Weight is a cisco proprietary bgp metric. Default metric is
0 for external routes and 32768 for locally generated routes. Higher value is
preferred. Default configs are
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
int lo 2
ip add 150.150.151.1 255.255.255.0
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
network 150.150.150.0 mask 255.255.255.0
network 150.150.151.0 mask 255.255.255.0
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
network 77.77.77.0 mask 255.255.255.0
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
network 99.99.99.0 mask 255.255.255.0
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
network 200.200.200.0 mask 255.255.255.0
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
1) Ensure ISP2 prefers R3 to get out of its AS
Presently, ISP2’s routing table is
Network Next Hop Metric LocPrf Weight Path
* 77.77.77.0/24 40.40.40.1 0 100 i
*> 10.10.10.1 0 100 i
* 99.99.99.0/24 10.10.10.1 0 100 i
*> 40.40.40.1 0 0 100 i
*> 100.100.100.0/24 0.0.0.0 0 32768 i
*> 100.100.101.0/24 0.0.0.0 0 32768 i
*> 100.100.102.0/24 0.0.0.0 0 32768
i
*> 100.100.103.0/24 0.0.0.0 0 32768 i
* 150.150.150.0/24 40.40.40.1 0 100 i
*> 10.10.10.1 0 0 100 i
* 200.200.200.0 10.10.10.1 0 100 111 i
*> 40.40.40.1 0 100 111
i
We see that default weight is 0 for external routes and 32678 for local
routes
Recall that there
is no bgp default weight command, so we wld need a little tweaking
Isp2(conf)# ip as-path
access-list 1 permit .*
route-map
A permit 10
match
as-path 1
set weight 20
exit
router
bgp 222
nei 40.40.40.1 route-map A in
do
clear ip bgp * in
do
clear ip bgp * out
do
sh ip bgp
Network Next Hop Metric LocPrf Weight Path
*> 150.150.150.0/24 40.40.40.1 20 100 i
* 10.10.10.1 0 0
100 i
* 200.200.200.0 10.10.10.1 0 100
111 i
*> 40.40.40.1 20 100 111 i
2) remov d cfg and ensure isp2
prefers r3 to reach 99.99.99.1 and r1 to reach 150.150.150.1
Assuming the prefix-lists, route-maps have been removed
ISP2(conf)# ip prefix-list
o seq 5 permit 150.150.150.0/24
ip
prefix-list p seq 5 permit 99.99.99.0/24
route-map
o permit 10
match
ip address prefix-list o
set weight 30
route-map
o permit 20
exit
route-map
p permit 10
match ip address prefix-list p
set weight 20
route-map
p permit 20
exit
router
bgp 222
neighbor 10.10.10.1 route-map
o in
neighbor 40.40.40.1 route-map
p in
do
clear ip bgp * in
do
clear ip bgp * out
do
sh ip bgp
Network Next Hop Metric LocPrf Weight Path
* 150.150.150.0/24 40.40.40.1 0 100
i
*>
10.10.10.1 0 30 100 i
* 99.99.99.0/24 10.10.10.1 0 100
i
*> 40.40.40.1 0 20 100 i
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