Quando você usa:
root@debian:/home/mohsen# ip addr show up
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
valid_lft forever preferred_lft forever
inet6 ::1/128 scope host
valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
link/ether 18:03:73:60:b4:4e brd ff:ff:ff:ff:ff:ff
inet 192.168.1.14/24 brd 192.168.1.255 scope global eth0
valid_lft forever preferred_lft forever
inet 192.168.1.21/24 brd 192.168.1.255 scope global secondary eth0:1
valid_lft forever preferred_lft forever
inet6 fe80::1a03:73ff:fe60:b44e/64 scope link
valid_lft forever preferred_lft forever
Eu configurei alias IP para eth0, voce tem que encontrar IPs de ethernet de set na ethernet dada. Ou você pode usar:
root@debian:/home/mohsen# ifconfig
eth0 Link encap:Ethernet HWaddr 18:03:73:60:b4:4e
inet addr:192.168.1.14 Bcast:192.168.1.255 Mask:255.255.255.0
inet6 addr: fe80::1a03:73ff:fe60:b44e/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:101110 errors:0 dropped:0 overruns:0 frame:0
TX packets:81804 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:89999660 (85.8 MiB) TX bytes:10808197 (10.3 MiB)
eth0:1 Link encap:Ethernet HWaddr 18:03:73:60:b4:4e
inet addr:192.168.1.21 Bcast:192.168.1.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
É melhor não usar o alias IP e usar o IP original.