Routing options

pattbo · ‎10-15-2008

Hey everyone, I am looking for a solution to a routing decision problem. Maybe I have been doing this "the old way" so long I just can't see any other options.... so I'd thought I'd reach out and ask everyone for input.

I have 4 sites, fully meshed via GRE tunnels. I use EIGRP now. I need routing decisions to be based on lowest latency path, and not lowest hop count. I have a latency sensitive app, that runs between all sites and sometimes a 2 hop path has less total latency then the direct 1 hop path. EIGRP continues to use the direct path. For example, the 2 hop path equals 8ms while the 1 hop path is 20ms.

Can I use EIGRP to make that decision real time? Other protocols?

I understand that EIGRP is using bw and delay. BW is set equal on the tunnels and delay varies but not enough to make the decision to use the 2hop, lower latency path?

Any thoughts on the matter?

Thanks in advance.

Edison Ortiz · ‎10-15-2008

Your ordinary routing protocol does not have that kind of intelligence.

You may want to look into Cisco's PfR:

http://www.cisco.com/en/US/prod/collateral/iosswrel/ps6537/ps6554/ps6599/ps8787/product_data_sheet0900aecd806c4ee4.html

HTH,

__

Edison.

Istvan_Rabai · ‎10-15-2008

Hi Patrick,

Another simple solution may be to change the delay parameter on the tunnel interfaces using the "delay" command to a number where EIGRP will decide as you want it to decide.

PfR is a very good solution when the real physical delay changes over time, then PfR can dinamically switch over to the lowest latency path.

Cheers:

Istvan

Joseph W. Doherty · ‎10-15-2008

I too agree with Istvan, adjust delay to reflect your network's static performance.

As for dynamic performance, both OER and PfR can do that today, but not with EIGRP. They'll only work with statics and BGP. However, additional IGP support is on the roadmap for PfR. (I think I had read, dynamic analysis was planned for EIGRP, but if it was, I would suspect it would now be incorporated in PfR/EIGRP.)