[101616] in North American Network Operators' Group
Asymmetrical routing opinions/debate
daemon@ATHENA.MIT.EDU (Drew Weaver)
Mon Jan 14 10:24:13 2008
From: Drew Weaver <drew.weaver@thenap.com>
To: "nanog@merit.edu" <nanog@merit.edu>
Date: Mon, 14 Jan 2008 10:30:56 -0500
Errors-To: owner-nanog@merit.edu
Pardon me if I am using the wrong term, I am using the term Asymmet=
rical routing to describe a scenario in which a request packet enters a net=
work via one path and the response packet exits the network via a different=
path.
For example an ICMP ping request enters a network via ISP A and the reply l=
eaves via ISP B (due to multi-homing on both networks, and or some kind of =
manual or automatic 'tweaking' of route preferences on one end or the other=
).
I haven't noticed too many instances of this causing huge performance probl=
ems, but I have noticed some, has anyone noticed any instances in the real =
world where this has actually caused performance gains over symmetrical rou=
ting? Also in a multi-homed environment is there any way to automatically l=
imit or control the amount of Asymmetrical routing which takes place? (shou=
ld you?) I have read a few papers [what few I could find] and they are conf=
licted about whether or not it is a real problem for performance of applica=
tions although I cannot see how it wouldn't be. Has there been any real com=
munity consensus on this issue published that I may have overlooked?
Thank you,
-Drew
