Subject: Path MTU discovery
To: None <tech-net@NetBSD.ORG>
From: Matthias Scheler <tron@lyssa.owl.de>
List: tech-net
Date: 10/28/1997 08:39:18
Hi,
I have two questions concerning the path MTU discovery support in
NetBSD 1.3_ALPHA.
1.) Does it actually work?
I tried it a few minutes ago with a this network structure:
lyssa.owl.de
|
ethernet (MTU 1500)
|
V
colwyn.owl.de
|
PPP (MTU 576)
|
some more hosts (MTU 1500)
|
V
paderborn.core.owl.de (Linux 1.2.13)
|
Slip (MTU 296)
|
V
pri.owl.de (Linux 2.0.28)
|
some more hosts (MTU >=1500)
|
V
gigaserv.uni-paderborn.de (Sun-OS 5.5)
I activate path MTU discovery on "lyssa.owl.de" and started a FTP session
with "gigaserv.uni-paderborn.de". Due to small packet sizes the connet
was no problem. But when I tried to upload something the transfer freezed
after a short time. "tcpdump" shows the ICMP messages from the router but
there's obviously no reaction on them from the NetBSD box:
09:24:50.789611 paderborn.core.owl.de > lyssa.owl.de: icmp: gigaserv.uni-paderborn.de unreachable - need to frag [tos 0x8]
09:24:51.101310 paderborn.core.owl.de > lyssa.owl.de: icmp: gigaserv.uni-paderborn.de unreachable - need to frag [tos 0x8]
09:24:51.381404 paderborn.core.owl.de > lyssa.owl.de: icmp: gigaserv.uni-paderborn.de unreachable - need to frag [tos 0x8]
09:24:51.666498 paderborn.core.owl.de > lyssa.owl.de: icmp: gigaserv.uni-paderborn.de unreachable - need to frag [tos 0x8]
09:24:51.952147 paderborn.core.owl.de > lyssa.owl.de: icmp: gigaserv.uni-paderborn.de unreachable - need to frag [tos 0x8]
09:24:52.220703 paderborn.core.owl.de > lyssa.owl.de: icmp: gigaserv.uni-paderborn.de unreachable - need to frag [tos 0x8]
Has anybody successfully tried path MTU discovery?
2.) How can I list the MTU values which got discovered?
--
Matthias Scheler http://home.owl.de/~tron/