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Overview:
In this example, we want to stop routes that originated in AS1 from being advertised to AS3. We are going to do this in AS2.
Our Diagram:
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CHANGE AS-PATH INFORMATION ON R5
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R5 config:
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router bgp 2
no synchronization
bgp router-id 5.5.5.5
network 5.5.5.5 mask 255.255.255.255
network 10.1.4.0 mask 255.255.255.0
network 10.1.5.0 mask 255.255.255.0
network 10.1.6.0 mask 255.255.255.0
neighbor 3.3.3.3 remote-as 1
neighbor 3.3.3.3 ebgp-multihop 255
neighbor 3.3.3.3 update-source Loopback0
neighbor 4.4.4.4 remote-as 2
neighbor 4.4.4.4 ebgp-multihop 255
neighbor 4.4.4.4 update-source Loopback0
neighbor 4.4.4.4 route-reflector-client
neighbor 4.4.4.4 next-hop-self
neighbor 6.6.6.6 remote-as 3
neighbor 6.6.6.6 ebgp-multihop 255
neighbor 6.6.6.6 update-source Loopback0
neighbor 6.6.6.6 filter-list 5 out <====== Filter applied to neighbor
no auto-summary
!
no ip http server
ip classless
ip route 3.3.3.3 255.255.255.255 10.1.4.1
ip route 4.4.4.4 255.255.255.255 10.1.5.1
ip route 6.6.6.6 255.255.255.255 10.1.6.2
ip as-path access-list 5 deny ^1$ <====== Deny all routes starting in AS 1
ip as-path access-list 5 permit .* <====== Permit all other routes
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R6 output
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r6#sh ip bgp
BGP table version is 28, local router ID is 6.6.6.6
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*> 4.4.4.4/32 5.5.5.5 0 2 i
*> 5.5.5.5/32 5.5.5.5 0 0 2 i
*> 6.6.6.6/32 0.0.0.0 0 32768 i
*> 10.1.2.0/24 5.5.5.5 0 2 i
*> 10.1.4.0/24 5.5.5.5 0 0 2 i
*> 10.1.5.0/24 5.5.5.5 0 0 2 i
* 10.1.6.0/24 5.5.5.5 0 0 2 i
*> 0.0.0.0 0 32768 i
r6#
Routes from as1 missing like 1.1.1.1
r6#ping 1.1.1.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 1.1.1.1, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
r6#
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