(RADIATOR) Outgoing traffic IP on multi-homed host

[jlewis at lewis.org]

On Mon, 18 Mar 2002, Hugh Irvine wrote:

> > Does anyone know of a way to get Radiator to respond back on the IP
> > something came in on on a multihomed host, without apparently running a
> > separate copy of radiator bound to each IP address? Or am I just stupid and
> > missing something simple? =)
> >
> > This is with Radiator 2.19 on RH Linux 7.2.
> >
>
> You are correct when you say the only way to do this is by running separate
> instances of Radiator on different IP addresses (and possibly different port
> numbers as well).
>
> The source IP address used for the reply packet is usually determined by the
> operating system, rather than Radiator.

I don't know how the radius protocol might be affected by this, but there
are tricks you can utilize on a Linux system with multiple IPs to cause
outgoing packets to have the source address of your choice.

Suppose you have a system with eth0 10.0.0.10 and a number of IP aliases
on eth0:XX, and a default gw of 10.0.0.1  i.e.

ifconfig eth0 10.0.0.10 ...
ifconfig eth0:0 10.0.0.2 ...
ifconfig eth0:1 10.0.0.3 ...
route add default gw 10.0.0.1

If you want to talk to 10.2.0.1 as 10.0.0.2 and talk to 10.3.0.1 as
10.0.0.3, do the following:

route add -host 10.2.0.1 gw 10.0.0.1 dev eth0:0
route add -host 10.3.0.1 gw 10.0.0.1 dev eth0:1

Packets leaving the system will use the source address of the interface
(or alias interface) you specify in the dev portion of the route.

-- 
----------------------------------------------------------------------
 Jon Lewis *jlewis at lewis.org*|  I route
 System Administrator        |  therefore you are
 Atlantic Net                |
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