):
路由协议 :
route + er
routing protocol
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概念
地址 AS
： 10.10.10.10 /24 ： Autonomous system
路由表： 10.10.10.0/24 via 10.10.9.1
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What Is Routing?
To route, a router needs to do the following: • Know the destination address • Identify the sources it can learn from • Discover possible routes • Select the best route • Maintain and verify routing information
use a distributed route calculation
链路状态路由协议: information distributed unchanged ;
each router perform a local best-path calculation
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BGP协议
Border Gateway Protocol 广泛应用于目前Internet上 路径矢量 IBGP ，EBGP 路由对等体 策略
• Neighbors should be directly connected
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Policy-Based Routing
• BGP allows administrators to define policies, or rules, for how data will flow through the autonomous systems
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Peers = Neighbors
Neighbors
AS 65500
B C
Neighbors A
AS 65000
• Any two routers that have formed a TCP connection in order to exchange BGP routing information are called peers or neighbors
所有路由器会通过一种被称 为刷新（ Flooding ）的方法 来交换链路状态数据。
路由协议收敛以后，所有的 路由器会根据其各自的链路 状态信息数据库计算出各自 的路由表。
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相关内容
SPF算法 层次结构 Metric
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典型协议
OSPF IS-IS
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Link-State Routing Protocols
BGP
B
C
AS 64520
A
BGP AS 65250
F
AS 65500
BGP
D
E
• BGP is used between autonomous systems • Guarantees exchange of loop-free routing information
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BGP Characteristics
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Static Routes
• Configure unidirectional static routes to and from a stub network to allow communications to occur.
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Static Route Example
• This is a unidirectional route. You must have a route configured in the opposite direction.
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What Is Routing? (Cont.)
• Routers must learn destinations that are not directly connected.
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路由
Static Default Dynamic （1） 信息的传播 （2） 路由的计算
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Identifying Static and Dynamic Routes
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External BGP
IBGP Neighbors
AS 65500
B C
EBGP Neighbors
A
AS 65000
• When BGP neighbors belong to different autonomous systems it is called external BGP (EBGP)
Static Route
• Uses a route that a network administrator enters into the router manually
Dynamic Route
• Uses a route that a network routing protocol adjusts automatically for topology or traffic changes
BGP is a distance vector protocol with enhancements:
• Reliable updates—BGP runs on top of TCP (port 179) • Incremental, triggered updates only • Periodic keepalives to verify TCP connectivity • Rich metrics (called path vectors or attributes)
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BGP Attributes
BGP attributes include:
• AS-path
• Next-hop • Local preference • Multi-exit discriminator (MED) • Origin
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Autonomous Systems
IGPs: RIP, IGRP, OSPF, EIGRP EGPs: BGP
Autonomous System 65000 Autonomous System 65500 • An autonomous system (AS) is a collection of networks under a single technical administration
按作用原理分:
距离矢量: distance vector 链路状态: link - state
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Autonomous Systems: Interior or Exterior Routing Protocols
• An autonomous system is a collection of networks under a common administrative domain. • IGPs operate within an autonomous system.
• IGPs operate within an autonomous system • EGPs connect different autonomous systems
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BGP Is Used Between Autonomous Systems
• Routing Table Prefixes AS 020501 104,027B 65000
After initial flood, pass small event-triggered link-state updates to all other routers
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Link-State Network Hierarchy Example