Isowall – A mini-firewall that completely isolates a target device from the local network

This is a mini-firewall that completely isolates a target device from the local network. This is for allowing infected machines Internet access, but without endangering the local network.

Building
This project depends upon libpcap, and of course a C compiler.
On Debian, the following should work:
# apt-get install git gcc make libpcap-dev
# git clone https://github.com/robertdavidgraham/isowall
# cd isowall
# make

This will put the binary isowall in the local isowall/bin directory.
This should also work on Windows, Mac OS X, xBSD, and pretty much any operating system that supports libpcap.
Running
First, setup a machine with three network interfaces.
The first network interface (like eth0) will be configured as normal, with a TCP/IP stack, so that you can SSH to it.
The other two network interfaces should have no TCP/IP stack, no IP address, no anything. This is the most important configuration step, and the most common thing you’ll get wrong. For example, the DHCP software on the box may be configured to automatically send out DHCP requests on these additional interfaces. You have to go fix that so nothing is bound to these interfaces.
To run, simply type:
# ./bin/isowall --internal eth1 --external eth2 -c xxxx.conf

where xxxx.conf contains your configuration, which is described below.

Configuration

The following shows a typical configuration file.

internal = eth1
internal.target.ip = 10.0.0.129
internal.target.mac = 02:60:8c:37:87:f3

external = eth2
external.router.ip = 10.0.0.1
external.router.mac = 66:55:44:33:22:11

allow = 0.0.0.0/0
block = 192.168.0.0/16
block = 10.0.0.0/8
block = 224.0.0.0-255.255.255.255
The target device we are isolating has the indicated IP and MAC address.
Only IPv4 and ARP packets are passed.
Outbound packets must have the following conditions:
  • source MAC address equal to internal.target.mac
  • destination MAC address equal to external.router.mac
  • EtherType of 0x800 or 0x806
  • source IPv4 address equal to internal.target.ip
  • destination IPv4 address within an allow range, but not in a block range
  • if an ARP packet, then the destination IPv4 address must equal that external.router.ip
  • if an ARP packet, must be a “request”
Inbound packets must have the following conditions:
  • destination MAC address equal to internal.target.mac
  • source MAC address equal to external.router.mac
  • EtherType of 0x800 or 0x806
  • destination IPv4 address equal to internal.target.ip
  • source IPv4 address within an allow range, but not in a block range
  • if an ARP packet, then the source IPv4 address must equal that external.router.ip
  • if an ARP packet, then must be a “reply”

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