BGP 3750 behind 2851

thomuff · ‎10-11-2010

Today, I am running a 4507R strictly Layer 2 with a trunk port to 2851 configured with multiple subinterfaces. This router runs BGP AS 55555 and a WAN link to MPLS cloud.

The plan is to replace the 4507 with a stack of Catalyst 3750 switches. We want to move the subinterfaces to the Calayste 3750 and then have a point to point from the 3750 stack to the 2851. We do not want to remove this 2851 in place for Netflow, QOS, Voice gateway, etc...

Question: What is the best way to implement routing?

Should I configure BGP on the 3750 stack with vlan interfaces? with a seperate AS? same AS?

or

on 3750, just configure vlan interfaces with a static route pointing to the router and turn on ip routing but no routing protocol

on the 2851 router static routes and network statements to route the traffic back to the Catalyst.

At this time, we will not run etherchannel between the the router and the WAN channels.

Edison Ortiz · ‎10-11-2010

One design would be configuring an IGP such as OSPF between the 2800 ISR router and the 3750 Stack.

On the 3750 stack, list all the connected interfaces under the OSPF routing process.

On the 2800 ISR, list the 3750 connected interface under the OSPF routing process and issue a default information originate always command.

Additionally, on the 2800 ISR redistribute the OSPF subnets into BGP.

Regards,

Edison

Robert Taylor · ‎10-11-2010

Other than this MPLS link for site to site traffic, do you have any other backup paths to those remote networks?

If not, then static routing could be used ... but I would not use it unless I was configuring a default route from the 3750 to the 2800.

If there is some other internet connection on a different device, then a default static on the 3750 would not make much sense. Thus, I would redistribute the mpls learned remote networks into some other routing protocol (ospf/eigrp) to the 3750 stack.

This way, you can dynamically advertise your local subnets from the 3750 to the mpls router, which would announce them across the mpls cloud to your remote sites, and vice versa.

This help?