Description of problem: Network manager does not change the MTU when instructed by nmcli, GUI or editing the config files
Version-Release number of selected component (if applicable):
Steps to Reproduce:
1. nmcli connection modify p4p1 802-3-ethernet.mtu 9000
2. Check that MTU=9000 has been added to /etc/sysconfig/network-scripts/ifcfg-p4p1
3. ifconfig shows that the MTU is still 1500, reboot and still 1500
4. ifconfig p4p1 mtu 9000 sets the MTU for the current boot
p4p1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
ifconfig shows that the interface MTU is 9000 and survives reboots.
p4p1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 9000
This same behaviour on Centos 7.
There was a problem of setting MTU from DHCP (bug 1047083), but that is fixed just in -41.git20131003.fc20.
However, in your case, it may only be a configuration issue. Please realize that your first command only modifies a connection profile named p4p1. You need to re-activate it so that the changes take effect. Is the MTU correctly applied when you do nmcli con up p4p1?
Can you check what connection is activated after reboot?
$ nmcli con show active
And list all connections
$ nmcli con show
Can you attach /var/log/messages too?
I just tried it in an up-to-date VM
# nmcli connection show active
nmcli connection show active
NAME UUID DEVICES DEFAULT VPN MASTER-PATH
eth0 b3394931-b18b-49ab-b7cd-042d13ee6b53 eth0 yes no --
# nmcli con show
nmcli con show
NAME UUID TYPE TIMESTAMP-REAL
eth0 b3394931-b18b-49ab-b7cd-042d13ee6b53 802-3-ethernet Tue 11 Nov 2014 11:29:28 AEST
# nmcli connection modify eth0 802-3-ethernet.MTU 9000
# cat ifcfg-eth0
# nmcli connection up eth0
eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 9000
Also MTU=9000 after a reboot.
The only difference to previous attempt was the 'nmcli connection up eth0' unless some other update fixed it.
This is the expected behavior.
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