[140365] in North American Network Operators' Group
RE: L3 ECMP over links with different RTT
daemon@ATHENA.MIT.EDU (Rettke, Brian)
Tue May 10 12:09:59 2011
From: "Rettke, Brian" <Brian.Rettke@cableone.biz>
To: "nanog@nanog.org" <nanog@nanog.org>
Date: Tue, 10 May 2011 09:09:50 -0700
In-Reply-To: <7BB25957-1B2F-477C-AE04-1D3DD6C538F2@muada.com>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
Per flow is generally the best method, and allows the employ of CEF (or the=
equivalent).
I've done load balancing in this method, and in others I've configured acti=
ve/standby for the reasons specified. It depends on whether you need true =
link redundancy more than the latency will affect traffic.
Another option, of course, is to apply PBR to get your low latency queues t=
o use the preferred link. I've done that as well, using EEM to remove the f=
orced next hop if the interface drops.
Sincerely,
Brian A . Rettke
RHCT, CCDP, CCNP, CCIP
Network Engineer, CableONE Internet Services
-----Original Message-----
From: Iljitsch van Beijnum [mailto:iljitsch@muada.com]
Sent: Tuesday, May 10, 2011 7:37 AM
To: Dikkema, Michael (Business Technology)
Cc: nanog@nanog.org
Subject: Re: L3 ECMP over links with different RTT
On 10 mei 2011, at 16:28, Dikkema, Michael (Business Technology) wrote:
> Is it foolish to build a L3 ECMP connection between 2 iBGP routers with o=
ne of the links having a 50% longer RTT?
No problem at all as long as you don't do per-packet load balancing but som=
ething that makes sure a single flow only goes over a single link. There ar=
e many ways to skin that particular cat, best practice is based on the 5-tu=
ple (source and dest addresses and ports and the protocol number) which wil=
l give you the best chance of having a similar load on both links as long a=
s you have at least some 1000 flows at any given time. With less granular l=
oad balancing there's a much bigger risk that one link will be full and the=
other more or less idle unless you have very, very many flows. You may wan=
t to use VLANs so you can load balance some stuff as per the above and manu=
ally balance some other stuff to go over the faster link.
