Public bug reported:
The default route cannot be provided via DHCPv6, it must be obtained
from router advertisements. However, when using the dhcp method for
inet6 in /etc/network/interfaces (e.g. "iface eth0 inet6 dhcp"), ifup
will set net.ipv6.conf.<IFACE>.accept_ra=0, resulting in no default
route for IPv6. Instead, it should explicitly set accept_ra=1.
A workaround is to set it in a post-up script. However, Linux apparently
only sends router solicitations when the interface is brought up, so if
unsolicited RA:s are infrequent the host will be without a default route
until the next RA. This can be worked around by "blinking" the interface
down-up.
Another problem is that when bringing the interface down on dual-stack
hosts, there will be a long timeout. This is because bringing down IPv4
also brings the interface link down, and afterwards dhclient cannot
release the DHCPv6 lease due to the link being down ("RTNETLINK answers:
Cannot assign requested address"). The workaround is to bring the link
back up before bringing IPv6 down.
So the workarounds (which obviously should not be needed) for a dual-
stack dhcp client look like this:
iface eth0 inet dhcp
iface eth0 inet6 dhcp
up sysctl net.ipv6.conf.$IFACE.accept_ra=1
up ip link set dev $IFACE down
up ip link set dev $IFACE up
pre-down ip link set dev $IFACE up
** Affects: ifupdown (Ubuntu)
Importance: Undecided
Status: New
** Tags: ipv6
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https://bugs.launchpad.net/bugs/1013597
Title:
No default route for stateful DHCPv6
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