Package: ifupdown
Version: 0.7.53.1
Severity: normal
Tags: ipv6
Dear Maintainer,
When setting the MTU in a inet6 static section in interfaces the MTU is set
on the interface applying to all protocols rather than specific for IPv6.
Steps to reproduce:
1. Add the following option to the 'iface eth0 inet6 static' section in
interfaces:
mtu 1480
2. Reboot
Expected result:
The MTU is set to 1480 for the IPv6 protocol on the specified interface using
a command similar to:
sysctl net.ipv6.conf.eth0.mtu=1480
This is the behaviour when using 'auto' rather than 'static' and the RA
contains an 'AdvLinkMTU' field.
Actual:
The MTU of the interface (eth0) is changed.
This causes the MTU of all protocols, including IPv4 to be set to 1480, which
was not my intention.
This scenario is quiet common when using tunnels (e.g. Sixxs) to provide IPv6
connectivity. My IPv6 MTU needs to be 20 bytes smaller than may IPv4 MTU
because of the tunnel's overhead.
I do realize that changes to this logic might cause existing configurations,
which rely on this behaviour, to break. However it would be really nice if
the behaviour in both 'static' and 'auto' is consistent. Or at least if the
difference is explicitly documented in the man page.
Laurens
-- System Information:
Debian Release: 8.2
APT prefers stable-updates
APT policy: (500, 'stable-updates'), (500, 'stable')
Architecture: amd64 (x86_64)
Kernel: Linux 3.16.0-4-amd64 (SMP w/4 CPU cores)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)
Versions of packages ifupdown depends on:
ii adduser 3.113+nmu3
ii initscripts 2.88dsf-59
ii iproute 1:3.16.0-2
ii iproute2 3.16.0-2
ii libc6 2.19-18+deb8u1
ii lsb-base 4.1+Debian13+nmu1
Versions of packages ifupdown recommends:
ii isc-dhcp-client [dhcp-client] 4.3.1-6
Versions of packages ifupdown suggests:
ii net-tools 1.60-26+b1
pn ppp <none>
pn rdnssd <none>
-- no debconf information
