Problems setting up DNS, gateway und subnetmask!

Hi!
I have received from my ISP an IP, DNS, Subnetmask and the DNS Serverentries to add to my ubuntu linux machine

My interfaces File /etc/network/interfaces:
# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).

# The loopback network interface
auto lo
iface lo inet loopback
address 127.0.0.1
netmask 255.0.0.0

# This is a list of hotpluggable network interfaces.
# They will be activated automatically by the hotplug subsystem.
mapping hotplug
script grep
map eth0

# The primary network interface


auto eth0

iface eth0 inet static
address 81.10.53.22
netmask 255.255.255.252
gateway 10.0.0.138
dns-search lan
dns-nameservers 163.121.128.134 212.103.160.18

My File /etc/hosts:

127.0.0.1 localhost.localdomain localhost ubuntu
# The following lines are desirable for IPv6 capable hosts
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
ff02::3 ip6-allhosts

If I enter the command route:

Kernel IP Routentabelle
Ziel Router Genmask Flags Metric Ref Use Iface
81.10.53.20 * 255.255.255.252 U 0 0 0 eth0

If I run explicitly this command to add the gateway to my eth0 interface:


sudo route add default gateway 10.0.0.138 eth0

I receive this errormessage:
SIOCADDRT: Das Netzwerk ist nicht erreichbar (Network unreachable)


For any help solving my problem, thanks in advance

Tamer
.