> I understand this scenario; however, what I don't understand is why
> if we're setting mtu 9002 on the underlying devices, why the mtu on the
> "virtual" device (bond0)
> matters vs. the mtu setting of the ipv6 link, especially since this is ipv6
> only.
I think the slave interface mtu will be used.
> I'm testing this post-up hook which I think covers all of the cases.
yep that script looks good.
only thing i can think of is, what if an interface's inet6 section is
specified (and setup) first, before the interface's inet section? e.g.
auto eth0
iface eth0 inet6 static
address 2001:dbe::1/64
mtu 1480
iface eth0 inet static
address 10.0.0.1
mtu 1500
would that cause the device mtu to be (re)set to 1500, after the ipv6
mtu had been set? That would reset the ipv6 mtu to 1500. Can the
ordering of inet/inet6 sections always be inet before inet6?
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https://bugs.launchpad.net/bugs/1609367
Title:
ifupdown does not set ipv6-only large mtu
Status in ifupdown package in Ubuntu:
Incomplete
Bug description:
ifupdown changes a device's mtu differently, between "inet" section
mtu and "inet6" section mtu. For "inet", ifupdown changes the
device's mtu, using 'ip link set DEV mtu NNN'. However for "inet6",
ifupdown changes the interface's IPv6 mtu, using 'sysctl -q -e -w
net.ipv6.conf.DEV.mtu=NNN'.
The problem is that a device's ipv6 mtu cannot be larger than the
device mtu. Normally this is not a problem; the main reason a device
needs a separate ipv6 mtu is to support ipv6 tunneling inside ipv4
(e.g. 6in4 or 6rd), so ifupdown would also have a ipv4 "inet" section
that contained a larger mtu (or, the ipv6 section would have a lower-
than-default mtu).
But, in the case of an interface that is configured only for ipv6
*and* large frames (e.g. 9000 mtu), there is only an "inet6" section
in the ifupdown config, and so ifupdown fails to set the device's mtu,
which causes its attempt to set the ipv6 mtu to fail.
I believe the correct behavior is for ifupdown to check if there is
any "inet" config section for the same device as the "inet6" section,
and if there is not then it should change the device mtu as well as
the ipv6 mtu. Additionally, the "inet6" configuration must be done
after the "inet" configuration for the same device, since the ipv6 mtu
can't be higher than the device mtu.
I don't see any easy way to add that logic to inet6.defn, however...
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