[3421] in linux-net channel archive
MTU problems
daemon@ATHENA.MIT.EDU (Michael Lausch)
Sun Jun 23 13:18:19 1996
To: linux-ppp@vger.rutgers.edu
cc: linux-net@vger.rutgers.edu
Date: Sun, 23 Jun 1996 19:07:00 +0200
From: Michael Lausch <mla@gams.co.at>
Maybe it's just my fault and i'm doing something wrong but we
encountered an error with MTU discovery in Linux 2.0.0. with MTU
Discovery enabled.
I discovered this behaviouir whena Mac was crashing if using a MRU of 1500
over PPP. So we decided to reduce the MRU on the Mac. For testing and
verification purposes I've emulated the situation with the
following setup:
mru 236 mtu 236
ppp-client (lottchen.gams.at) <----> ppp-server(bononunu.gams.co.at)
PPP ^
|
| Ethernet
|
V
File Server (loki.gams.co.at)
The MTU values are set correctly (checked with ifconfig).
The setup was done using the following ommands:
PPP Server:
/usr/sbin/pppd silent proxyarp -defaultroute crtscts ppp-dialin2
PPP Client:
/usr/sbin/pppd defaultroute crtscts modem mru 236 :
Then i'm doing a file copy with scp.
Icmpinfo on loki.gams.co.at shows the following:
Jun 20 16:46:22 ICMP_Dest_Unreachable[Frag] < xxx.xxx.xxx.xxx
[bononunu.gams.co.at] > xxx.xxx.xxx.xxx [ppp-dialin2.gams.co.at] sp=5632
dp=1022 seq=0x3da9dadd sz=304(+20)
Tcpdump on the Ethernet shows the following:
16:46:19.305143 ppp-dialin2.gams.co.at.1022 > loki.gams.co.at.22: S
1298278750:1298278750(0) win 512 <mss 1460>
16:46:19.305143 loki.gams.co.at.22 > ppp-dialin2.gams.co.at.1022: S
1034541773:1034541773(0) ack 1298278751 win 31744 <mss 236>
16:46:22.295810 loki.gams.co.at.22 > ppp-dialin2.gams.co.at.1022: S
1034541773:1034541773(0) ack 1298278751 win 31744 <mss 236>
16:46:22.335819 ppp-dialin2.gams.co.at.1022 > loki.gams.co.at.22: . ack 1
win 31744 [tos 0x10]
16:46:22.335819 loki.gams.co.at.22 > ppp-dialin2.gams.co.at.1022: P
1:16(15) ack 1 win 31744 (DF) [tos 0x10]
16:46:22.375828 ppp-dialin2.gams.co.at.1022 > loki.gams.co.at.22: P
1:16(15) ack 16 win 31744 (DF) [tos 0x10]
16:46:22.375828 loki.gams.co.at.22 > ppp-dialin2.gams.co.at.1022: P
252:292(40) ack 16 win 31744 (DF) [tos 0x10]
16:46:22.415836 ppp-dialin2.gams.co.at.1022 > loki.gams.co.at.22: . ack 16
win 31744 [tos 0x10]
16:46:22.575872 truncated-ip - 44 bytes missing!193.46.122.142 >
ppp-dialin2.gams.co.at: (frag 10725:256@1824) [tos 0x10]
16:46:22.575872 truncated-ip - 204 bytes missing!193.46.179.126 >
ppp-dialin2.gams.co.at: (frag 10725:256@544) [tos 0x10]
16:46:22.625883 ppp-dialin2.gams.co.at.1022 > loki.gams.co.at.22: . ack 16
win 31744 [tos 0x10]
16:46:22.975961 truncated-ip - 44 bytes missing!193.46.122.136 >
ppp-dialin2.gams.co.at: (frag 10731:256@1824) [tos 0x10]
16:46:22.975961 truncated-ip - 204 bytes missing!193.46.179.120 >
ppp-dialin2.gams.co.at: (frag 10731:256@544) [tos 0x10]
16:46:23.776138 truncated-ip - 44 bytes missing!193.46.122.122 >
ppp-dialin2.gams.co.at: (frag 10745:256@1824) [tos 0x10]
16:46:23.776138 truncated-ip - 204 bytes missing!193.46.179.106 >
ppp-dialin2.gams.co.at: (frag 10745:256@544) [tos 0x10]
16:46:25.376491 truncated-ip - 44 bytes missing!193.46.121.91 >
ppp-dialin2.gams.co.at: (frag 10765:256@1824) [tos 0x10]
16:46:25.376491 truncated-ip - 204 bytes missing!193.46.206.113 >
ppp-dialin2.gams.co.at: (frag 10765:256@544) [tos 0x10]
16:46:28.577193 truncated-ip - 44 bytes missing!193.46.121.55 >
ppp-dialin2.gams.co.at: (frag 10801:256@1824) [tos 0x10]
16:46:28.577193 truncated-ip - 204 bytes missing!193.46.206.77 >
ppp-dialin2.gams.co.at: (frag 10801:256@544) [tos 0x10]
16:46:34.978581 truncated-ip - 44 bytes missing!193.46.120.242 >
ppp-dialin2.gams.co.at: (frag 10870:256@1824) [tos 0x10]
16:46:34.978581 truncated-ip - 204 bytes missing!193.46.206.8 >
ppp-dialin2.gams.co.at: (frag 10870:256@544) [tos 0x10]
16:46:47.781406 truncated-ip - 44 bytes missing!193.46.120.102 >
ppp-dialin2.gams.co.at: (frag 11010:256@1824) [tos 0x10]
16:46:47.781406 truncated-ip - 204 bytes missing!
and the connection hangs.
What bothers me most are the wrong IP numbers: only the first two
octets of the IP addresses of the fragments are correct. Is there
something wrong, or am i just clueless.
---
g.a.m.s. edv dienstleistungen gmbh
finger mla@spirit.luga.or.at for PGP key
<http://www.gams.at/~mla>
