Why ifconfig command should not be used any more in RHEL7?

Why ifconfig command should not be used any more in RHEL7?

We could see the IP address configured on any network interface using command #ip addr show command.

Here you could see there already IP “192.168.0.12” is configured on network interface “eno16777736”

[root@rhelserver /]# ip addr  show 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 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        valid_lft forever preferred_lft forever     inet6 ::1/128 scope host        valid_lft forever preferred_lft forever 2: eno16777736: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000     link/ether 00:0c:29:3b:3c:a0 brd ff:ff:ff:ff:ff:ff     inet 192.168.0.12/24 brd 192.168.0.255 scope global eno16777736        valid_lft forever preferred_lft forever     inet6 fe80::20c:29ff:fe3b:3ca0/64 scope link        valid_lft forever preferred_lft forever [root@rhelserver /]#

You could check the route information via command #ip route show

[root@rhelserver /]# ip route show default via 192.168.0.1 dev eno16777736  proto static  metric 1024 192.168.0.0/24 dev eno16777736  proto kernel  scope link  src 192.168.0.12

Now I am trying to add one more IP address “10.0.0.10” on interface “eno16777736”.

# ip addr add dev eno16777736 10.0.0.10/24 [root@rhelserver /]# ip addr add dev eno16777736 10.0.0.10/24 [root@rhelserver /]# ip addr show 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 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        valid_lft forever preferred_lft forever     inet6 ::1/128 scope host        valid_lft forever preferred_lft forever 2: eno16777736: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000     link/ether 00:0c:29:3b:3c:a0 brd ff:ff:ff:ff:ff:ff     inet 192.168.0.12/24 brd 192.168.0.255 scope global eno16777736        valid_lft forever preferred_lft forever     inet 10.0.0.10/24 scope global eno16777736        valid_lft forever preferred_lft forever     inet6 fe80::20c:29ff:fe3b:3ca0/64 scope link        valid_lft forever preferred_lft forever

We could see both IP “192.168.0.24” & “10.0.0.10” are configured on interface “eno16777736”

Now let’s use “ifconfig”, as many of us are used to using ifconfig command.

[root@rhelserver /]# ifconfig eno16777736: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500         inet 192.168.0.12  netmask 255.255.255.0  broadcast 192.168.0.255         inet6 fe80::20c:29ff:fe3b:3ca0  prefixlen 64  scopeid 0x20<link>         ether 00:0c:29:3b:3c:a0  txqueuelen 1000  (Ethernet)         RX packets 627  bytes 74074 (72.3 KiB)         RX errors 0  dropped 0  overruns 0  frame 0         TX packets 708  bytes 45361 (44.2 KiB)         TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0 lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536         inet 127.0.0.1  netmask 255.0.0.0         inet6 ::1  prefixlen 128  scopeid 0x10<host>         loop  txqueuelen 0  (Local Loopback)         RX packets 461  bytes 45712 (44.6 KiB)         RX errors 0  dropped 0  overruns 0  frame 0         TX packets 461  bytes 45712 (44.6 KiB)         TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

As you could see, we could see first IP address “192.168.0.12” , but “ifconfig” command has no capabilities of showing other IP address i.e. “10.0.0.24”

Even if you use # ifconfig –a, It will not show the IP address “10.0.0.10”

[root@rhelserver /]# ifconfig -a eno16777736: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500         inet 192.168.0.12  netmask 255.255.255.0  broadcast 192.168.0.255         inet6 fe80::20c:29ff:fe3b:3ca0  prefixlen 64  scopeid 0x20<link>         ether 00:0c:29:3b:3c:a0  txqueuelen 1000  (Ethernet)         RX packets 627  bytes 74074 (72.3 KiB)         RX errors 0  dropped 0  overruns 0  frame 0         TX packets 708  bytes 45361 (44.2 KiB)         TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0 lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536         inet 127.0.0.1  netmask 255.0.0.0         inet6 ::1  prefixlen 128  scopeid 0x10<host>         loop  txqueuelen 0  (Local Loopback)         RX packets 461  bytes 45712 (44.6 KiB)         RX errors 0  dropped 0  overruns 0  frame 0         TX packets 461  bytes 45712 (44.6 KiB)         TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

It would be shocking for many sys admin, who like ifconfig command so much, but the man page of ifconfig command says.

# man ifconfig IFCONFIG(8)                                                                          Linux System Administrator's Manual                                                                          IFCONFIG(8) NAME        ifconfig - configure a network interface SYNOPSIS        ifconfig [-v] [-a] [-s] [interface]        ifconfig [-v] interface [aftype] options | address ... NOTE        This program is obsolete!  For replacement check ip addr and ip link.  For statistics use ip -s link.

So do not use ifconfig command any more, you may miss any network information configured on the network interface.

Thank you for reading.

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