ip conflict with proxy arp

ip conflict with proxy arp

[Rohan Almeida]

HI,
I've got a proxy arp setup with iptables and tc.
 
on eth0 i have a route to 172.16.2.0/24 network
on eth1 is the LAN of 172.16.1.0/24 network
 
I have enabled proxy arp on both interfaces.
Now accordingly, the interface will respond
to all ARP requests for which it has a route to.
 
Noy my setup is such, that a user on the LAN,
would like to have an ip from the 172.16.2.0/24 network.
 
But unfortunately, when he tries to allocate an
ip like 172.16.2.1 he gets an ip conflict.
 
I also know why he is getting it!
But is there any way out of this??
 
Something like, tell the linux server to respond for
ARP requests for the 172.16.2.0/24 network but at the
same time if a machine is trying to use an ip for itself,
then it should not respond.
 
Help!
 
--
arc_of_descent

Re: ip conflict with proxy arp

[Antony Stone]

On Tuesday 29 October 2002 6:58 am, Rohan Almeida wrote:

> HI,
> I've got a proxy arp setup with iptables and tc.
>
> on eth0 i have a route to 172.16.2.0/24 network
> on eth1 is the LAN of 172.16.1.0/24 network
>
> I have enabled proxy arp on both interfaces.
> Now accordingly, the interface will respond
> to all ARP requests for which it has a route to.
>
> Noy my setup is such, that a user on the LAN,
> would like to have an ip from the 172.16.2.0/24 network.

What, whilst still plugged in to eth1 ?   Why ?

> But unfortunately, when he tries to allocate an
> ip like 172.16.2.1 he gets an ip conflict.
>
> I also know why he is getting it!
> But is there any way out of this??
>
> Something like, tell the linux server to respond for
> ARP requests for the 172.16.2.0/24 network but at the
> same time if a machine is trying to use an ip for itself,
> then it should not respond.

How are you allocating your addresses on the two networks at the moment ?

If it's a system administrator handing out static addresses and recording 
who's got what, then tell the person on the LAN to go to the sysadmin and ask 
for an unused address.

If it's a DHCP server handing out addresses on request, try setting up a 
DHCRELAY (there's another thread going in this mailing list at the moment 
about getting that working with netfilter) so pass addresses from one network 
to the other.

However, I still want to ask: why does someone on eth1 want an IP address 
which belongs on eth0 ?

Antony.

-- 

There are only 10 types of people in the world:
those who understand binary notation,
and those who don't.

Re: ip conflict with proxy arp

[Rohan Almeida]

Antony Stone <Antony@Soft-Solutions.co.uk> thus wrote:
> On Tuesday 29 October 2002 6:58 am, Rohan Almeida wrote:
> > Noy my setup is such, that a user on the LAN,
> > would like to have an ip from the 172.16.2.0/24 network.
> 
> What, whilst still plugged in to eth1 ?   Why ?

Honestly, i have no clue,
Its just a network setup which I have
to solve somewhere.
I tried explaining them the problem but
they are adamant on using the existing setup.
 
> How are you allocating your addresses on the two networks at the moment ?
> 
> If it's a system administrator handing out static addresses and recording 
> who's got what, then tell the person on the LAN to go to the sysadmin and ask 
> for an unused address.
> 
> If it's a DHCP server handing out addresses on request, try setting up a 
> DHCRELAY (there's another thread going in this mailing list at the moment 
> about getting that working with netfilter) so pass addresses from one network 
> to the other.

Its a DHCP server
I'll take a look at DHCPRELAY.
Maybe it can help me
Thanx

--
arc_of_descent