Subject: ssh freezes when used over slow connection (e.g. modem)
Date: Sun, 24 Nov 2002 23:39:10 -0500
Package: ssh
Version: 1:3.4p1-1
Severity: normal
When I use ssh to connect to a servers through the modem-line it freezes
(no input is accepted and no output is generated) whenever larger amounts
of data are to be transferred in short time. Typical "freezing points":
- paste a few paragraphs of text
- ls on directory with many files
- running program which generates plenty of output (e.g. latex) on
the remote computer
- listing backwards through e-mails in pine
Comparison to other packages
- never happened until upgraded to Woody from Potato
- does also happen with ssh2 package (but less often)
- does not happen with e.g. telnet
- never happened on machines comunicating over faster connections (e.g. LAN)
-- System Information
Debian Release: 3.0
Architecture: i386
Kernel: Linux pstros 2.4.18-k6 #1 Sun Apr 14 12:43:22 EST 2002 i586
Locale: LANG=C, LC_CTYPE=C
Versions of packages ssh depends on:
ii adduser 3.47 Add and remove users and groups
ii debconf 1.0.32 Debian configuration management sy
ii libc6 2.2.5-11.2 GNU C Library: Shared libraries an
ii libpam-modules 0.72-35 Pluggable Authentication Modules f
ii libpam0g 0.72-35 Pluggable Authentication Modules l
ii libssl0.9.6 0.9.6c-2.woody.1 SSL shared libraries
ii libwrap0 7.6-9 Wietse Venema's TCP wrappers libra
ii zlib1g 1:1.1.4-1 compression library - runtime
Subject: This doesn't appear to be connection dependent
Date: Tue, 28 Jan 2003 23:56:36 +0000
this bug appears to occur (the symptoms are nigh on identical) for me over
any speed of connection.
I've seen it with connections ranging from 56k modem, 512k dsl, 2mb dsl, and
aggregated 100mb links.
Also, it appears to be an upstream bug, since the same occurs with OS X.
If the problem happens again (extremely likely) i'll try and get some useful
info.
-Thom
Hi.
I'm helping out with some outstanding Debian OpenSSH bugs.
Regarding bug 170628, are there any packet filters, firewalls or NAT
devices between the client and server? The problem described is
characteristic of a MTU/fragmentation issue where an intermediate device
drops IP fragments. These tend to show up when interactive activity
generates enough traffic to send full-size packet(s).
From the bug report:
> Typical "freezing points":
> - paste a few paragraphs of text
Sends the whole buffer at once.
> - ls on directory with many files
Generates many screenfuls of data.
> - running program which generates plenty of output (e.g. latex) on
> the remote computer
Ditto.
> - listing backwards through e-mails in pine
Most terminal emulators can scroll down, however scrolling up requires
redrawing the entire screen.
Other common triggers:
* cat'ing a large file.
* starting an X11 app.
You can try setting the MTU of one end to be 576 (the minimum
permitted) with by executing "ifconfig ethX mtu 576". You only need
change one end, TCP will negotiate a maximum segment size (MSS) based on
the smaller of the two MTUs. This is not optimal but may work.
If your problem goes away then you can experiment to find the optimal
settings. For futher info, please see
http://marc.theaimsgroup.com/?l=openssh-unix-dev&m=102413585608801 .
-Daz.
--
Darren Tucker (dtucker at zip.com.au)
GPG key 8FF4FA69 / D9A3 86E9 7EEE AF4B B2D4 37C9 C982 80C7 8FF4 FA69
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