Redundant CE routers (same subnet) for MPLS PE Connection

[Keith Nelson]

Started with a single CE datacenter router that is BGP peering with a single PE router for connection to our ISP MPLS network. There are other locations as well, and all of our routers use the same BGP AS. The ISP has their own AS, so we are using eBGP and each location advertises a few routes for MPLS. For outbound traffic we can essentially use the default route.

Now add a second CE router to the datacenter and BGP peer to the same BGP neighbor as the first CE router. Both CE routers are on the same network to the ISP and connect to the ISP router via L2 switch.  The ISP added the second router as an additional neighbor so both CE routers are peering to the same ISP PE router/IP. The CE routers can see each other via internal EIGRP connection and also via the switch to the ISP.  Both CE routers have the same BGP config except for local IP address of the ISP facing port.

The goal is redundancy should one of our CE routers go down and the ability to ingress/egress from both CE routers. Not as good as 2 separate ISP connections, but all we could get.I haven't found a single example of doing this and it looks like an unsupprted configuration by most ISPs.

By default all BGP inbound and outbound traffic uses the first CE router. By advertising local preferences, I hope to split the inbound/outbound traffic between our routers and provide redundancy. Is this a crazy idea?  Our datacenter traffic is also highly asymmetric, so being able to egress traffic from either router would really help.

Any ideas or problems that might occur?  I'm new to BGP, but this seems like it will work?

Thanks for any comments or links to documentation of this scenario.

-Keith

[smitesh kharecha]

Hi Keith,

I'm confused regarding your requirement.

Correct me if wrong..

-You want to have 2 router at CE configured as such that if one fails, second can take over the traffic.

If this is your requirement, for outgoing traffic you can setup simple HSRP solution and for incoming traffic keep the BGP config same on both the router and configure your primary router with higher local preference.

- Using two router, one for ingress and another for egress, in simle terms one for outgoing and one for incoming, is calling asymmetric routing. Assymetric routing is  not an issue if it is designed to operate that way.

HTH,

Smitesh

[Keith Nelson]

Thanks Smitesh. You correctly understand what we want to accomplish. I assume the HSRP would be on the client side of the routers? So the internal clients would hit our CE routers via the VIP. Would GLBP work better for load sharing? I was hoping to accomplish inbound/outbound load sharing with BGP. I know it wouldn't be perfect. Was mostly worried I was doing something fundamentally wrong by having 2 CE routers peered over a single link to the same ISP interface. BTW our routers are 7206-NPE400 on IOS 12.2.

Appreciate your comments and insight. Was also pleasantly surprised with how quickly you responded.

Thanks.

-Keith

Sent from Cisco Technical Support iPad App

[Keith Nelson · Accepted solution]

Sorry, the routers are running 12.3(20).

Keith

[smitesh kharecha · Accepted solution]

Hi Keith,

Let take example for sake of simplicity.

Let assume you are have pool of 192.168.1.0 /24 on your LAN side.

For any incoming traffic to your site, you can configure BGP such that you announce subnet 192.168.1.0/25 on R1 and 192.168.1.128/25 on R2.

I suggested HSRP for outgoing traffic, because you asked for redundancy and not load-sharing. If your goal is load sharing; definately GLBP would be better.

Another possibility would be running iBGP between R1 and R2 along with HSRP on LAN end.

Please rate if helpful.

HTH,

Smitesh

[Keith Nelson]

Thanks for the example and explanation. I had to let it soak in for a couple days. After re-reading your comments I understand. Thank you again.

Sent from Cisco Technical Support iPad App