[H-GEN] Re: Unix vs NT (religious war :-)

[Michael Anthon]

(Note reply-to: being general at humbug.org.au vs Michael Anthon <mca at tams.com.au>)

This is not actually correct.  It is quite possible and not that difficult
to have the same IP address on every interface for a machine.  The simplest
case of this is where you have each interface on a different physical subnet
(which is exactly the situation here).  To make this work, you assign the IP
address to eth0 as was done correctly in the original setup.  The trick is
to have the routing table configured correctly.  Basically, you add a
routing entry for each local physical subnet.  So in the case, you use

ifconfig eth0 203.3.126.129 
route add -net 203.3.126.128 netmask 255.255.255.248 eth0

Using the GUI admin tools with the distribution should allow the above
configuration to be set up automatically by setting the IP and netmask for
eth0

When you dial your ISP, if pppd is configure to add a default route (as it
should be), then it will automatically do

route add default ppp0 (or something similar)

You should end up with "route -n" giving something like this....

www.xxx.yyy.zzz 0.0.0.0         255.255.255.255 UH    0      0        0 ppp0
203.3.126.128   0.0.0.0         255.255.255.248 U     0      0        0 eth0
127.0.0.0       0.0.0.0         255.0.0.0       U     0      0        0 lo
0.0.0.0         www.xxx.yyy.zzz 0.0.0.0         UG    0      0        0 ppp0

The first line should be added automatically by pppd and tells the system
that there is a host www.xxx.yyy.zzz that can be reached via interface ppp0
(this will be the machine at the OTHER end of your ppp link, use "ifconfig
ppp0" if you want to verify the actual address).  The "H" part of "UH" means
it's a host route.

The second lines says there is a net route that says any machine from
203.3.126.128 to 203.3.126.135 can be reached via eth0.

The third line is the loopback route.  Any address that starts with 127 is
looped back using the local loopback device lo.

The fourth line is automatically added by pppd if the defaultroute option is
enabled (I think the default is enabled) and is the default route that says
any other addresses get routed via gateway www.xxx.yyy.zzz.

If your route table looks like this then the original configuration you were
trying should work unless ip masquerading is screwing you up by blocking any
routing.  I've never used Mandrake, perhaps someone who has could tell us if
routing is enabled in the kernel by default?

HTH

Cheers
Michael Anthon


<snip>
> 
> IPs are _always_ assigned to network interfaces, _not_ hosts. 
>  This is an
> important point!
> 
> If you've got a box with 5 ethernet cards, one on each of 5 networks,
> it's going to have _5_ IPs.  The box is seen as a host on 
> each of the 5
> networks.  You can then configure your computer to act as a 
> router between
> the 5 networks.  
<snip>

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