Network IP aliasing

Assign more than one IP address to one ethernet card:

ifconfig eth0 XXX.XXX.XXX.XXX netmask 255.255.255.0 broadcast XXX.XXX.XXX.255
ifconfig eth0:0 192.168.10.12 netmask 255.255.255.0 broadcast 192.168.10.255
ifconfig eth0:1 192.168.10.14 netmask 255.255.255.0 broadcast 192.168.10.255

route add -host XXX.XXX.XXX.XXX dev eth0
route add -host 192.168.10.12 dev eth0
route add -host 192.168.10.14 dev eth0

In this example 0 and 1 are aliases in addition to the regular eth0. The result of the ifconfig command:

eth0 Link encap:Ethernet HWaddr 00:10:4C:25:7A:3F
inet addr:XXX.XXX.XXX.XXX Bcast:XXX.XXX.XXX.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:14218 errors:0 dropped:0 overruns:0 frame:0
TX packets:1362 errors:0 dropped:0 overruns:0 carrier:0
collisions:1 txqueuelen:100
Interrupt:5 Base address:0xe400

eth0:0 Link encap:Ethernet HWaddr 00:10:4C:25:7A:3F
inet addr:192.168.10.12 Bcast:192.168.10.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
Interrupt:5 Base address:0xe400

eth0:1 Link encap:Ethernet HWaddr 00:10:4C:25:7A:3F
inet addr:192.168.10.14 Bcast:192.168.10.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
Interrupt:5 Base address:0xe400

Config file: /etc/sysconfig/network-scripts/ifcfg-eth0:0

DEVICE=eth0:0
ONBOOT=yes
BOOTPROTO=static
BROADCAST=192.168.10.255
IPADDR=192.168.10.12
NETMASK=255.255.255.0
NETWORK=192.168.10.0
ONBOOT=yes

Aliases can also be shut down independently. i.e.: ifdown eth0:0

The option during kernel compile is: CONFIG_IP_ALIAS=y (Enabled by default in Redhat)

Note: The Apache web server can be configured so that different IP addresses can be assigned to specific domains being hosted. See Apache configuration and "configuring an IP based virtual host" in the YoLinux Web site configuration tutorial.

DHCP Linux Client: get connection info: /sbin/pump -i eth0 --status
(Red Hat Linux 7.1 and older)

Device eth0
IP: 4.XXX.XXX.XXX
Netmask: 255.255.252.0
Broadcast: 4.XXX.XXX.255
Network: 4.XXX.XXX.0
Boot server 131.XXX.XXX.4
Next server 0.0.0.0
Gateway: 4.XXX.XXX.1
Domain: vz.dsl.genuity.net
Nameservers: 4.XXX.XXX.1 4.XXX.XXX.2 4.XXX.XXX.3
Renewal time: Sat Aug 11 08:28:55 2001
Expiration time: Sat Aug 11 11:28:55 2001