I have been using prefix-list right from where I started
bgp. Now lets talk abt it
Default prefix-list seq no is 5 and it also follows the
implicit deny all
permit 0.0.0.0/1 le 8
permit 128.0.0.0/2 le 16
permit 192.0.0.0/3 le 24
Default config include bgp nei relationship and isp2 is advertising its
network to all routers in the domain
R1.....................
int s0/1
ip add 20.20.20.1 255.255.255.0
no shut
int s0/0
ip add 10.10.10.1 255.255.255.0
no shut
int lo 1
ip add 150.150.150.1 255.255.255.0
no shut
exit
router eigrp 1
network 20.20.20.0 0.0.0.255
network 10.10.10.0 0.0.0.255
no auto-summary
exit
router bgp 100
nei 10.10.10.2 remote-as 222
nei 20.20.20.2 remote-as 100
nei 20.20.20.2 next-hop-self
nei 30.30.30.1 remote-as 100
nei 30.30.30.1 next-hop-self
bgp router-id 150.150.150.1
no synchronization
R2..................
int s0/0
ip add 30.30.30.2 255.255.255.0
no shut
int s0/1
ip add 20.20.20.2 255.255.255.0
no shut
int s0/2
ip add 50.50.50.2 255.255.255.0
no shut
int lo 1
ip add 77.77.77.1 255.255.255.0
no shut
exit
router eigrp 1
network 20.20.20.0 0.0.0.255
network 30.30.30.0 0.0.0.255
network 50.50.50.0 0.0.0.255
no auto-summary
exit
router bgp 100
nei 30.30.30.1 remote-as 100
nei 30.30.30.1 next-hop-self
nei 20.20.20.1 remote-as 100
nei 20.20.20.1 next-hop-self
nei 50.50.50.1 remote-as 111
bgp router-id 77.77.77.1
no synchronization
R3..........................
int s0/0
ip add 40.40.40.1 255.255.255.0
no shut
int s0/1
ip add 30.30.30.1 255.255.255.0
no shut
int lo 1
ip add 99.99.99.1 255.255.255.0
no shut
exit
router eigrp 1
network 30.30.30.0 0.0.0.255
network 40.40.40.0 0.0.0.255
no auto-summary
router bgp 100
nei 40.40.40.2 remote-as 222
nei 30.30.30.2 remote-as 100
nei 30.30.30.2 next-hop-self
nei 20.20.20.1 remote-as 100
nei 20.20.20.1 next-hop-self
bgp router-id 99.99.99.1
no synchronization
ISP1..................................
int s0/0
ip add 50.50.50.1 255.255.255.0
no shut
int lo 1
ip add 200.200.200.1 255.255.255.0
no shut
exit
router bgp 111
nei 50.50.50.2 remote-as 100
bgp router-id 200.200.200.1
no synchronization
ISP2..................
int s0/1
ip add 40.40.40.2 255.255.255.0
no shut
int
s0/0
ip add 10.10.10.2 255.255.255.0
no shut
int lo 1
ip add 100.100.100.1 255.255.255.0
no shut
int lo 2
ip add 100.100.101.1 255.255.255.0
no shut
int lo 3
ip add 100.100.102.1 255.255.255.0
no shut
int lo 4
ip add 100.100.103.1 255.255.255.0
no shut
exit
router bgp 222
nei 10.10.10.1 remote-as 100
nei 40.40.40.1 remote-as 100
bgp router-id 100.100.100.1
no synchronization
network 100.100.100.0 mask 255.255.255.0
network 100.100.101.0 mask 255.255.255.0
network 100.100.102.0 mask 255.255.255.0
network 100.100.103.0 mask 255.255.255.0
Task 1) ISP1 should filter out prefixes 100.x.x.x.Use a sequence
no of 10. Use prefix-list
Lets prove that ISP1 is getting the routes
ISP1# sh ip bgp
Network Next Hop Metric LocPrf Weight Path
*> 100.100.100.0/24 50.50.50.2 0 100 222 i
*> 100.100.101.0/24 50.50.50.2 0 100 222 i
*> 100.100.102.0/24 50.50.50.2 0 100 222 i
*> 100.100.103.0/24 50.50.50.2 0 100 222 i
ISP(conf)# ip
prefix-list A seq 10 deny 100.100.0.0/16 ge 24 le 24
ip prefix-list seq 20 permit 0.0.0.0/0 le 32
router bgp 111
nei 50.50.50.2 prefix-list A in
do clear ip bgp 50.50.50.2 in
do clear ip bgp 50.50.50.2 out
To view the changes made,
ISP1#sh
ip bgp [we
see no routes]
ISP1#sh
ip bgp nei 50.50.50.2 routes [w see no routes]
ISP1#sh
ip bgp nei 50.50.50.2 received-route [to
display routes rcved from nei but not accepted]
Network Next Hop Metric LocPrf Weight Path
* 100.100.100.0/24
50.50.50.2 0 100 222 i
* 100.100.101.0/24
50.50.50.2 0 100 222 i
* 100.100.102.0/24
50.50.50.2 0 100 222 i
* 100.100.103.0/24
50.50.50.2 0
100 222 i
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