ISP BGP High Availability / Failover

[okoroji80]

Hello Community Members,

How best can i connect my Router to two ISP links with BGP configured.

I in addition would like to do setup High availability on both links such that if ISP --A links becomes unstable due to constant flapping then  the Second ISP---B  takes over .

Thanks

[Georg Pauwen]

Hello,

flapping can be countered with BGP dampening.

As with regard to high availability, the options are numerous, and depend on your physical setup. If you provide more details (e.g. a schematic drawing of your setup), we can give you more details. In the meantime, have a look at the link below:

http://showipbgp.com/bgp-configurations/cisco.html

[okoroji80]

Attached Herewith is the sketch.

thanks

[Georg Pauwen]

Hello,

here is what the configuration would look like. In your setup, you can only do load sharing. I assumed your AS to be 10, and the LAN address space to be 192.168.1.0/24, you probably have to change those accordingly:

interface GigabitEthernet1/0
 description Link to ISP A
 ip address 41.10.20.2 255.255.255.252
 no ip route-cache

interface GigabitEthernet1/1
 description Link to ISP B
 ip address 212.101.65.6 255.255.255.252
 no ip route-cache

router bgp 10
 bgp dampening
 neighbor 41.10.20.1 remote-as 20
 neighbor 41.10.20.1 route-map ISP_LOW in

 neighbor 212.101.65.5 remote-as 50
 neighbor 212.101.65.5 route-map ISP_HIGH in

 auto-summary

route-map ISP_LOW permit 10
 match ip address 1
 set weight 100

route-map ISP_LOW permit 20
 match ip address 2

route-map ISP_HIGH permit 10
 match ip address 1

route-map ISP_HIGH permit 20
 match ip address 2
 set weight 100

access-list 1 permit 0.0.0.0 127.255.255.255
access-list 2 deny 0.0.0.0 127.255.255.255
access-list 2 permit any

[a.alekseev]

I would like to admit that unequal load-balancing is also possible...

[Julio E. Moisa]

Hi

You can use BGP attributes like local preference and AS Path in order to have symmetric traffic, also in order to avoid flapping you can configure fast fallover and BGP dampening.