Hello everyone,
This is my first post in this community. I have read everywhere that outbound BGP path is easy to manipulate than inbound BGP path but in may case ( must be my lack of knowledge) I am having difficulties selecting proper outbound path and this is resulting in asymmetric routing. I am looking forward for knowledge and a solution for my problem here.
I have /22 provider independent network and three upstream provider ISPs with separate physical connection.
I am using 7200 series router and below is my sample config (I have changed IP addresses and AS number ):
router bgp 100
no synchronization
no bgp enforce-first-as
bgp log-neighbor-changes
network 10.10.1.0 mask 255.255.252.0
network 10.10.1.0 mask 255.255.254.0
network 10.10.1.0
network 10.10.2.0
network 10.10.3.0 mask 255.255.254.0
network 10.10.3.0
network 10.10.4.0
neighbor 192.168.1.1 remote-as 11
neighbor 192.168.1.1 description A
neighbor 192.168.1.1 next-hop-self
neighbor 192.168.1.1 soft-reconfiguration inbound
neighbor 192.168.1.1 route-map rm_A_in in
neighbor 192.168.1.1 route-map rm_A_out out
neighbor 192.168.2.1 remote-as 12
neighbor 192.168.2.1 description B
neighbor 192.168.2.1 next-hop-self
neighbor 192.168.2.1 soft-reconfiguration inbound
neighbor 192.168.2.1 route-map rm_B_in in
neighbor 192.168.2.1 route-map rm_B_out out
neighbor 192.168.3.1 remote-as 13
neighbor 192.168.3.1 description C
neighbor 192.168.3.1 next-hop-self
neighbor 192.168.3.1 soft-reconfiguration inbound
neighbor 192.168.3.1 route-map rm_C_in in
neighbor 192.168.3.1 route-map rm_C_out out
no auto-summary
ip classless
ip route 10.10.1.0 255.255.252.0 172.16.1.2
ip route 10.10.1.0 255.255.254.0 172.16.1.2
ip route 10.10.1.0 255.255.255.0 172.16.1.2
ip route 10.10.2.0 255.255.255.0 172.16.1.2
ip route 10.10.3.0 255.255.254.0 172.16.1.2
ip route 10.10.3.0 255.255.255.0 172.16.1.2
ip route 10.10.4.0 255.255.255.0 172.16.1.2
ip prefix-list pl_BOGUS_in seq 5 deny 10.0.0.0/8
ip prefix-list pl_BOGUS_in seq 10 deny 172.16.0.0/12
ip prefix-list pl_BOGUS_in seq 15 deny 192.168.0.0/16
ip prefix-list pl_BOGUS_in seq 20 deny 169.254.0.0/16
ip prefix-list pl_BOGUS_in seq 25 deny 0.0.0.0/8
ip prefix-list pl_BOGUS_in seq 30 deny 127.0.0.0/8
ip prefix-list pl_BOGUS_in seq 35 deny 198.18.0.0/15
ip prefix-list pl_BOGUS_in seq 40 deny 192.0.2.0/24
ip prefix-list pl_BOGUS_in seq 45 deny 198.51.100.0/24
ip prefix-list pl_BOGUS_in seq 50 deny 203.0.113.0/24
ip prefix-list pl_BOGUS_in seq 55 permit 0.0.0.0/0 le 32
!
ip prefix-list pl_A_out seq 5 permit 10.10.3.0/24
ip prefix-list pl_A_out seq 10 permit 10.10.1.0/23
ip prefix-list pl_A_out seq 15 permit 10.10.3.0/23
ip prefix-list pl_A_out seq 25 deny 0.0.0.0/0 le 32
ip prefix-list pl_B_out seq 5 permit 10.10.1.0/24
ip prefix-list pl_B_out seq 10 permit 10.10.2.0/24
ip prefix-list pl_B_out seq 15 permit 10.10.3.0/23
ip prefix-list pl_B_out seq 25 deny 0.0.0.0/0 le 32
ip prefix-list pl_C_out seq 5 permit 10.10.4.0/24
ip prefix-list pl_C_out seq 10 permit 10.10.1.0/23
ip prefix-list pl_C_out seq 15 permit 10.10.3.0/23
ip prefix-list pl_C_out seq 25 deny 0.0.0.0/0 le
route-map rm_A_in permit 5
match ip address prefix-list pl_BOGUS_in
route-map rm_A_out permit 5
match ip address prefix-list pl_A_out
route-map rm_B_in permit 5
match ip address prefix-list pl_BOGUS_in
route-map rm_B_out permit 5
match ip address prefix-list pl_B_out
route-map rm_C_in permit 5
match ip address prefix-list pl_BOGUS_in
route-map rm_C_out permit 5
match ip address prefix-list pl_C_out
I am getting the desired result for inbound traffic, ie
Traffic from internet for 10.10.1.0/24 and 10.10.2.0/24 are coming via ISP A
Traffic from internet for10.10.3.0/24 are coming via ISP B
Traffic from internet for10.10.4.0/24 are coming via ISP C
But the problem is all traffic from My ASN to internet is going via single ISP (ISP B). If i change the weight or local-preference it will select another single ISP. This is causing the asymmetric routing.
Is their any way so that I can achieve symmetric traffic flow, ie:
Traffic from 10.10.1.0/24 and 10.10.2.0/24 to internet leave through ISP A
Traffic from 10.10.3.0/24 to internet leave through ISP A
Traffic from 10.10.4.0/24 to internet leave through ISP A
Any help will be highly appreciated. Thanks in advance.
