BGP and default gateway

[George Thomas]

Hello,

I have 2 offices that are connected via MPLS today. SP has BGP running to route between the two offices. We have OSPF as our internal routing protocols.  We are planning to add a layer 2 link between the offices (like a fiber from one office to the other) and plan to estabilish a neighbor relationship between the two office using OSPF over the Layer 2 link. After thats done, I would like to have the internet traffic go through the MPLS cloud and internal network traffic through the layer 2 link. How do I get that working? One of the offices in the central office and we have other offices connecting back to the main office through the MPLS cloud.

Thanks

[Nagendra Kumar Nainar]

Hi,

I assume BGP is the protocol you are running between your edge device and SP device. As you will have OSPF enabled on the new Link, you will receive all your branch office network prefix via both OSPF (through new link) and BGP (through SP).

Change your admin distance in OSPF below 20 (say 15 or 10) so that OSPF routes will be preferred over eBGP. This will make all your traffic to brnach office to prefer the new link.

I hope you will have a default route pointing to your SP (either via eBGP or a static route). This will take care of your internet traffic.

Make sure you have all prefix advertised throughOSPF and no default route via OSPF.

HTH,

Nagendra

[George Thomas]

Hi Nagendra,

Thanks for the response. This is kind of what I was thinking as well. I was going to increase the AD for BGP ( something greater than 110). Do you forsee any issues with this? Also, I will be pushing a default route from the BGP instance at the main office as we have centralised internet.

Thanks.

[Nagendra Kumar Nainar · Accepted solution]

Hi Thomas,

I see no issues. It should work.

Make sure, you dont get any default route via ospf.

HTH,

Nagendra

[George Thomas]

Thanks Nagendra.