I have a Red Hat 6 vm created in my VMware Workstation Lab. I will just go ahead and add a new NIC card to my running RHEL machine.
Now let us try to detect it without rebooting the OS
If we check the output of ifconfig
# ifconfig
eth0 Link encap:Ethernet HWaddr 00:0C:29:B9:4D:D3
inet addr:192.168.1.11 Bcast:192.168.1.255 Mask:255.255.255.0
inet6 addr: fe80::20c:29ff:feb9:4dd3/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:91992 errors:0 dropped:0 overruns:0 frame:0
TX packets:58283 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:99437002 (94.8 MiB) TX bytes:5498693 (5.2 MiB)
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:2964 errors:0 dropped:0 overruns:0 frame:0
TX packets:2964 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:388592 (379.4 KiB) TX bytes:388592 (379.4 KiB)So as of now the new thernet card configuration is not reflected. There is a file /etc/udev/rules.d/70-persistent-net.rules which contains details about the connected ethernet card in your RHEL box.
I have discussed about the working of this file in the below link
device eth0 does not seem to be present, delaying initialization
In this file you can view the details of the newly connected Ethernet Card
# PCI device 0x8086:0x100f (e1000)
SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="00:0c:29:b9:4d:d3", ATTR{type}=="1", KERNEL=="eth*", NAME="eth0"
# PCI device 0x8086:0x100f (e1000)
SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="00:0c:29:b9:4d:dd", ATTR{type}=="1", KERNEL=="eth*", NAME="eth1"As you see it shows two ethernet card details i.e. eth0 and eth1. As of now eth0 is already in connected state as per the output of ifconfig which can also match using the MAC details. So let us manually create a new configuration file for the new card.
# cd /etc/sysconfig/network-scriptsTo skip the hard work let us copy the contents from eth0 to our new file, in that way we will just have to make required changes
# cp ifcfg-eth0 ifcfg-eth1Lines marked in blue are the one you need to change as per your environment
# vi ifcfg-eth1
DEVICE=eth1
TYPE=Ethernet
ONBOOT=yes
NM_CONTROLLED=no
BOOTPROTO=none
HWADDR=00:0c:29:b9:4d:dd
IPADDR=192.168.1.5
PREFIX=24
GATEWAY=192.168.1.1
DNS1=8.8.8.8
DEFROUTE=yes
IPV4_FAILURE_FATAL=yes
IPV6INIT=no
NAME="System eth1"Restart your network services
# service network restart
Shutting down interface eth0: [ OK ]
Shutting down loopback interface: [ OK ]
Bringing up loopback interface: [ OK ]
Bringing up interface eth0: Determining if ip address 192.168.1.11 is already in use for device eth0...
[ OK ]
Bringing up interface eth1: Determining if ip address 192.168.1.5 is already in use for device eth1...
[ OK ]Verify your results
# ifconfig
eth0 Link encap:Ethernet HWaddr 00:0C:29:B9:4D:D3
inet addr:192.168.1.11 Bcast:192.168.1.255 Mask:255.255.255.0
inet6 addr: fe80::20c:29ff:feb9:4dd3/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:92368 errors:0 dropped:0 overruns:0 frame:0
TX packets:58550 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:99470396 (94.8 MiB) TX bytes:5531059 (5.2 MiB)
eth1 Link encap:Ethernet HWaddr 00:0C:29:B9:4D:DD
inet addr:192.168.1.5 Bcast:192.168.1.255 Mask:255.255.255.0
inet6 addr: fe80::20c:29ff:feb9:4ddd/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:3 errors:0 dropped:0 overruns:0 frame:0
TX packets:10 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:372 (372.0 b) TX bytes:636 (636.0 b)
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:2964 errors:0 dropped:0 overruns:0 frame:0
TX packets:2964 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:388592 (379.4 KiB) TX bytes:388592 (379.4 KiB)I hope that was helpful. Let me know your success and failures
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