Multi-homing

[Weary in West Chester]

Good Afternoon folks, I'm back again. I'm trying to locate some information on Multi-homing to find out what exactly it is / or does. Have you heard of it? What is it or what does it do (in 50 words or less...)? Then, do you have any internet links to sites that publish any good info explaining what it is and how to set it up?

What has to be set up on the UNIX system, anything? Is this something you set up through your ISP? I'm so confused. Any help would be much appreciated. Thanks again in advance:-)

[Martin Burnett]

Multi-homing means that your computer or server has multiple network interface cards (NICs) and each is on a different subnet or network. This allows the server to act as a router or to be accessed by different users on different subnets. It is also used for maintaining multiple web sites with each NIC having a seperate IP address.

[Kofi ARTHIABAH]

When you have a server with multiple network cards each of which is connected to a diffent network, the server is said to be multi-homed. Firewalls (and routers) are good multihome candidates.

From a security standpoint, multihoming your servers (to the internet) is a bad idea (its like having multiple entry points to your house...) From an traffic accounting standpoint, it can be a nightmare to keep a track of.

But if you absolutely have to (for example if you are setting up vpn's with suppliers etc) you would have to define specific routes for traffic destined for particular networks. I would say, leave the multihoming to another device (firewall or router)

[Anthony Goonetilleke]

Hmm 50 words or less (oops thats 10 words already!)
Here goes..
When a machine has two or more physical connections they are called multi-homed hosts. Multihomed hosts require more than one IP address. Each address correponds to one of the machines network connections.
How is that exactly 50 words!

[Edward D. Herring]

A multi-homed computer can also be used as a router. By setting up a static routing table,(enabling IP forwarding on NT) or you could even use RIP.

[Weary in West Chester]

Thank you all for your input. Now here's the next little piece of the puzzle. Can you assign multiple ip addresses to the same NIC card?

[John Palmer]

Yes,

For 10.20 see man ifalias which came with one of the early network patches.

For 11.00 see man ifconfig.
ifconfig lan0 .....
ifconfig lan0:1 ....
etc.

[Anthony Goonetilleke]

Hmm sneaky.. two questions in one (at least this doesnt have the 50 word limit)

ifconfig lan0:0 inet 18.2.2.2
ifconfig lan0:1 inet 18.3.3.3

to make it permanant add the following entries into /etc/rc.comfig.d/netconf

INTERFACE_NAME[0]=lan0
IP_ADDRESS[0]=18.2.2.2
SUBNET_MASK[0]=255.0.0.0
INTERFACE_STATE[0]=up

INTERFACE_NAME[1]=lan0:1
IP_ADDRESS[1]=18.3.3.3
SUBNET_MASK[1]=255.0.0.0
INTERFACE_STATE[1]=up