BGP Config CE to ISP

[Mokhalil82]

Hi

We have a few sites and currently we have purchased MPLS from the ISP to provide connectivity between the sites. The ISP is in the process of installing the lines at each site and they have provided us with a /30 public subnet for each site, on e of the IPs being the GW. 

Plan is to configure DMVPN over this MPLS. But to achieve initial connectivity between the sites, how do I configure my routers at each site. Is it just a matter on configuring it with the public IP and having a default route to the gateway, or do I need some BGP config for CE to PE peering. 

Its my 1st attempt so just trying to see how to go about this.

Thanks

[Jon Marshall]

Depends on the SP ie. you need to talk to them to find out what they support and how they want to do it.

There are a number of options but the commonest are -

1) static route(s) pointing to SP end and they would then need to know each of your sites subnets to add statics to their end

2) more commonly BGP is used to exchange routes and if you have a lot of subnets or are going to be having multiple connections to each site I suspect they will want to use that.

There are other ways but the above are the most used as far as I know.

Edit - I haven't run DMVPN across MPLS so this may complicate things ie. you might want to mention that to them when you talk to them.

It may have some bearing on which routing protocol to use if they support multiple options.

Perhaps other posters can add to the above.

Jon

[Mokhalil82]

Hi Jon

Most likely I believe it is BGP, im just thing of the config this may require. Would it be something as follows considering i am using 192.168.1.0/30 for the ce to pe link.

router bgp 65001

no synchronization

bgp log-neighbor-changes

network 192.168.2.0 mask 255.255.255.0 (my internal network)

neighbor 192.168.1.1 remote-as 1

no auto-summary

Thanks

[Jon Marshall · Accepted solution]

Yes that would be fine as long as -

1) there is matching route for 192.168.2.0/24 with the exact subnet mask as well in the IP routing table.

2) you are using a different AS per site. You can use the same one but you need additional configuration because by default BGP will not accept any routes with it's own AS in them.

In addition you don't say whether this router is the default gateway for clients or not.

If it isn't then you also need to redistribute your BGP learned routes into any IGP you are running.

Jon

[Mokhalil82]

Thanks Jon

The network will be a hub and spoke setup with internet breakout at the hub site. So the spoke sites will use the routers as their default gateway. As part of the bigger picture we are implenting IWAN with Performance routing. So this BGP into isp and the dmvpn is going to be the initial setup to get connectivity between the sites.