2017-07-25 14:44 UTC

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IDProjectCategoryView StatusLast Update
0012204CentOS-7kernelpublic2017-02-14 18:38
Reportervijayxhost 
PriorityhighSeveritymajorReproducibilityalways
StatusnewResolutionopen 
Product Version7.2.1511 
Target VersionFixed in Version 
Summary0012204: mtu lowering not allowed
DescriptionThe kernel 3.10.0-327.36.3.el7.x86_64 is not allowing mtu to be lowered. It is taking the default value 1500. If you try to lower it to 1400 using whichever method, it stands 1500.
Steps To ReproduceUpdate kernel to 3.10.0-327.36.3.el7.x86_64. Add value MTU=1400 at /etc/sysconfig/network-scripts/ifcfg-XXXXX. Then restart network.

Try following commands

# ifconfig eth0 mtu 1400
OR
# ip link set dev eth0 mtu 1400
Additional InformationIf we boot with old kernel ie 3.10.0-123.el7.x86_64 it will work fine.
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~0028574

N3WWN (reporter)

Hi vijayxhost!

I have a fresh install of CentOS 7.2.1511, updated to the kernel you had an issue with, and cannot replicate the bug that you are reporting.

Here's what I did to replicate your system:

Fresh CentOS 7.2.1511 VM...

Updated /etc/yum.repos.d/CentOS-Base.repo to use vault for [updates] :
baseurl=http://vault.centos.org/7.2.1511/updates/x86_64/

# yum clean all
# yum upgrade-to kernel-3.10.0-327.36.3.el7.x86_64
# yum install net-tools
# reboot

Verify that running kernel is correct:
# uname -a
Linux localhost.localdomain 3.10.0-327.36.3.el7.x86_64 #1 SMP Mon Oct 24 16:09:20 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux

Check default MTU:
# ifconfig eth0 | grep mtu
eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500

Attempt to set MTU with ifconfig (worked):
# ifconfig eth0 mtu 1400
# ifconfig eth0 | grep mtu
eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1400

Attempt to set MTU with ip (worked):
# ip link set dev eth0 mtu 1300
# ifconfig eth0 | grep mtu
eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1300

Attempt to set MTU with network scripts (worked):
# echo "MTU=1450" >> /etc/sysconfig/network-scripts/ifcfg-eth0
# systemctl restart network
# ifconfig eth0 | grep mtu
eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1450

Can you provide any additional information that would help to replicate your scenario?

-Rich Alloway (RogueWave)
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-Issue History
Date Modified Username Field Change
2016-11-11 04:04 vijayxhost New Issue
2017-02-14 18:38 N3WWN Note Added: 0028574
+Issue History