A simple IPv6 setup


Sven Vermeulen Mon 20 May 2013

For internal communication between guests on my workstation, I use IPv6 which is set up using the Router Advertisement "feature" of IPv6. The tools I use are dnsmasq for DNS/DHCP and router advertisement support, and dhcpcd as client. It might be a total mess (grew almost organically until it worked), but as far as I'm concerned, it is working... and that is all that matters (for now). I'll have to look deeper into the IPv6 stuff to understand it all better though.

On the client side, dhcpcd is ran with the following options:

dhcpcd_eth0="-t 5 -L --ipv6ra_own"

I had to enable --ipv6ra_own to get it to obtain its global address, otherwise it only got its link local one (fe80:: something). I also added a hook into /lib/dhcpcd/dhcpcd-hooks to get it to trigger a hostname update for IPv6.

$ cat 28-set-ip6-address 
if $ifup; then export new_ip_address=${ra1_prefix%%/64}; fi

SELinux-policy wise, I had to enable dhcpc_t to write to the hostname proc file and set the system hostname. The first one (21) is needed because of the --ipv6ra_own parameter.

# selocal -l | grep dhcpc_t
21: allow dhcpc_t self:rawip_socket create_socket_perms; # dhcpclient
22: kernel_rw_kernel_sysctl(dhcpc_t) # set hostname
23: allow dhcpc_t self:capability sys_admin; # set hostname

Finally, in /etc/dhcpcd.conf, I removed the nohook lookup-hostname and set the force_hostname one:

#nohook lookup-hostname
env force_hostname=YES

On the server side, I use the following configuration of dnsmasq (snippet):


As you can see, I use the documentation prefix for now (since it is meant for internal communication only, and makes it easier to copy/paste into documentation ;-) but when I am going to use full IPv6 access to the Internet, this prefix will of course change.

Finally, I enabled IPv6 forwarding on the tap0 interface because otherwise I continuously got the following messages on the clients:

May 12 18:43:07 test dhcpcd[3869]: eth0: adding default route via fe80::d848:19ff:fe0d:55c2
May 12 18:43:07 test dhcpcd[3869]: eth0: fe80::d848:19ff:fe0d:55c2 is no longer a router
May 12 18:43:07 test dhcpcd[3869]: eth0: deleting default route via fe80::d848:19ff:fe0d:55c2
May 12 18:43:13 test dhcpcd[3869]: eth0: fe80::d848:19ff:fe0d:55c2 is unreachable, expiring it

To enable IPv6 forwarding, you can use sysctl but I added it in the script that sets up the tap0 interface:

tunctl -b -u swift -t tap0
ifconfig tap0 add 2001:db8:81:e2::26b5:365b:5072/64
vde_switch --numports 16 --mod 777 --group users --tap tap0 -d
echo 1 > /proc/sys/net/ipv6/conf/tap0/forwarding