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?