Bug 1123320 - Networkmanager does not set the mtu
Summary: Networkmanager does not set the mtu
Alias: None
Product: Fedora
Classification: Fedora
Component: NetworkManager
Version: 20
Hardware: Unspecified
OS: Unspecified
Target Milestone: ---
Assignee: Dan Williams
QA Contact: Fedora Extras Quality Assurance
Depends On:
TreeView+ depends on / blocked
Reported: 2014-07-25 10:05 UTC by Darryl Bond
Modified: 2015-06-29 21:45 UTC (History)
4 users (show)

Fixed In Version:
Doc Type: Bug Fix
Doc Text:
Clone Of:
Last Closed: 2015-06-29 21:45:24 UTC

Attachments (Terms of Use)

Description Darryl Bond 2014-07-25 10:05:46 UTC
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):
NetworkManager.x86_64           1:

How reproducible:

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
Actual results:
ifconfig p4p1
p4p1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500

Expected results:
ifconfig shows that the interface MTU is 9000 and survives reboots.
p4p1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 9000

Additional info:
This same behaviour on Centos 7.

Comment 1 Jirka Klimes 2014-11-10 08:38:14 UTC
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?

Comment 2 Darryl Bond 2014-11-11 01:37:50 UTC
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
# ifconfig
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.

Comment 3 Fedora End Of Life 2015-05-29 12:28:16 UTC
This message is a reminder that Fedora 20 is nearing its end of life.
Approximately 4 (four) weeks from now Fedora will stop maintaining
and issuing updates for Fedora 20. It is Fedora's policy to close all
bug reports from releases that are no longer maintained. At that time
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Comment 4 Fedora End Of Life 2015-06-29 21:45:24 UTC
Fedora 20 changed to end-of-life (EOL) status on 2015-06-23. Fedora 20 is
no longer maintained, which means that it will not receive any further
security or bug fix updates. As a result we are closing this bug.

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