Lab 6-2 Using the AS_PATH Attribute

Topology

GNS檔案

SanJose
!
!Step 0: Basic Setting
conf t
hostname SanJose
no ip domain-lookup
end
!
!Step 1: IP Addressing
conf t
int s 0/0
ip add 192.168.1.5 255.255.255.252
no sh
int lo 0
ip add 201.0.0.1 255.255.255.0
no sh
end
!
!Step 2: Configure BGP
conf t
router bgp 100
neighbor 192.168.1.6 remote-as 300
network 201.0.0.0
end

ISP
!
!Step 0: Basic Setting
conf t
hostname ISP
no ip domain-lookup
end
!
!Step 1: IP Addressing
conf t
int s 0/0
ip add 192.168.1.6 255.255.255.252
no sh
int s 0/1
ip add 172.24.1.17 255.255.255.252
no sh
int lo 0
ip add 202.0.0.1 255.255.255.0
no sh
end
!
!Step 2: Configure BGP
conf t
router bgp 300
neighbor 192.168.1.5 remote-as 100
neighbor 172.24.1.18 remote-as 65000
network 202.0.0.0
end
!
!Step 3: Remove the Private AS
conf t
router bgp 300
neighbor 192.168.1.5 remove-private-as
end
!
!Step 4: Use the AS_PATH Attribute to Filter Routes
conf t
!過濾AS-Path字元為 開始100結束
ip as-path access-list 1 deny ^100$
!允許AS-Path字元為 一個字元+任意字元 = i 或 i xxx
ip as-path access-list 1 permit .*
end
!將產生好的as-path acl 套用到往172.24.1.18的更新上(OUT)
conf t
router bgp 300
neighbor 172.24.1.18 filter-list 1 out
end

CustRtr
!
!Step 0: Basic Setting
conf t
hostname CustRtr
no ip domain-lookup
end
!
!Step 1: IP Addressing
conf t
int s 0/1
ip add 172.24.1.18 255.255.255.252
no sh
int lo 0
ip add 203.0.0.1 255.255.255.0
no sh
!
!Step 2: Configure BGP
conf t
router bgp 65000
neighbor 172.24.1.17 remote-as 300
network 203.0.0.0
end

show指令
show ip route
show ip bgp
show ip bgp neighbor
show ip bgp regexp ^100$

clear指令
clear ip bgp *
clear ip bgp 192.168.1.5 soft out
clear ip bgp 172.24.1.18 soft out

參考文件
Removing Private Autonomous System Numbers in BGP

Using Regular Expressions in BGP