This is a very cool feature cos it saves bandwidth. i.e. A
will tell B that it does not need a set of routes, so B does not need to send
it at all.
Default configs include ip address and bgp neighbor relationship
Default configs include ip address and bgp neighbor relationship
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 1.1.1.1 255.255.255.0
no shut
exit
ip route 22.22.22.0 255.255.255.0 s0/0
router eigrp 1
network 20.20.20.0 0.0.0.255
network 1.1.1.1 0.0.0.0
no auto-summary
exit
router bgp 100
nei 22.22.22.22 remote-as 222
nei 22.22.22.22 update-source lo 1
nei 22.22.22.22 ebgp-multihop 2
nei 2.2.2.2 remote-as 100
nei 2.2.2.2 update-source lo 1
nei 2.2.2.2 next-hop-self
nei 3.3.3.3 remote-as 100
nei 3.3.3.3 update-source lo 1
nei 3.3.3.3 next-hop-self
bgp router-id 1.1.1.1
no synchronization
r2
int s0/1
ip add 20.20.20.2 255.255.255.0
no shut
int s0/0
ip add 30.30.30.2 255.255.255.0
no shut
int s0/2
ip add 50.50.50.2 255.255.255.0
no shut
int lo 1
ip add 2.2.2.2 255.255.255.0
no shut
exit
ip route 11.11.11.0 255.255.255.0 s0/2
router eigrp 1
network 20.20.20.0 0.0.0.255
network 30.30.30.0 0.0.0.255
network 2.2.2.2 0.0.0.0
no auto-summary
exit
router bgp 100
nei 11.11.11.11 remote-as 111
nei 11.11.11.11 update-source lo 1
nei 11.11.11.11 ebgp-multihop 2
nei 1.1.1.1 remote-as 100
nei 1.1.1.1 update-source lo 1
nei 1.1.1.1 next-hop-self
nei 3.3.3.3 remote-as 100
nei 3.3.3.3 update-source lo 1
nei 3.3.3.3 next-hop-self
bgp router-id 2.2.2.2
no synchronization
r3
int s0/1
ip add 30.30.30.1 255.255.255.0
no shut
int s0/0
ip add 40.40.40.1 255.255.255.0
no shut
int lo 1
ip add 3.3.3.3 255.255.255.0
no shut
exit
ip route 22.22.22.0 255.255.255.0 s0/0
router eigrp 1
network 30.30.30.0 0.0.0.255
network 3.3.3.3 0.0.0.0
no auto-summary
exit
router bgp 100
nei 22.22.22.22 remote-as 222
nei 22.22.22.22 update-source lo 1
nei 22.22.22.22 ebgp-multihop 2
nei 2.2.2.2 remote-as 100
nei 2.2.2.2 update-source lo 1
nei 2.2.2.2 next-hop-self
nei 1.1.1.1 remote-as 100
nei 1.1.1.1 update-source lo 1
nei 1.1.1.1 next-hop-self
bgp router-id 3.3.3.3
no synchronization
ISP2
int s0/1
ip add 10.10.10.2 255.255.255.0
no shut
int s0/0
ip add 40.40.40.2 255.255.255.0
no shut
int lo 1
ip add 22.22.22.22 255.255.255.0
no shut
int lo 2
ip add 23.23.23.23 255.255.255.0
no shut
exit
ip route 1.1.1.0 255.255.255.0 s0/0
ip route 3.3.3.0 255.255.255.0 s0/1
router bgp 222
nei 1.1.1.1 remote-as 100
nei 1.1.1.1 update-source lo 1
nei 1.1.1.1 ebgp-multihop 2
nei 3.3.3.3 remote-as 100
nei 3.3.3.3 update-source lo 1
nei 3.3.3.3 ebgp-multihop 2
bgp router-id 22.22.22.22
no synchronization
ISP1
int
s0/0
ip add 50.50.50.1 255.255.255.0
no shut
int lo 1
ip add 11.11.11.11 255.255.255.255
no shut
int lo 2
ip add 12.12.12.12 255.255.255.0
no shut
exit
ip route 2.2.2.0 255.255.255.0 s0/0
router bgp 111
nei 2.2.2.2 remote-as 100
nei 2.2.2.2
update-source lo 1
nei 2.2.2.2
ebgp-multihop 2
bgp router-id 11.11.11.11
no synchronization
1) isp2 shld
advertise network 23.23.23.0/24 out but isp1 shld not rcv it.Configure routers
in such a way that changing the inbound filtering policy on ISP1 should force
R2 to apply the right filtering preventing it from sending prefixes ISP1 does
not wish to receive.
Lets confirm that ISP2 is advertising the route and also
confirm ISP1 is receiving it
ISP2#sh ip bgp
*>
23.23.23.0/24 0.0.0.0 0 32768 i
ISP1#sh ip bgp
Network Next Hop Metric LocPrf
Weight Path
*> 23.23.23.0/24 2.2.2.2
0 100 222 i
Now lets configure routers ISP1 and R2
ISP1(conf)#ip
prefix-list A seq 5 deny 23.23.23.0/24
ip prefix-list A
seq 10 permit 0.0.0.0/0 le 32
router bgp 111
nei 2.2.2.2 capability orf
prefix-list send [ISP1 sends to R2 the routes it
doesnot need]
nei 2.2.2.2 prefix-list A in
do clear ip bgp
2.2.2.2 in
do clear ip bgp
2.2.2.2 out
Going to R2, we need to tell it to accept the orf
prefix-list
R2(conf)#router bgp 100
nei 11.11.11.11 capability
orf prefix-list receive
do clear ip bgp
11.11.11.11 in
do clear ip bgp
11.11.11.11 out
Now lets prove that our config rocks
ISP1# sh ip
bgp nei 2.2.2.2
Outbound Route Filter (ORF)
type (128) Prefix-list:
Send-mode: advertised [advertised
means ISP1 is cfged for send-mode]
Receive-mode: received
Outbound Route Filter (ORF):
sent;
Incoming update prefix filter
list is A
R2# sh ip bgp
nei 11.11.11.11
Outbound Route Filter (ORF)
type (128) Prefix-list:
Send-mode: received
Receive-mode: advertised
Outbound Route Filter (ORF):
received (2 entries)
R2#sh ip bgp
nei 11.11.11.11 advertised-route
This displays empty route since ntwk 23.23.23.0 would not be sent to
11.11.11.11 bcos of the prefix-list
ISP1# sh ip
bgp
Network Next Hop Metric LocPrf Weight Path
*> 12.12.12.0/24
0.0.0.0 0 32768 i
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