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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?

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1 Answer 1

That nameserver address is being supplied by the DHCP server. 'fd00' is presumably a Unique Local Address prefix, probably set in /etc/radvd.conf on the server. The address gets sent to NetworkManager and dhclient during DHCP negotiation and NetworkManager sends it to resolvconf which puts it in resolv.conf. To change or eliminate that address you need to configure your DHCP server.

This may help: http://rwmj.wordpress.com/2011/06/02/ipv6-lan/

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