BGP. How to set up failover?

Question

Computer networks

Hello.
There is a BGP router. Announces its network to two peers (2 different providers). I want to make one provider the main one, the second - the backup one. That is, the router should start announcing the network to the backup provider only if the session with the main one is broken. Is it feasible? If yes, tell me how.

Answer 1

You need to use more specific routes. Divide the network in half, but not less than / 24, for example / 21 into two / 22 each.
Then announce two /22 to the main provider, and a common /21 to the backup. Since /22 is less than /21, traffic will only go through the main one, as long as /22 is visible to the world through it. Well, that's all route: do not forget to register in RIPE.
Outgoing according to local-preference as mentioned above.

Answer 2

This is usually implemented using AS prepend. Those. announce the same to the reserve one, prepending your AS a couple of times. This way the fireover will happen faster.

Answer 3

I haven't worked much with BGP yet, but isn't AS Prepend for incoming traffic?

Answer 4

This is done through local-preference.
For example, Cisco IOS:

router bgp 33333
 neighbor 1.1.1.1 route-map localpref120 in
 neighbor 1.1.1.1 remote-as 11111
 neighbor 2.2.2.2 remote-as 22222

route-map localpref120 permit 10
 set local preference 120

If the provider with AS 11111 "falls", then the traffic will go through the provider with AS 22222.