How to configure LAN IP in the case of unplugged network cable

# /usr/sbin/ethtool eth0

...

Link detected: no

/etc/sysconfig/network/ifcfg-eth*

LINK_REQUIRED='no'

# cat /etc/sysconfig/network/ifcfg-eth0
BOOTPROTO='static'
BROADCAST=''
ETHTOOL_OPTIONS=''
IPADDR='192.168.28.50/24'
MTU=''
NAME='82545EM Gigabit Ethernet Controller (Copper)'
NETWORK=''
REMOTE_IPADDR=''
STARTMODE='auto'

# rcnetwork restart

# ip a
 eth0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc pfifo_fast state DOWN group default qlen 1000
    link/ether 00:0c:29:fc:16:bb brd ff:ff:ff:ff:ff:ff

# ifconfig 
eth0      Link encap:Ethernet  HWaddr 00# rcnetwork restart

# ip a
 eth0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc pfifo_fast state DOWN group default qlen 1000
    link/ether 00:0c:29:fc:16:bb brd ff:ff:ff:ff:ff:ff

# ifconfig 
eth0      Link encap:Ethernet  HWaddr 00:0C:29:FC:16:BB  
          UP BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:20952 errors:0 dropped:0 overruns:0 frame:0
          TX packets:69999 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:2211956 (2.1 Mb)  TX bytes:5297841 (5.0 Mb):0C:29:FC:16:BB  
          UP BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:20952 errors:0 dropped:0 overruns:0 frame:0
          TX packets:69999 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:2211956 (2.1 Mb)  TX bytes:5297841 (5.0 Mb)

The network cable is disconnected, or the network cable is unplugged.

Starting with SUSE Linux Enterprise Server 12, network services are controlled by the wicked daemon, and the network interface will activate it's configured TCP/IP address only when a link is detected.  

This is different from the same behavior on SUSE Linux Enterprise Server 11.

From the man page :
 

# man 5 ifcfg

       LINK_REQUIRED { auto | yes | no }

              While a working and connected link is required for further setup steps, such as bridge STP, link authentication, auto configuration of the IP address (dhcp,  ...)  and  duplicate  IP  address

              detection  (enabled  by default), it is required in some cases to continue the setup without to consider the link detection (carrier), e.g.  in well-known static "router like" setups. You may

              want to disable also the duplicate IP detection (see CHECK_DUPLICATE_IP and the ifsysctl(5) manual page).



              This variable permits to configure the waiting for link-detection.  When set to yes, wicked waits until link has been detected before it continues with further steps.  When set to no,  wicked

              is  permitted  to  continue  earlier,  without to wait for a link in a usable state.  When set to auto (default), an internal logic is applied causing to use a "no" for tun/tap devices (which

              require a driver daemon) and for bridges with enabled STP and without any ports.  In other cases, it behaves as "yes".