Need your advise on a network design with MPLS WAN links

[Difan Zhao]

Hi experts,

I want to do this right for the customer and I need your advise on the network design. Please have a look at the simplified network diagram.

The goal is to use MPLS as the primary path and use the serial PPP link as backup when MPLS fails. I read on the internet that the BGP is recommended to interface with the SP and do redistribution on Core2 and Branch router2. However in order to prefer MPLS, the only way I can think of is to change the routing protocol from OSPF to BGP on the serial link and then play with the path attributes. Will this solution work?

There is VOIP application running on the network. I know that BGP converges relatively slow. I don't anticipate not losing a single call. However how long will this design take to reconverge? I know that some BGP timers can be tuned. The recommended config is highly appreciated...

There will be eventually five sites on the MPLS cloud. Right now they are all in their own OSPF area.

Please let me know if there is a better design for this.

Thanks very much!

Difan

[huangedmc]

If you really want to stick w/ OSPF, you can make the MPLS path more preferred by creating a "super backbone" by utilizing a sham-link.

However, that can complicate things, but just wanted to point out it's an option.

I personally prefer BGP, since it's very granular, and you can manipulate the paths w/ all sorts of attributes.

Also when your remote sites start to grow, BGP can scale in terms of number of prefixes just because of its nature.

If you're concerned w/ reconvergence for critical apps or VoIP, you can work w/ your carrier to come to an acceptable timer.

We lowered ours from the default 60/180 to 10/30.

HTH

[Difan Zhao]

Thank you!