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I want to isolate a host on my home intranet using iptables on my linux router. So say for instance, I have a host that has the IP of and I want it to be able to talk to the rest of the Internet, but I don't want the router to allow it to talk to any other host in However, I want to be able to allow hosts in to connect to on port 80 only as long as the connection isn't created on the host. I am doing this in case is compromised, so it can't talk to the rest of my network.

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it's related to your interfaces.please edit and explain more. –  PersianGulf Sep 19 '13 at 18:35
I am not sure what other information you are looking for. I have two interfaces on the router, a wan and lan. iptables is already setup as a NAT as well. –  sparticvs Sep 19 '13 at 18:43
I read again , you don't ban in layer 4, you should do it in layer 3, you shoud ban in switch. –  PersianGulf Sep 19 '13 at 18:49
Because before your iptables hosts able to watch together. –  PersianGulf Sep 19 '13 at 18:50

2 Answers 2

up vote 2 down vote accepted

You're most probably doing it wrong. Your router can't prevent from talking to the rest of the subnet, because they're in the same subnet. A packet from to another host in this subnet will not pass through the router, so you can't filter it.

What you need to do is to set up a separate subnet, let's say for example and put into that subnet, for example with the new IP Then connect this subnet to a separate interface of your router, and configure this interface to an IP like Then you can set up your routing rules as desired:

  • Allow established and related connections
  • Allow to connect to the Internet
  • Allow to connect to the Internet
  • Allow connections from to
  • Deny everything else
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So I did that originally, so I am glad that that was the right path to take. Originally, I had it so that the host was in and my regular subnet was I added to eth1 on my router, which also was However, I had a routing issue between the two networks, which didn't make sense to me. Thoughts? –  sparticvs Sep 19 '13 at 19:59
"Your router can't prevent from talking to the rest of the subnet, because they're in the same subnet" - if the computers on the network are directly connected to the router, it should be possible to drop undesired packets even on the usually bridged LAN, shouldn't it? –  peterph Sep 19 '13 at 20:04
@peterph I think you would have to connect each computer to a separate interface on the router and then you would have to set up a /31 or /30 mini subnet for each computer, which of course doesn't seem very practical. As soon as multiple computers are directly connected via hub/switch/bridge the packets between these computers would no longer pass through the router. –  Martin von Wittich Sep 19 '13 at 20:13
@sparticvs please try to restore this configuration then [or: wait for other answers in case I'm wrong] and then edit your posting to reflect it. Explain the issues you're having and then we can take it from there. –  Martin von Wittich Sep 19 '13 at 20:14
@peterph wow, you've got me there... I had never heard of ebtables before now :). Yes, that could work in the right circumstances, but unless you really need the ability to selectively pass or filter Ethernet frames, it's probably the wrong tool for the job. –  Martin von Wittich Sep 19 '13 at 20:49

To do it you should ban in layer 3 not layer 4, or if you do in layer 4, you should define a new subnet.

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