In my pc under linux Scientific Linux 6.4 I have many ethernet 
interfaces ( managed through Network Manager) eth0 connects to the 
switch, I'm not concerned about that. eth1 used to connect directly to 
another pc. Most of the time I don't use it, and there's nothing plugged 
into it.

The problem is when nothing is plugged into eth1 the ip address 
(192.168.5.1) associated with it is not available, as you can see:

Eth1 plugged:

# ip address show

1: lo: mtu 16436 qdisc noqueue state UNKNOWN link/loopback 
00:00:00:00:00:00 brd 00:00:00:00:00:00 inet 127.0.0.1/8 scope host lo 
inet6 ::1/128 scope host valid_lft forever preferred_lft forever

2: eth0: mtu 1500 qdisc mq state UP qlen 1000 link/ether 
e4:1f:13:e1:55:d8 brd ff:ff:ff:ff:ff:ff inet 192.168.1.12/24 brd 
192.168.1.255 scope global eth0 inet6 fe80::e61f:13ff:fee1:55d8/64 scope 
link valid_lft forever preferred_lft forever

3: eth1: mtu 1500 qdisc mq state UP qlen 1000 link/ether 
e4:1f:13:e1:55:d9 brd ff:ff:ff:ff:ff:ff inet 192.168.5.1/24 brd 
192.168.5.255 scope global eth1 inet6 fe80::e61f:13ff:fee1:55d9/64 scope 
link valid_lft forever preferred_lft forever

Eth1 not plugged: # ip address show

1: lo: mtu 16436 qdisc noqueue state UNKNOWN link/loopback 
00:00:00:00:00:00 brd 00:00:00:00:00:00 inet 127.0.0.1/8 scope host lo 
inet6 ::1/128 scope host valid_lft forever preferred_lft forever

2: eth0: mtu 1500 qdisc mq state UP qlen 1000 link/ether 
e4:1f:13:e1:55:d8 brd ff:ff:ff:ff:ff:ff inet 192.168.1.12/24 brd 
192.168.1.255 scope global eth0 inet6 fe80::e61f:13ff:fee1:55d8/64 scope 
link valid_lft forever preferred_lft forever

3: eth1: mtu 1500 qdisc mq state DOWN qlen 1000 link/ether 
e4:1f:13:e1:55:d9 brd ff:ff:ff:ff:ff:ff inet6 
fe80::e61f:13ff:fee1:55d9/64 scope link valid_lft forever preferred_lft 
forever

How can I get the ip 192.168.5.1 eth1 available even if it is not 
connected (plugged to another pc/switch) ?