LARTC - Dec 2002 - Re: routing problem with new subnet..

guys, i need some help with some problems I''m having

I have a debian (woody) box acting as router for my network and I am trying
to setup a dmz (210.xxx.xxx.225/29).

anyway, whenever a request comes in for one of the boxes in the dmz the
gateway box doesn''t seem to answer any arp requests for it. So the
connection goes nowhere. How do i fix it? I''ve tried playing with arp
proxy
and manual arp entries to no avail. Do I need to add an extra route?

system details:
debian woody w/ 2.4.18 kernel
iproute       20010824-8
iptables     1.2.6a-5

route table:
210.xxx.xxx.140/30 dev eth0  proto kernel  scope link  src 210.xxx.xxx.142
<-- eth0
210.xxx.xxx.224/29 dev eth2  proto kernel  scope link  src 210.xxx.xxx.225
<-- eth2
192.168.0.0/24 dev eth1  proto kernel  scope link  src 192.168.0.1   <--
eth1
default via 210.xxx.xxx.141 dev eth0

Any more info needed?

Regards,

Craig Reeson  RHCE
Senior Engineer
Bluechip Infotech (formerly Servex Australia)
Ph. (02) 8745 8465
Mob. 0413 018602


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: I have a debian (woody) box acting as router for my network and I am trying
 : to setup a dmz (210.xxx.xxx.225/29).

 <routing table snipped>

This is a classic case of a breaking a network in two with proxy ARP.  You 
can do this exactly as you indicate (assuming the xxx.xxx numbers are all 
accurate).

 : anyway, whenever a request comes in for one of the boxes in the dmz the
 : gateway box doesn''t seem to answer any arp requests for it. So the
 : connection goes nowhere. How do i fix it? I''ve tried playing with
arp proxy
 : and manual arp entries to no avail. Do I need to add an extra route?

The routes look fine, according to the snipped routing table.

There are (at least) two ways to do it.  I haven''t documented the
second
way yet...keep looking around but you can read up on one way to do it here 
(with script and config file):

  http://plorf.net/linux-ip/html/adv-proxy-arp.htm

One thing people frequently forget when using proxy ARP techniques is:

  the upstream router (here at 210.xxx.xxx.141) needs to have
  a /30 prefix length and a static route

               OR

  the upstream router needs to have a a /29 prefix length, and the
  proxy ARPing device needs to proxy ARP for the "internal" network

I''d recommend using tcpdump on both eth0 and eth2 to determine where
the
problem is.

-Martin


-- 
Martin A. Brown --- SecurePipe, Inc. --- mabrown@securepipe.com


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