Internet BGP question

[dne222]

Hi together,

i want to ask you for a good way to solve a problem:

One of my friends has an AS connected to two different providers. The routers have the full BGB Table and the routingtable prefers the provider that is closest to the destination somewhere in the internet. If now the provider with the closest way has a problem (or maybe in the way - not in his network) what mechanism is the best to solve the problem for the clients ? Set up manually ip routes with better costs ? configure manually the routes from that provider-router with higher costs than the other ? What was the easyiest an best way?

Thanks in advance

[John Blakley]

If I understand your question and you're peering with 2 ISPs, you'd want to prefer one over the other. You can use a weight or local preference and a route map to prefer ISPA over ISPB, and then when ISPA stops advertising routes because it's peer down the line stopped for some reason, if ISPB knows how to get to it, then your router will start transmitting to that router instead.

HTH,

John

[Kishore Chennupati]

HI,

If you have one  router (Cisco) connected to 2 ISP's then you can use WEIGHT,AS-PATH to influence your routing. ISP-A primary and ISP-B secondary.

But if you have 2 routers(cisco, non-cisco) each connected to the ISP's then you can use local preference,AS_PATH to infuence your routing.

You can also use communities to achieve the above. Just check with the ISP if you intend to do so.

HTH,

Regards

Kishore

please rate if helpful

[mile.ljepojevic]

By default, if there is any issue on network or network path, if ISP has multiple paths, BGP will re-converge and bypass part of the network that is down. On the other hand, if there is occasional packet loss, or congestion, BGP is not aware of it and there will be no change in routing traffic.

You can use weight and local preference to manipulate your outgoing traffic, and you can hope to achieve something with AS-PATH prepend for the incoming traffic. Either way, if you have full bgp routing tables coming from both your ISP and if you can pinpoint which public prefixes has issues, you can change weight on routes received from your backup router and re-route your outgoing traffic.

Honestly, I wounldn't to any of that. If my primary ISP has issues, I would shut it down and use my backup ISP for a while.