For anyone reading this because the isc-dhcp-client update broke their
DHCPv6 network:
First, I assume you're running a DHCPv6 server to provide the ipv6
addresses to your clients. If you do not have any Router Advertisement
service configured on your server, the easiest thing to do is use radvd.
# sudo apt install radvd
radvd requires ipv6 forwarding to be enabled (on the server), which you
likely already have enabled, but if not you should edit /etc/sysctl.conf
to uncomment/add:
net.ipv6.conf.all.forwarding=1
then create a /etc/radvd.conf file with contents similar to this,
replacing IFACE with the interface name and using the appropriate ipv6
prefix/len for your network:
interface IFACE # your interface name
{
AdvSendAdvert on; # send RA's on this interface
AdvManagedFlag on; # clients will request DHCPv6 addr
AdvOtherConfigFlag on; # clients will use DHCPv6 other config
AdvDefaultLifetime 0; # this server is NOT a default router (gateway)
prefix 2001:db8::/64 # your subnet prefix/len
{
AdvOnLink on; # everyone in this subnet is "on (this) link"
AdvAutonomous off; # clients will NOT use SLAAC (RFC 4862) addrs
};
};
You can of course leave the # comments out. Then (re)start the radvd
daemon, or just reboot the server.
For comparision, here is an interface before the isc-dhcp-client update,
without any RA:
ubuntu@lp1609898-xenial:~$ ip addr show ens7
3: ens7: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP
group default qlen 1000
link/ether 52:54:00:5f:c4:ee brd ff:ff:ff:ff:ff:ff
inet6 2001:db8::55/64 scope global
valid_lft forever preferred_lft forever
inet6 fe80::5054:ff:fe5f:c4ee/64 scope link
valid_lft forever preferred_lft forever
ubuntu@lp1609898-xenial:~$ ip -6 route
2001:db8::/64 dev ens7 proto kernel metric 256 pref medium
fe80::/64 dev ens7 proto kernel metric 256 pref medium
and after the update, with RA (radvd configured with above conf):
ubuntu@lp1609898-xenial:~$ ip addr show ens7
3: ens7: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP
group default qlen 1000
link/ether 52:54:00:5f:c4:ee brd ff:ff:ff:ff:ff:ff
inet6 2001:db8::55/128 scope global
valid_lft forever preferred_lft forever
inet6 fe80::5054:ff:fe5f:c4ee/64 scope link
valid_lft forever preferred_lft forever
ubuntu@lp1609898-xenial:~$ ip -6 route
2001:db8::55 dev ens7 proto kernel metric 256 pref medium
2001:db8::/64 dev ens7 proto kernel metric 256 expires 86389sec pref medium
fe80::/64 dev ens7 proto kernel metric 256 pref medium
I tested on both xenial and trusty.
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https://bugs.launchpad.net/bugs/1609898
Title:
dhclient incorrectly assumes a /64 ipv6 prefix
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