My syslog is full of errors from NetworkManager about setting the MTU for wireless adapter

NetworkManager keeps trying to set the MTU for my wifi connection to 9216 and then complain about it:

NetworkManager[9173]: <error> [1469713916.019478] [platform/nm-linux-platform.c:2489] sysctl_set(): platform-linux: sysctl: failed to set '/proc/sys/net/ipv6/conf/wlp3s0/mtu' to '9216': (22) Invalid argument 

wlp3s0 is my wireless adapter. I cannot find any configuration file that requests an MTU of 9216.

I've tried setting both MTU and IPV6_MTU to 1500 in my ifcfg file for the AP in question (/etc/sysconfig/network-scripts/ifcfg-MY_SSID_NAME):

IPV6_MTU="1500" MTU="1500" 

I even see NetworkManager acknowledging this in syslog:

NetworkManager[9173]: <info>  (wlp3s0): Lowering IPv6 MTU (9216) to match device MTU (1500) 

Which is then a few seconds later followed by a bout of:

NetworkManager[9173]: <error> [1469714284.500691] [platform/nm-linux-platform.c:2489] sysctl_set(): platform-linux: sysctl: failed to set '/proc/sys/net/ipv6/conf/wlp3s0/mtu' to '9216': (22) Invalid argument NetworkManager[9173]: <error> [1469714287.572734] [platform/nm-linux-platform.c:2489] sysctl_set(): platform-linux: sysctl: failed to set '/proc/sys/net/ipv6/conf/wlp3s0/mtu' to '9216': (22) Invalid argument NetworkManager[9173]: <error> [1469714300.474736] [platform/nm-linux-platform.c:2489] sysctl_set(): platform-linux: sysctl: failed to set '/proc/sys/net/ipv6/conf/wlp3s0/mtu' to '9216': (22) Invalid argument NetworkManager[9173]: <error> [1469714319.725995] [platform/nm-linux-platform.c:2489] sysctl_set(): platform-linux: sysctl: failed to set '/proc/sys/net/ipv6/conf/wlp3s0/mtu' to '9216': (22) Invalid argument NetworkManager[9173]: <error> [1469714336.521603] [platform/nm-linux-platform.c:2489] sysctl_set(): platform-linux: sysctl: failed to set '/proc/sys/net/ipv6/conf/wlp3s0/mtu' to '9216': (22) Invalid argument NetworkManager[9173]: <error> [1469714339.470093] [platform/nm-linux-platform.c:2489] sysctl_set(): platform-linux: sysctl: failed to set '/proc/sys/net/ipv6/conf/wlp3s0/mtu' to '9216': (22) Invalid argument 

....etc...

Assuming this request came from the router, I've turned off accept_ra and accept_ra_mtu:

# cat /proc/sys/net/ipv6/conf/wlp3s0/accept_ra 0 # cat /proc/sys/net/ipv6/conf/wlp3s0/accept_ra_mtu 0 

...to no avail...

I can't seem to find references to this, or consistent documentation on MTU settings. The message Lowering IPv6 MTU (9216) to match device MTU (1500) seems to imply that 9216 is an IPv6-wide setting.

Seeing mentions that the MTU ifcfg settings might be a ceiling (and thus this is the cause of the error), I've also tried setting them all to 9216 with no change in the frequency of errors.

In fact, it seems that 1500 is the limit (even with the change to 9216 in the config scripts):

# echo "1500" > /proc/sys/net/ipv6/conf/wlp3s0/mtu # echo "1501" > /proc/sys/net/ipv6/conf/wlp3s0/mtu   -bash: echo: write error: Invalid argument # echo "1400" > /proc/sys/net/ipv6/conf/wlp3s0/mtu #  

This is on a ThinkPad W540 running Fedora 22:

# uname -a Linux my_machine.my_domain.com 4.4.14-200.fc22.x86_64 #1 SMP Fri Jun 24 21:19:33 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux 

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Category: linux Time: 2016-07-28 Views: 2

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