While the ifconfig command is still available and useful on most if not all Unix/Linux systems today, it is now deprecated on many Linux distributions. That word, which doesn't appear to be popularly used in any context other than in reference to Unix commands, simply means that the command has lost favor and will eventually be phased out -- though not necessarily any time soon. The command that has taken ifconfig's place is ip. While the ip command has numerous options and is considered more powerful than ifconfig, the ip commands you are likely to use are not difficult to learn or remember. There's just a lot more of them.
To see the same type of information that ifconfig will show you, the command to use is ip addr. In this example, the system is using a bonded interface, basically allowing it to aggregate multiple NICs to achieve a higher data rate. The interface to pay attention to is, therefore, the bond0 interface.
$ ip addr 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436 qdisc noqueue 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: <BROADCAST,MULTICAST,SLAVE,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master bond0 qlen 1000 link/ether 63:2b:da:5f:a9:37 brd ff:ff:ff:ff:ff:ff 3: eth1: <BROADCAST,MULTICAST,SLAVE,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master bond0 qlen 1000 link/ether 63:2b:da:5f:a9:37 brd ff:ff:ff:ff:ff:ff 4: sit0: <NOARP> mtu 1480 qdisc noop link/sit 0.0.0.0 brd 0.0.0.0 5: bond0: <BROADCAST,MULTICAST,MASTER,UP,LOWER_UP> mtu 1500 qdisc noqueue link/ether 63:2b:da:5f:a9:37 brd ff:ff:ff:ff:ff:ff inet 10.1.2.155/16 brd 10.1.255.255 scope global bond0 inet6 fe80::7a2b:daff:fe5f:a937/64 scope link valid_lft forever preferred_lft forever
The ifconfig output on this same system would look like this:
$ ifconfig bond0 Link encap:Ethernet HWaddr 63:2B:da:5F:A9:37 inet addr:10.1.2.155 Bcast:10.1.255.255 Mask:255.255.0.0 inet6 addr: fe80::7a2b:daff:fe5f:a937/64 Scope:Link UP BROADCAST RUNNING MASTER MULTICAST MTU:1500 Metric:1 RX packets:632524272 errors:0 dropped:133387 overruns:0 frame:0 TX packets:763888940 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:375990796437 (350.1 GiB) TX bytes:889653824737 (828.5 GiB) eth0 Link encap:Ethernet HWaddr 63:2B:da:5F:A9:37 UP BROADCAST RUNNING SLAVE MULTICAST MTU:1500 Metric:1 RX packets:640963722 errors:0 dropped:133387 overruns:0 frame:0 TX packets:763888940 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:360837640935 (336.0 GiB) TX bytes:889653824737 (828.5 GiB) Interrupt:106 Memory:d2000000-d2012100 eth1 Link encap:Ethernet HWaddr 63:2B:da:5F:A9:37 UP BROADCAST RUNNING SLAVE MULTICAST MTU:1500 Metric:1 RX packets:141560550 errors:0 dropped:0 overruns:0 frame:0 TX packets:0 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:15141155502 (14.1 GiB) TX bytes:0 (0.0 b) Interrupt:114 Memory:d4000000-d4012100 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:866191523 errors:0 dropped:0 overruns:0 frame:0 TX packets:866191523 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:267275935761 (248.9 GiB) TX bytes:267275935761 (248.9 GiB)
Once you get comfortable with the ip addr command, you might prefer to abbreviate it to ip a. And, if you just want to see only the IPv4 or the IPv6 information, you can add an option and use the command ip -4 a or ip -6 a, limiting command's the output to one or the other. You can also limit the command's response to a particular interface by using a command such as ip a show bond0.
