[Sussex] Virtual IPing?

[Ronan Chilvers]

Hi Paul

On Sat, 15 Apr 2006 10:36:59 +0100 (BST)
paul.morriss at tokenbay.co.uk wrote:

> Hi All
>   I have been told that it's possible to several Linux boxes to have
> the same IP address (e.g. 3 boxes with 192.168.1.100) which act as a
> form of 'load balancing' - the person thought it was called Virtual IP
> addressing??

Don't think you can have more than one machine with the same IP -
doesn't that kinda defeat the object of IP addressing?  You can
certainly have several NICs sharing an IP address in one machine - in
the linux world this is called ethernet bonding.  You can also do
the opposite and have the same NIC bound to several IPs.  Virtual IP (I
think) usually refers to having a virtual interface (such as a bonded
interface) that acts on top of one or more physical interfaces.

Load balancing is usually achieved either by having a dedicated load
balancer in front of the servers (I think there's software out there
to do this with a linux box), or by doing a round robin DNS approach
where you set up several IPs with the same FQDN.  The round robin
approach relies on the fact that a resolution request for the FQDN will
result in one of the possible answers being returned at random which,
over time, gives you load balanced services.

Hope that helps a little??

Cheers
-- 
Ronan
e: ronan at thelittledot.com
t: 01903 739 997

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