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We have simple setup of firewall/gateway at out office using iptables. The public IP address is on eth2 and eth1 is local ip address (local static) and it runs dhcp server on it. Normally we keep some data on it.

From past few days as we observed the content the copied from firewall/gateway to any local machine the data will be copied from the External IP to local machine.When a large data flow occurs the wireless goes down sometime.

The tcpdump shows the packets are coming from external interface. My question is when the firewall/gateway has local ip and the data getting copied / syncing from external interface to any local machine. WHY?

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I didn't really get your question, maybe you can start by dumping your iptables rules here :-) – gutherzig Apr 13 '11 at 4:02

You don't provide much to go on here. We need a more complete network diagram or at least the specifics of the network to figure out your problem. Feel free to obfuscate the real public IP if you like.

  1. Are you running NAT on your firewall/gateway?
  2. What is your network for your local machines? (
  3. What traffic are you talking about specifically that is causing the problems port/protocol/source/destination.
  4. On which interface are you running tcpdump and have you tried -i any?
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