My /etc/resolv.conf constantly get a mysterious entry, i run a home network with ipv6 provided by ravd, the interface is auto-configured by Network manager (all name server lookups are lost when this line is first in my /etc/resolv.conf) .

Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
**# DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN**
nameserver fd00::1
nameserver 192.168.1.1
search home.int
When ping is working
cat /etc/resolv.conf
# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
# DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN
nameserver 192.168.1.1
search home.int

So something is putting fd00::1 at start of file, not if I ping6 fd00::1 I get Destination unreachable: Administratively prohibited

To diagnose this I ran the router with single cable to connected to ubuntu machine. Ran tcpdump + restarted network on ubuntu. "tcpdump ip6 -e -i eth0 | grep fd00" finds nothing, it's not being advertised via the network..

The only hit I got was when an upstream router refused a connection attempt from the ubuntu machine to fd00::1.

I have also switched on debug for network manager & it appears to set the mystery line..

15:22:14 storage-pc NetworkManager[349]: <info> Activation (eth0) Stage 5 of 5 (IPv4 Commit) complete.
15:22:14 storage-pc NetworkManager[349]: <warn> dnsmasq exited with error: Other problem (5)
15:22:14 storage-pc NetworkManager[349]: <debug> [1346822534.281528] [nm-dns-manager.c:598] update_dns(): updating resolv.conf
15:22:14 storage-pc NetworkManager[349]: <debug> [1346822534.281875] [nm-dns-manager.c:719] update_dns(): DNS: plugin dnsmasq ignored (caching disabled)
15:22:14 storage-pc NetworkManager[349]: <info> ((null)): writing resolv.conf to /sbin/resolvconf
15:22:14 storage-pc dbus[2184]: [system] Successfully activated service 'org.freedesktop.nm_dispatcher'
15:22:14 storage-pc dnsmasq[2875]: reading /etc/resolv.conf
15:22:14 storage-pc dnsmasq[2875]: using nameserver 192.168.1.1#53
15:22:14 storage-pc dnsmasq[2875]: using nameserver fd00::1#53

Any suggestions on how to find out where this comes from?