$ ip a show bond0 9: bond0: <BROADCAST,MULTICAST,MASTER,UP,LOWER_UP> mtu 1500 qdisc noqueue link/ether 63:2b:da:5f:a9:37 brd ff:ff:ff:ff:ff:ff inet 10.1.2.155/16 brd 10.1.255.255 scope global bond0 inet6 fe80::7a2b:daff:fe5f:a937/64 scope link valid_lft forever preferred_lft forever
As you can see, much of the information provided by the ip command is the same as what you'd see with ifconfig -- the IP and MAC addresses, and the "UP" indicator showing that the interfaces are working. The ip link or ip l command shows a briefer display, but does not include the
$ ip link 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436 qdisc noqueue link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00 2: eth0: <BROADCAST,MULTICAST,SLAVE,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master bond0 qlen 1000 link/ether 63:2b:da:5f:a9:37 brd ff:ff:ff:ff:ff:ff 3: eth1: <BROADCAST,MULTICAST,SLAVE,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master bond0 qlen 1000 link/ether 63:2b:da:5f:a9:37 brd ff:ff:ff:ff:ff:ff 4: sit0: <NOARP> mtu 1480 qdisc noop link/sit 0.0.0.0 brd 0.0.0.0 5: bond0: <BROADCAST,MULTICAST,MASTER,UP,LOWER_UP> mtu 1500 qdisc noqueue link/ether 63:2b:da:5f:a9:37 brd ff:ff:ff:ff:ff:ff
You can use the ip route command to display your routing tables, much like you would see using netstat -r.
$ ip route 10.1.0.0/16 dev bond0 proto kernel scope link src 10.1.2.155 169.254.0.0/16 dev bond0 scope link default via 10.1.1.1 dev bond0 $ $ netstat -r Kernel IP routing table Destination Gateway Genmask Flags MSS Window irtt Iface 10.1.0.0 * 255.255.0.0 U 0 0 0 bond0 169.254.0.0 * 255.255.0.0 U 0 0 0 bond0 default 10.1.1.1 0.0.0.0 UG 0 0 0 bond0
And, as you might have suspected, you can use an abbreivation for the ip route command as well:
$ ip r 10.1.0.0/16 dev bond0 proto kernel scope link src 10.1.2.155 169.254.0.0/16 dev bond0 scope link default via 10.1.1.1 dev bond0
The ip n show command ("n" for "neighbor") displays the kind of network information you would expect to see with a command such as arp -a. In other words, it shows information about other systems that have recently connected to your system. You can also use ip n ls.
$ ip n show 10.1.1.22 dev bond0 lladdr 00:50:56:b1:48:51 STALE 10.1.1.1 dev bond0 lladdr 00:00:0c:07:ac:01 STALE 10.1.4.21 dev bond0 lladdr 00:21:70:bd:30:2e REACHABLE 10.1.1.7 dev bond0 lladdr 08:00:37:bc:a1:6a STALE 10.1.1.8 dev bond0 lladdr 00:50:56:b1:5a:d8 STALE 10.1.4.123 dev bond0 lladdr 00:26:b9:e9:f6:0d STALE 10.1.1.250 dev bond0 lladdr 00:50:56:b1:50:9d DELAY 10.1.1.180 dev bond0 lladdr 00:0b:cd:fe:fd:8d REACHABLE 10.1.2.115 dev bond0 lladdr 08:00:37:da:17:5c REACHABLE $ $ arp -a mon-1.mynet.com (10.1.1.11) at 00:50:56:B1:48:51 [ether] on bond0 ? (10.1.1.1) at 00:00:0C:07:AC:01 [ether] on bond0 ? (10.1.4.23) at 00:21:70:BD:30:2E [ether] on bond0 ? (10.1.1.70) at 08:00:37:BC:A1:6A [ether] on bond0 mon-1.mynet.com (10.1.1.5) at 00:50:56:B1:5A:D8 [ether] on bond0 ? (10.1.4.113) at 00:26:B9:E9:F6:0D [ether] on bond0 all-log-1 (10.1.1.212) at 00:50:56:C2:50:9A [ether] on bond0 mon-1.mynet.com (10.1.1.123) at 00:0B:CD:FE:FD:8D [ether] on bond0 ? (10.1.2.115) at 08:00:37:da:17:5C [ether] on bond0
The state of each neighbor is shown at the end of each line in the ip n show output. The possible states include:
delay -- waiting confirmation failed -- resolution has failed incomplete -- in the process of resolution noarp -- valid, removable when lifetime expires none -- void permanent -- can only be removed administratively probe -- delay timer expired, but no confirmation reachable -- valid until reachability timeout expires stale -- valid but maybe already unreachable
Other useful networking commands include a couple netstat favorites. The netstat -i command will show you network statistics by interface:
$ netstat -i Kernel Interface table Iface MTU Met RX-OK RX-ERR RX-DRP RX-OVR TX-OK TX-ERR TX-DRP TX-OVR Flg bond0 1500 0 632684318 0 133387 0 763890286 0 0 0 BMmRU eth0 1500 0 641044153 0 133387 0 763890286 0 0 0 BMsRU eth1 1500 0 141640165 0 0 0 0 0 0 0 BMsRU lo 16436 0 866250551 0 0 0 866250551 0 0 0 LRU
For per protocol statistics, use the netstat -s command ("s" for "statistics"). This command provides very detailed network information -- likely more than you will need to look at very often, but extremely useful for heavy duty troubleshooting.
