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New Member

Default Routes and BGP

I have several remote sites that connect to my central site via a provider MPLS network. These remote sites all use the central site for internet access. I would like to have a couple of these remote sites to use a secondary site for internet access. The secondary site also default routes everthing to the central site. How can I route this traffic through the secondary site out to the internet instead of it being routed back to the central site?

3 REPLIES
New Member

Re: Default Routes and BGP

Use a igp protocol ( rip,eigrp,ospf ) and put a default route to secondary site , in the central put the default route to local internet router.

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Raul

Re: Default Routes and BGP

well... you have BGP running there then you can have multiple option to influence the traffic pattern using attribute you can advertise routes with MED to make proper selection to particular remote site as well as at remote site you can influence the out bound traffic too...

regards

Devang Patel

Gold

Re: Default Routes and BGP

I assume from your question you are running BGP to your MPLS cloud. BGP has so many options and ways to do things it will all depend on how the MPLS vendor has set things up.

If we look at your issue in 2 separate parts.

You have a secondary site that you would like to use its own local internet connection rather than the central site.

you have a third site that you would like to use this secondary site rather than the main site

The first one may be as simple as changing the default route at the location. The key here is if you do a show ip route for a subnet at the main site on a remote site router. Do you have a route to it or does it use the default route. If you have a route then you can just put in a default route to point to your internet. Your router should contain a full list of routes in your network and know to send them to the MPLS and everthing else goes to the local internet.

If you do not have all the routes for the main site in the secondary site router you will need to inject them from the main site into the MPLS cloud. As long as your MPLS provider is not filtering them all your routers should now have all your subnets in your corporate network. The default is now only used to direct internet traffic to the main site.

So you can get the secondary site to use its own internet because it no longer needs to use the default from the MPLS cloud for anything. A static will override the bgp learned route.

Making the third site use the second is much harder. Even if you would make the second site also inject the default into the MPLS cloud BGP likes a single BEST route. So in the cloud it would either pick the main site or the secondary site for all other remote sites to use. Although there are options ot make it use more than a single best route which would then allow your remote site to filter based on orginating AS it does not solve the problem in the provider network. Once you get into the provider network from their viewpoint you are doing sourced based routing. They may be willing to do that but I would not be hopeful.

Although it has some disadvantages the simplest way is to construct a GRE tunnel between the site and the secondary site and put a static default route to this tunnel. Since the other site should also have a full routing table for your network it would only send intenet traffic to the tunnelled site. The only issue you have is that traffic coming back from the internet from the secondary site would not know to take the tunnel back to the third site. Because the secondary site has a route via the MPLS it will take that. You can force it to use the tunnel to get back but in this case async routing will most likely not hurt you.

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