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I'm a new system administrator of an existing Linux network. Apparently there is MAC address filtering there. How could I allow a specific MAC to connect to the network?

The INPUT, FORWARD and OUTPUT chains of iptables are empty.

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    How did you come to the conclusion that MAC addresses are filtered? Have you checked your network equipment (e. .g managed switch)?
    – joschi
    Jun 28, 2010 at 8:42
  • @joshi: 1. I tried a couple of laptops on different patch-cords. They can't connect. 2. I was asked to "allow a specific mac-address on the net" from one of the users.
    – Alex
    Jun 28, 2010 at 8:46
  • Maybe you just need to add the machines to the DHCP server config.
    – James
    Jun 29, 2010 at 0:09
  • Do the machines negotiate a link when they're plugged in?
    – Jodie C
    Jul 15, 2011 at 13:52

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There is a program on Linux called ebtables that allows filtering, logging, forwarding and other stuff based on MAC addresses (Layer 2), as opposed to iptables working with IP addresses (Layer 3). ebtables works similarly to iptables, might be worth it to try ebtables -L or so.

Alternatively your Linux system might have multiple interfaces junctioned in a bridge, but I'm not sure what sort of MAC filtering you can do with brctl.

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Re "The INPUT, FORWARD and OUTPUT chains of iptables are empty"

As ultrasawblade stated, ebtables is one possibility when a system is using a bridged interface.

Another possibility, that doesn't require a bridged interface, is to use the PREROUTING chain in the RAW table.

I do MAC address filtering in the RAW table all the time :-)

To look at the RAW table, as root check

iptables -L -v -t raw

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If there is MAC filtering, and no iptables rules related to MAC filtering, then there is certainly ebtables filtering.

Related link is here: http://ebtables.sourceforge.net/

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Apparently there is MAC address filtering

....

The INPUT, FORWARD and OUTPUT chains of iptables are empty

Then there is no MAC address filtering being applied.

How could I allow a specific MAC to connect to the network?

What network? Do you mean the Linux box is acting as a router?

Or are they having problems connecting to services runing on the Linux box? What services? Are the daemons running? Can you connect to them from the localhost?

C.

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