The ifconfig utility is the tool used to set up and configure your network card. You should understand this command in the event you need to configure the network by hand. An important note to take care with is when using ifconfig to configure your network devices; the settings will not survive a reboot.
To assign the eth0 interface the IP-address of 208.164.186.2 use the command:
[root@deep] /#ifconfig eth0 208.164.186.2 netmask 255.255.255.0
Usually, the pratice is to configure or change the TCP/IP networking manually only to make some test on the server. If you want to keep your TCP/IP values, it's preferable to set them in the files related to networking functionality.
To display all the interfaces you have on your server, use the command:
[root@deep] /#ifconfig
The output should look something like this:
eth0 Link encap:Ethernet HWaddr 00:E0:18:90:1B:56
inet addr:208.164.186.2 Bcast:208.164.186.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:1295 errors:0 dropped:0 overruns:0 frame:0
TX packets:1163 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:100
Interrupt:11 Base address:0xa800
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
UP LOOPBACK RUNNING MTU:3924 Metric:1
RX packets:139 errors:0 dropped:0 overruns:0 frame:0
TX packets:139 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
If the ifconfig tool is invoked without any parameters, it displays all interfaces you have configured. An option of -a shows the inactive one as well.
To display all interfaces as well as inactive interfaces you may have, use the command:
[root@deep] /#ifconfig -a
The output should look something like this:
eth0 Link encap:Ethernet HWaddr 00:E0:18:90:1B:56
inet addr:208.164.186.2 Bcast:208.164.186.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:1295 errors:0 dropped:0 overruns:0 frame:0
TX packets:1163 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:100
Interrupt:11 Base address:0xa800
eth1 Link encap:Ethernet HWaddr 00:E0:18:90:1B:56
inet addr:192.168.1.1 Bcast:192.168.1.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:1295 errors:0 dropped:0 overruns:0 frame:0
TX packets:1163 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:100
Interrupt:5 Base address:0xa320
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
UP LOOPBACK RUNNING MTU:3924 Metric:1
RX packets:139 errors:0 dropped:0 overruns:0 frame:0
TX packets:139 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
It is important to note that the settings configured with the ifconfig toll for your network devices will not survive a reboot.
To assign the default gateway for 208.164.186.12 use the command:
[root@deep] /#route add default gw 208.164.186.1
In this example, the default route is set up to go to 208.164.186.12, your router. Once again, if you want to keep your default gateway value, it's preferable to set in it the files related
to networking functionality -/etc/sysconfig/network.
Verify that you can reach your hosts. Choose a host from your network, for instance 208.164.186.1. Use the command:
[root@deep] /#ping 208.164.186.1
The output should look something like this:
[root@deep networking]# ping 208.164.186.1
PING 208.164.186.1 (208.164.186.1) from 208.164.186.2 : 56 data bytes
64 bytes from 208.164.186.2: icmp_seq=0 ttl=128 time=1.0 ms
64 bytes from 208.164.186.2: icmp_seq=1 ttl=128 time=1.0 ms
64 bytes from 208.164.186.2: icmp_seq=2 ttl=128 time=1.0 ms
64 bytes from 208.164.186.2: icmp_seq=3 ttl=128 time=1.0 ms
--- 208.164.186.1 ping statistics ---
4 packets transmitted, 4 packets received, 0% packet loss
round-trip min/avg/max = 1.0/1.0/1.0 ms
You should now display the routing information with the command route to see if both hosts have the correct routing entry. Use the command:
[root@deep] /#route -n
The output should look something like this:
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
208.164.186.2 0.0.0.0 255.255.255.255 UH 0 0 0 eth0
208.164.186.0 208.164.186.2 255.255.255.0 UG 0 0 0 eth0
208.164.186.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0
127.0.0.0 0.0.0.0 255.0.0.0 U 0 0 0 lo
To check the status of the interfaces quickly, use the netstat -i command, as follows:
[root@deep] /#netstat -i
The output should look something like this:
Kernel Interface table
Iface MTU Met RX-OK RX-ERR RX-DRP RX-OVR TX-OK TX-ERR TX-DRP TX-OVR Flg
eth0 1500 0 4236 0 0 0 3700 0 0 0 BRU
lo 3924 0 13300 0 0 0 13300 0 0 0 LRU
ppp0 1500 0 14 1 0 0 16 0 0 0 PRU
Another useful netstat option is -t, which shows all active TCP connections. Following is a typical result of netstat -t:
[root@deep] /#netstat -t
The output should look something like this:
Active Internet connections (w/o servers)
Proto Recv-Q Send-Q Local Address Foreign Address State
Tcp 0 0 deep.openar:netbios-ssn gate.openna.com:1045 ESTABLISHED
Tcp 0 0 localhost:1032 localhost:1033 ESTABLISHED
Tcp 0 0 localhost:1033 localhost:1032 ESTABLISHED
Tcp 0 0 localhost:1030 localhost:1034 ESTABLISHED
Tcp 0 0 localhost:1031 localhost:1030 ESTABLISHED
Tcp 0 0 localhost:1028 localhost:1029 ESTABLISHED
Tcp 0 0 localhost:1029 localhost:1028 ESTABLISHED
Tcp 0 0 localhost:1026 localhost:1027 ESTABLISHED
Tcp 0 0 localhost:1027 localhost:1026 ESTABLISHED
Tcp 0 0 localhost:1024 localhost:1025 ESTABLISHED
Tcp 0 0 localhost:1025 localhost:1024 ESTABLISHED
To shows all active and listen TCP connections, use the command:
[root@deep] /#netstat -vat
The output should look something like this:
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address Foreign Address State
tcp 0 0 deep.openna.co:domain *:* LISTEN
tcp 0 0 localhost:domain *:* LISTEN
tcp 0 0 deep.openna.com:ssh gate.openna.com:1682 ESTABLISHED
tcp 0 0 *:webcache *:* LISTEN
tcp 0 0 deep.openar:netbios-ssn *:* LISTEN
tcp 0 0 localhost:netbios-ssn *:* LISTEN
tcp 0 0 localhost:1032 localhost:1033 ESTABLISHED
tcp 0 0 localhost:1033 localhost:1032 ESTABLISHED
tcp 0 0 localhost:1030 localhost:1031 ESTABLISHED
tcp 0 0 localhost:1031 localhost:1030 ESTABLISHED
tcp 0 0 localhost:1028 localhost:1029 ESTABLISHED
tcp 0 0 localhost:1029 localhost:1028 ESTABLISHED
tcp 0 0 localhost:1026 localhost:1027 ESTABLISHED
tcp 0 0 localhost:1027 localhost:1026 ESTABLISHED
tcp 0 0 localhost:1024 localhost:1025 ESTABLISHED
tcp 0 0 localhost:1025 localhost:1024 ESTABLISHED
tcp 0 0 deep.openna.com:www *:* LISTEN
tcp 0 0 deep.openna.com:https *:* LISTEN
tcp 0 0 *:389 *:* LISTEN
tcp 0 0 *:ssh *:* LISTEN
To stop all network devices manually on your system, use the following command:
[root@deep] /# /etc/rc.d/init.d/network stop
Shutting down interface eth0 [ OK ]
Disabling IPv4 packet forwarding [ OK ]
To start all network devices manually on your system, use the following command:
[root@deep] /# /etc/rc.d/init.d/network start
Enabling IPv4 packet forwarding [ OK ]
Bringing up interface lo [ OK ]
Bringing up interface eth0 [ OK ]