[29167] in North American Network Operators' Group
Re: PMTU-D: remember, your load balancer is broken
daemon@ATHENA.MIT.EDU (Valdis.Kletnieks@vt.edu)
Wed Jun 14 00:07:40 2000
Message-Id: <200006140405.e5E45UL12480@black-ice.cc.vt.edu>
To: "Steven M. Bellovin" <smb@research.att.com>
Cc: nanog@merit.edu
In-reply-to: Your message of "Tue, 13 Jun 2000 23:50:55 EDT."
<20000614035056.41F5935DC2@smb.research.att.com>
From: Valdis.Kletnieks@vt.edu
Date: Wed, 14 Jun 2000 00:05:30 -0400
Errors-To: owner-nanog-outgoing@merit.edu
On Tue, 13 Jun 2000 23:50:55 EDT, "Steven M. Bellovin" said:
> There are two places where it's very important. First, some server
> farms are on FDDI rings, so they have a higher MTU. Second -- and this
Yes, but I think I covered that in (a) - if you know there's a
bigger MTU, nail it down. I dread to think of a load-balancer
in the middle of a FDDI ring in a server farm ;)
> one is growing in importance -- tunnels, for IPsec, PPTP, etc. --
> generally have smaller MTUs. This very reply will travel over a tunnel
> with an MTU of, I believe, 1480.
Good point. It's been a long day, I wasn't QUITE thinking
straight. Another respondent commented that Windows98 apparently
nails an MTU of 576 on a dialup - Apparently I've not run into
any Windows98 people setting their clocks off the server I got
the numbers from. Also, he said that ADSL uses just under 1500.
I don't have a Win98 or ADSL handy to check. ;)
In any case, it's good fodder for an operational debate. ;)
Valdis Kletnieks
Operating Systems Analyst
Virginia Tech
