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.
Then there is no MAC address filtering being applied.
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?
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
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
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
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/