BGP One Router Two ISP Failover

[dmitriy.krinitsyn]

Hi

I need a help. I have an ISR 2921 connected with two ISP on BGP. I anounce them one network 37.139.*.0/24.

How can I make a failover with this? I need that all traffic goes to ISP1 and if internet down all traffic goes to ISP2. 

Thanks for help! 

[paul driver · Accepted solution]

Hello
As this sounds like you have just the one router connecting to two ISP's?

You don't mention if ithey are same or different ISP's, In any case I am assuming the latter, So you should be able to utilize the Weight and As-path path attributes to accommodate your request.

For as-path prepending I would suggest liaise with your ISP's to make they allow prepending, as they could easily over-wright such action


Example:
access-list 10 permit 37.139.x.0 0.0.0.255

ip as-path access-list 10 permit ^$ <---------------(to stop your site becoming a transit for either ISP, it just advertises local prefixes and not each others ISP routes)

route-map ISP2_rm permit 10
match ip address 10
set as-path prepend Y Y Y

router bgp Y
network 37.139.x.0 mask 255.255.255.0
neighbor <ISP1> remote-as X
neighbor <ISP1> weight 50000 <------------------Outgoing traffic proffered over this path
neighbor <ISP1> filter-list 10 out <----------------- just advertise local routes
neighbor <ISP2> remote-as Z
neighbor <ISP2> weight 10000
neighbor <ISP2> route-map ISP2_rm out<----------------ISP2 see your advertise network less preferred and should go via ISP1 to get to it.
neighbor <ISP2> filter-list 10 out  <----------------- just advertise local routes

res
Paul

[dmitriy.krinitsyn]

You don't mention if ithey are same or different ISP's, In any case I am assuming the latter

Yes, you are right.

Thanks for help! I thought the same but wanted to make sure.