Trying to set the MTU value for an interface: ifconfig eth0 mtu 1400 --causes the following error. SIOCSIFMTU:Invalid argument A workaround appears to be: echo 1 > /proc/sys/net/ipv4/ip_always_defrag echo 1 > /proc/sys/net/ipv4/ip_no_pmtu_disc This error occurred after upgrading to 6.1. I was able to use ifconfig to set the MTU on a different machine (identical processors and ethernet cards) that had 6.1 installed on it originally.
I can't reproduce this problem on either of my boxen. It may be that your networking configuration is different on the upgraded system, and a feature/limitation of the kernel or hardware is preventing you from changing the MTU.
*** This bug has been marked as a duplicate of 9129 ***
*** This bug has been marked as a duplicate of 9215 ***