[76805] in North American Network Operators' Group
Re: Smallest Transit MTU
daemon@ATHENA.MIT.EDU (Tony Rall)
Wed Dec 29 18:51:40 2004
In-Reply-To: <91B6F344-59E5-11D9-BF97-000D93B24C7A@isc.org>
To: nanog@merit.edu
From: Tony Rall <trall@almaden.ibm.com>
Date: Wed, 29 Dec 2004 15:48:02 -0800
Errors-To: owner-nanog-outgoing@merit.edu
On Wednesday, 2004-12-29 at 17:04 EST, Joe Abley <jabley@isc.org> wrote:
> On 29 Dec 2004, at 16:33, Tony Rall wrote:
> > But that only affects tcp traffic - it does nothing to help other
> > protocols.
>
> Are there any common examples of the DF bit being set on non-TCP
> packets?
Common? It depends on what you're doing. To some people, the only common
application is 80/tcp.
Remember that the DF bit is in the IP header - it can be on in any
protocol. I know that AIX and my old RH Linux (at least) defaults to
PMTUD enabled for tcp and udp. You can even see it in dns lookups.
> > The better solution is to ensure that PMTUD works correctly for your
> > network, and get on the case of any correspondent or provider for
> > which it doesn't.
>
> Making sure that pMTUd works in your own network doesn't solve the
> problem. You need to make sure it works properly in every other network
> with which you ever might want to exchange a 1500-byte packet.
I thought that's what I just said.
Tony Rall
