[Linux-users] 2 IP's on the same network card

[David Bandel]

On 8/27/07, James McDonald <james at jamesmcdonald.id.au> wrote:
> Dirk Moolman wrote:
> > Ok, I found it - and it is actually so simple:
> >
> > http://learnlinux.tsf.org.za/courses/build/net-admin/ch01s10.html
> >
> > To plumb your device, you may run the command:
> >
> > ifconfig eth0 192.168.0.1 netmask 255.255.255.0
> > ifconfig eth0:1 172.16.5.1 netmask 255.255.255.0
> >
> >
> > "These commands would plumb the interface. Notice that the eth0:1 gives
> > the interface the second IP address. Using any number in place of the
> > '1' would also work."
> >
> >
> >
> Another lower level way of doing the same thing is using ip
>
> ip addr
>
> 2: eth0: <BROADCAST,MULTICAST,UP,10000> mtu 1500 qdisc pfifo_fast qlen 1000
>     link/ether 00:08:74:3b:59:58 brd ff:ff:ff:ff:ff:ff
>     inet 192.168.1.6/24 brd 192.168.1.255 scope global eth0
>     inet6 fe80::208:74ff:fe3b:5958/64 scope link
>        valid_lft forever preferred_lft forever
>
> ip addr add 192.168.1.220 dev eth0
>    2: eth0: <BROADCAST,MULTICAST,UP,10000> mtu 1500 qdisc pfifo_fast
> qlen 1000
>     link/ether 00:08:74:3b:59:58 brd ff:ff:ff:ff:ff:ff
>     inet 192.168.1.6/24 brd 192.168.1.255 scope global eth0
>     inet 192.168.1.220/32 scope global eth0
>     inet6 fe80::208:74ff:fe3b:5958/64 scope link
>        valid_lft forever preferred_lft forever
>
> To delete
> ip addr del 192.168.1.220 dev eth0
>
> However the secondary address will not show up using ifconfig
> ifconfig
> eth0      Link encap:Ethernet  HWaddr 00:08:74:3B:59:58
>           inet addr:192.168.1.6  Bcast:192.168.1.255  Mask:255.255.255.0
>           inet6 addr: fe80::208:74ff:fe3b:5958/64 Scope:Link
>           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
>           RX packets:4377 errors:0 dropped:0 overruns:0 frame:0
>           TX packets:1777 errors:0 dropped:0 overruns:0 carrier:0
>           collisions:0 txqueuelen:1000
>           RX bytes:1151555 (1.0 MiB)  TX bytes:145992 (142.5 KiB)
>           Interrupt:11 Base address:0x2c00
>

This is actually the better way to do it.  The problem with using
aliases (eth0:1, etc.) is that if you try to down eth0 for any reason,
you will down _all_ aliases as well.  Using the ip method, this
doesn't happen.

Ciao,

David A. Bandel
-- 
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            - Nemesis Air Racing Team motto