$ netstat -s Ip: 1744690691 total packets received 2559835 with invalid addresses 0 forwarded 0 incoming packets discarded 1700771884 incoming packets delivered 1175883101 requests sent out 7068 reassemblies required 3524 packets reassembled ok Icmp: 279076 ICMP messages received 1099 input ICMP message failed. ICMP input histogram: destination unreachable: 4233 timeout in transit: 108 echo requests: 272761 echo replies: 1974 281380 ICMP messages sent 0 ICMP messages failed ICMP output histogram: destination unreachable: 5198 echo request: 3421 echo replies: 272761 IcmpMsg: InType0: 1974 InType3: 4233 InType8: 272761 InType11: 108 OutType0: 272761 OutType3: 5198 OutType8: 3421 Tcp: 9713305 active connections openings 6346380 passive connection openings 2975552 failed connection attempts 3438243 connection resets received 45 connections established 1630650812 segments received 1172423736 segments send out 2826779 segments retransmited 0 bad segments received. 3928370 resets sent Udp: 69839443 packets received 919 packets to unknown port received. 0 packet receive errors 350238 packets sent TcpExt: 120 invalid SYN cookies received 323 resets received for embryonic SYN_RECV sockets 32 packets pruned from receive queue because of socket buffer overrun 33 ICMP packets dropped because they were out-of-window 4343758 TCP sockets finished time wait in fast timer 4834 time wait sockets recycled by time stamp 12 packets rejects in established connections because of timestamp 16658045 delayed acks sent 1292 delayed acks further delayed because of locked socket Quick ack mode was activated 59694 times 2059 times the listen queue of a socket overflowed 2059 SYNs to LISTEN sockets ignored 705660774 packets directly queued to recvmsg prequeue. 100560858 packets directly received from backlog 2061379123 packets directly received from prequeue 254869153 packets header predicted 635912715 packets header predicted and directly queued to user 77257282 acknowledgments not containing data received 1108616005 predicted acknowledgments 285936 times recovered from packet loss due to SACK data Detected reordering 159 times using FACK Detected reordering 46695 times using SACK Detected reordering 19 times using time stamp 19 congestion windows fully recovered 1473 congestion windows partially recovered using Hoe heuristic TCPDSACKUndo: 169 8426 congestion windows recovered after partial ack 18907635 TCP data loss events TCPLostRetransmit: 1907 608 timeouts after SACK recovery 50 timeouts in loss state 2370237 fast retransmits 279757 forward retransmits 26643 retransmits in slow start 14340 other TCP timeouts 1858 sack retransmits failed 3 times receiver scheduled too late for direct processing 7154 packets collapsed in receive queue due to low socket buffer 59861 DSACKs sent for old packets 29977 DSACKs received 48462 DSACKs for out of order packets received 463844 connections reset due to unexpected data 1039018 connections reset due to early user close 3187 connections aborted due to timeout IpExt: InMcastPkts: 1466685 OutMcastPkts: 18093 InBcastPkts: 72565731 OutBcastPkts: 41363
Wrap up: You'll probably be comfortable with using ip commands long before ifconfig disappears from your servers, but why wait? Even people like me who have been typing ifconfig for decades can learn some new tricks