Re: 2.0.21: TCP hangs solved by disabling Path MTU Discovery

Eric Schenk (
Fri, 27 Sep 1996 13:04:12 -0400

"A.N.Kuznetsov" <> writes:
>Derrick J. Brashear (shadow@dementia.ORG) wrote:
>: I put back a piece of code that had been if 0'd out around 2.0.16 to get this
>: to work with the path mtu discovery, but when I posted the patch as a possible
>: fix for the PPP problems I was having, someone else posted that the patch was
>: in there because it was making something break on his machine. Who knows?
>As I understand, that piece of code is both harmless and useless.
>It can neither repair nor break something.

Without this peice of code alternating pure ACK and data packets have
different don't fragment bits. The result is that VJ compression can
never send a compressed TCP header during interactive traffic.
As far as I know this can't cause any trouble for path MTU discovery.
However, putting this piece of code in seems to reveal a bug in VJ
compression, either in our code, or the code on certain Annex systems.
I'm trying to track this down right now.

-- eric

Eric Schenk www:
Department of Computer Science email:
University of Toronto