文档介绍：域间路由和BGP
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内容
Part I : 域间路由和BGP的基本概念
· 自治系统(域间路由的基本单元)
· 边界网关协议(BGP)
BGP 基本概念
BGP 路径属性
BGP 实现策略
Part II : BGP扩展能力
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自治路由域
由一个机构进行统一管理的网络和路由器的集合。
自治系统是一个分配有自治系统号码的自治路由域。
works
works
ISP works
…
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ASN
ASNs are 16 bit values.
64512 through 65535 are “private”
Genuity: 1
MIT: 3
Harvard: 11
UC San Diego: 7377
AT&T: 7018, 6341, 5074, …
: 701, 702, 284, 12199, …
Sprint: 1239, 1240, 6211, 6242, …
:AS4808,AS4809,AS4810…
ASNs represent units of routing policy
Currently over 11,000 in use.
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动态选路的体系结构
AS 1
AS 2
BGP
EGP = Exterior Gateway Protocol
IGP = Interior Gateway Protocol
基于参数: OSPF, IS-IS, RIP,
EIGRP (cisco)
基于策略: BGP
。
OSPF
EIGRP
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Link State
Vectoring
EGP
IGP
BGP
RIP
IS-IS
OSPF
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一台路由器可以支持多种路由协议
Forwarding Table
OSPF域
RIP域
BGP
OS kernel
OSPF Process
OSPF Routing tables
RIP Process
RIP Routing tables
BGP Process
BGP Routing tables
Forwarding Table Manager
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Non-transit vs. Transit AS
ISP 1
ISP 2
Non-transit AS
might be a corporate
or work.
Could be a “content
provider”
NET A
Traffic NEVER
flows from ISP 1
A to ISP 2
(At least not intentionally!)
IP traffic
Service
providers (often)
have transit
networks
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Selective Transit
NET B
NET C
NET A provides transit
B C
and D
C
NET A
NET D
NET A DOES NOT
provide transit
D
B
Most works transit in a selective manner…
IP traffic
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Customers and Providers
Customer pays provider for access to the
provider
customer
IP traffic
provider
customer
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