WAN newbie question about BGP to connect edge router to provider MPLS cloud

Alvaro · ‎05-09-2014

WAN newbie
Good afternoon, so I have been tasked with setting up BGP on our MPLS cloud, my organization has 4 sites, 3 of which are connected through a MPLS cloud and the fourth is connected through an IPsec tunnel. The MPLS cloud was originally setup with static routes that the carrier had to create on their end to get connectivity between our sites. I have some experience with LAN and other things but I never really did much with WAN connectivity. We're making changes and it's been decided to make the change to BGP in order to take away the complexity of static routes. I did some reading on BGP and it seems pretty straight forward on what I have to do on our edge routers.

In the MPLS cloud we have three sites, Miami, Los Angeles, and our DR site and we are soon to add site Boston. Miami is our main office and it has a tunnel to our international affiliate to connect to some external resources, site Los Angeles is currently accessing those subnets through the static routes in the MPLS. I have already created another tunnel in our DR site to those same subnets and our plan is have site Los Angeles and Boston connect to those subnets through our DR path via the MPLS, our Miami site will keep the existing tunnel and they will keep accessing those resources through that tunnel. I already have the AS number from the carrier and they told me that we need to drop the static route as I add the networks in BGP. I just had a question about the commands that I need to put on our edge routers in order to publish the networks properly. The broker told me we can use our own AS numbers so I was going to use 10, 20, 30 and 40 for each site and just put the AS number for the provider. If I do the following config on each of our edge routers will that accomplish what I need to do? of course I would have to change the networks for each of the routers, or maybe do redistribute connected or redistribute static in the sites that only have the local subnets.

router bgp 10
no synchronization
bgp log-neighbor-changes
network 10.10.20.0
network 10.10.30.0
network 10.10.40.0
neighbor 65.65.65.65 remote-as 10000
no auto-summary

Thanks very much for the help, I'm a little green when it comes to WAN connectivity.

milan.kulik · ‎05-09-2014

Hi,

a) Your provider should tell you which AS number you need to configure on each of your sites. It needs to be configured properly on both sides to establish a BGP peering.

b) You need to get the subnets you want to advertise from a site to the router RIB first some way (directly connected, static, IGP).

Then you can use the "network 10.x.x.x mask y" command.

Or you can redistribute the routes (connected, static, IGP) to BGP (using a route-map possibly if you need to redistribute only some of them).

Best regards,

Milan

Alvaro · ‎05-12-2014

Thanks for the answer Milan, we currently have it all setup with static routes, the previous IT admins had set it up in a hurry and just provided the carrier with a list of static routes and the carrier set them up on their end. Have any idea what will happen with those static routes? what is there is a conflict? what takes precedense, the static route or the route advertised by BGP? Thanks again for the info.

milan.kulik · ‎05-13-2014

Hi,

if the provider router receives a prefix from you viua BGP and he has got a static route configured for the same static, the static route wins on his router (the administrative distance of a static route is better than any dynamic protocol one).

So the correct configuration would be to remove the static routes from the provider routers when you start advertising them via BGP.

You can start with advertising one prefix and asking the provider to remove the static route for the same prefix.

If everything works fine, you can advertise all your prefixes and ask the provider to remove static routes for all of them.

Bets regards,

Milan

alkiswani · ‎05-14-2014

Hello Alvaro,

It seems to me that you are mistaking the static routes you currently have on your side of the network and the static routes your ISP currently has for you. They are related to the MPLS connectivity between your offices to create a partial or full mesh. And has nothing to do with BGP.

As for the BGP setup, your broker did not say the correct thing when said that you can use any BGP AS you want. He/she would be right only if you are setting up your private BGP network, not a public one.

As for a real BGP setup, you will need to get an AS from ARIN (https://www.arin.net/resources/request/asn.html). And have in mind, that you can't just apply and get one, there are requirements that you must fulfill in order for you to get one.

When and if you get it, then you will need to give your ISP or ISPs a call and work fill the appropriate paper work and provide the needed info (the peer IP address of the BGP neighbor, the AS number of the your ISP to that neighbor, the password of the session and so on.. ). You would then work with their techs to establish the BGP neighboring, and agree which routes you want to get and or advertise..

If you are only talking about replacing the static routes that your current connectivity is using (the MPLS connectivity between your sites), why not go with OSPF, EIGRP or even RIP2. As the MPLS cloud of your ISP will encapsulate the traffic of these routing protocols and would be hidden till they reach the other sides of your network. Remember, the ISP uses a completely separate routing table of your sites (VRF) so all of your routing in their routing table is specific to your networks.

I hope this helps you a bit.

milan.kulik · ‎05-14-2014

Hi,

my understandign was we are not talking about a connection to the Internet but to an MPLS provided by a provider?

In that case you don't need to any public AS number from ARIN.

You just need the provider to tell you the AS number you should use and the AS number of his router you are peering to. He also should tell you which IP addresses to use for peering and a BGP session password optionally.

Of course you can use a different routing protocol to peer with the provider but BGP is the most robust and flexible one.

Best regards,

Milan

alkiswani · ‎05-15-2014

If this is the case, in my opinion, BGP would be the worst protocol to use. Its the slowest convergence of all routing protocols and is designed for a very large enterprise kind of networks. Any other routing protocol would be a lot faster and would be the better choice than BGP.

Thanks..