[117517] in North American Network Operators' Group
RE:
daemon@ATHENA.MIT.EDU (Brian Dickson)
Wed Sep 16 16:05:03 2009
From: Brian Dickson <Brian.Dickson@concertia.com>
To: Richard A Steenbergen <ras@e-gerbil.net>, Michael Ruiz
<mruiz@telwestservices.com>
Date: Wed, 16 Sep 2009 17:03:42 -0300
In-Reply-To: <20090916190705.GU51443@gerbil.cluepon.net>
Cc: "nanog@nanog.org" <nanog@nanog.org>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
RAS wrote:
[ lots of good stuff elided for brevity ]
> c) lower the mtu on the ds3 interface to 1500.
This will have another benefit, if it is done to all such interfaces on the=
two devices.
(Where by "all such interfaces", I mean "everything with set-able MTU > 150=
0".)
Configuring one common MTU size on the interfaces, means the buffer pool on=
the box will switch from several pools of varying sizes, to one pool.
The number of buffers per pool get pro-rated by speed * buffer size, so hig=
h-speed, high-MTU interfaces get a gigantic chunk of buffer space.
Once you reduce things to one pool, you significantly reduce the likelihood=
of buffer starvation.
Note that the discussion on benefits to buffers is old info, and may even b=
e moot these days, but buffers are fundamental enough that I doubt it.
However, the original problem, iBGP not working, will definitely be resolve=
d by this.
Note also, changing this often won't take effect until a reboot, and/or may=
result in buffer re-carving with an attendant "hit" of up to 30 seconds of=
no forwarding packets (!!). You've been warned...
In other words, plan this carefully, and make sure you have remote hands av=
ailable or are on site. This qualifies as "deep voodoo". ;-)
Brian
