Debian (OpenMediaVault) cannot resolve hostnames

Question

Recently I got a new router (Fritz.Box 6490) and had to change the network settings on my NAS. I turned on my debian-wheezy-based-OpenMediaVault-PC and set eth0 up for DHCP by editing /etc/network/interfaces manually (it was fixed to 192.168.0.2 before). The NAS was instantly accessible again on my home network. I then wanted to upgrade my system via an SSH root session from my desk so I gave apt-get update a try and ended up with this error being the same for all sources:

Err http://ftp.de.debian.org wheezy Release.gpg
  On resolving »ftp.de.debian.org:http« something bad happened (-5 - no hostname belong to this address).
// output translated by myself

I noticed that I can't ping my router with ping fritz.box, but when using ping 192.168.178.1 it works fine. Internet access also seems to work fine, since I can even ping google.com with its IP. I guess therefore it won't be a network configuration problem.

What else might be the problem here? I already checked several other things but Linux is not really my strong suit, so I've included a set of outputs below that might help things along.

/etc/network/interfaces:

# The loopback network interface
auto lo
iface lo inet loopback

# eth0 network interface
auto eth0
allow-hotplug eth0
iface eth0 inet dhcp
    pre-down ethtool -s $IFACE wol g
iface eth0 inet6 manual
    pre-down ip -6 addr flush dev $IFACE

route -n:

Ziel            Router          Genmask         Flags Metric Ref    Use Iface
0.0.0.0         192.168.178.1   0.0.0.0         UG    0      0        0 eth0
192.168.178.0   0.0.0.0         255.255.255.0   U     0      0        0 eth0

ifconfig:

eth0      Link encap:Ethernet  Hardware Adresse d0:50:99:76:10:e9
          inet Adresse:192.168.178.27  Bcast:192.168.178.255  Maske:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metrik:1
          RX packets:2929 errors:0 dropped:0 overruns:0 frame:0
          TX packets:2243 errors:0 dropped:0 overruns:0 carrier:0
          Kollisionen:0 Sendewarteschlangenlänge:1000
          RX bytes:607082 (592.8 KiB)  TX bytes:611104 (596.7 KiB)
          Interrupt:136 Basisadresse:0xc000

lo        Link encap:Lokale Schleife
          inet Adresse:127.0.0.1  Maske:255.0.0.0
          inet6-Adresse: ::1/128 Gültigkeitsbereich:Maschine
          UP LOOPBACK RUNNING  MTU:16436  Metrik:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          Kollisionen:0 Sendewarteschlangenlänge:0
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

/etc/apt/sources.list:

# deb cdrom:[Debian GNU/Linux 7.0.0 _Wheezy_ - Official Snapshot amd64 LIVE/INSTALL Binary 20150629-08:52]/ wheezy contrib main non-free
# deb cdrom:[Debian GNU/Linux 7.0.0 _Wheezy_ - Official Snapshot amd64 LIVE/INSTALL Binary 20150629-08:52]/ wheezy contrib main non-free

deb http://ftp.de.debian.org/debian/ wheezy main
deb-src http://ftp.de.debian.org/debian/ wheezy main

deb http://security.debian.org/ wheezy/updates main contrib non-free
deb-src http://security.debian.org/ wheezy/updates main contrib non-free

# wheezy-updates, previously known as 'volatile'
deb http://ftp.de.debian.org/debian/ wheezy-updates main contrib non-free
deb-src http://ftp.de.debian.org/debian/ wheezy-updates main contrib non-free

Solution

Dammit, should've waited 10 minutes longer before asking my question :D

So, the problem was within /etc/resolv.conf the file was still referring to my old network and looked like this:

search local
nameserver 192.168.0.1
nameserver 192.168.0.2

and I changed it to

search local
nameserver 192.168.178.1

Now it works like a charm again. But this still is kinda wierd, because I did try to set the setting to DHCP through the OpenMediaVault web interface after I found out that I cannot resolve hostnames, but this function does not seem to change the data of the resolv.conf file. Anyways.. problem solved ;)