MAC Spoofing with Netgraph

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Contents

Prerequisites

  • Kernel in static or modular configuration that has the following enabled: ng_ether, ng_eiface, and ng_bridge.
  • A fair amount of knowledge.
  • A machine that you can break the crap out of.

Background

  • We will be taking a machine with a physical network interface, adding a virtual interface, bridging them, and using the virtual interface in a live environment.
  • There is an awful lot to netgraph(4). Read the manual pages often.

Assumptions

  • We have a machine with (1) NIC, labelled 'fxp0'; its IP is "192.168.2.5/24".
  • We can remove it from the network for testing. It will not piss off the boss or coworkers.

Configuration

  • First, if you're using the kernel modules, load them:
 # kldload ng_ether
 # kldload ng_eiface
 # kldload ng_bridge
  • Next, create the eiface.
  • 'ng_eiface' has exactly one hook, to a lower-level ng_ether node.
 # ngctl mkpeer . eiface hook ether
  • Now create and name the bridge.
  • 'ng_bridge' has NG_BRIDGE_MAX_LINKS hooks, named 'linkN'.
  • 'ng_bridge' hook 'link0' connects the downstream ('lower') from ngeth0:
 # ngctl mkpeer ngeth0: bridge lower link0
 # ngctl name ngeth0:lower bridge0
  • Now setup the ngeth0 interface:
 # ifconfig ngeth0 link 00:de:ad:be:ef:00
 # ifconfig ngeth0 inet 192.168.2.5 netmask 0xffffff00 down
  • Now connect the ethernet device to the bridge.
  • 'ng_eiface' hook 'upper' for fxp0: leads upstream to the bridge.
 # ngctl connect fxp0: bridge0: upper link1
  • Now the virtual interface to the other half of the bridge.
  • 'ng_eiface' hook 'upper' for ngeth0: leads upstream to the bridge.
 # ngctl connect ngeth0: bridge0: upper link2
  • Now setup the physical interface:
 # ngctl msg fxp0: setpromisc 1
 # ngctl msg fxp0: setautosrc 0
 # ifconfig fxp0 delete
  • And finally, connect it to the last piece of the bridge:
 # ngctl connect fxp0: bridge0: lower link3
  • Now on your upstream router (if you can access it):
 # arp -a | grep "192\.168\.2\.5"
 machine.domain.com (192.168.2.5) at 00:de:ad:be:ef:00 on em0
  • You may need to re-add your default route:
 # route add default .......
  • Thats it. For an explanation, we'll have to work on that.
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