There also seems to be another bug for ipv6 only; the sysctl setting of
mtu happens before the ip link set dev up; which means, at up time, the
interface gets the default mtu which clobbers the ipv6 mtu.
/sbin/sysctl -q -e -w net.ipv6.conf.ens8.autoconf=0
/sbin/sysctl -q -e -w net.ipv6.conf.ens8.mtu=1480
/bin/ip link set dev ens8 up
/bin/ip -6 addr add fd0d:ffe0:5771::1:0:0/64 dev ens8
I'm testing this post-up hook which I think covers all of the cases.
# cat /etc/network/if-up.d/mtuipv6
#!/bin/sh
[ "$IFACE" != "lo" ] || exit 0
# Trigger only if MTU configured
[ -n "$IF_MTU" ] || exit 0
# Target ipv6 MTU settings only
[ "$ADDRFAM" = "inet6" ] || exit 0
# We need to check the underlying interface MTU and
# raise it if the IPV6 mtu is larger
CUR_DEV_MTU=$(/bin/cat /sys/class/net/$IFACE/mtu)
if [ $CUR_DEV_MTU -lt $IF_MTU ]; then
/bin/ip link set $IFACE mtu $IF_MTU
fi
/sbin/sysctl -q -e -w net.ipv6.conf.$IFACE.mtu=$IF_MTU
Thoughts?
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https://bugs.launchpad.net/bugs/1609367
Title:
ifupdown does not set ipv6-only large mtu
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