Red Hat Bugzilla – Bug 486325
Wrong mtu value comes default and freezes ssh sessions
Last modified: 2010-12-05 02:00:34 EST
Description of problem:
Default mtu value is set to 1412 and cannot be configured.
Version-Release number of selected component (if applicable):
I'm running NetworkManager-vpnc-0.7.0-1.svn13.fc10.i386 but all systems has this bug
Steps to Reproduce:
1. connect to vpn
2. sudo ifconfig tun0 mtu 1412
3. connect a system via ssh
Ssh session freezes
Nothing should happen
Following workaround can be used with Network Manager Dispatcher script:
What's the MTU on the device that the VPN is using? vpnc requires only a few bytes of overhead (8) and thus it should really be using the MTU of the default device - the overhead.
MTU should be 1390. This dispatcher script solved the issue on Fedora 10 but not on Fedora 9.
if [ "$2" = "vpn-up" ]; then
/sbin/ifconfig "$1" mtu 1390
This bug has been triaged.
Fedora Bugzappers volunteer triage team
This bug appears to have been reported against 'rawhide' during the Fedora 11 development cycle.
Changing version to '11'.
More information and reason for this action is here:
I'm suffering from this as well.
Dan, isn't the 8 bytes scenario the best-case one? What about when doing NAT tunnelling? (which I am)
I found some thread claiming that Ciscos own client uses 1300 for MTU.
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