Copyright © 2001-2004 Thomas M. Eastep
Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover, and with no Back-Cover Texts. A copy of the license is included in the section entitled “GNU Free Documentation License”.
2004-01-06
Table of Contents
All traffic from an interface or from a subnet on an interface can be verified to originate from a defined set of MAC addresses. Furthermore, each MAC address may be optionally associated with one or more IP addresses.
MAC addresses are only visible within a ethernet segment so all MAC addresses used in verification must belong to devices physically connected to one of the LANs to which your firewall is connected.
Your kernel must include MAC match support (CONFIG_IP_NF_MATCH_MAC - module name ipt_mac.o).
There are four components to this facility.
The maclist interface option in /etc/shorewall/interfaces. When this option is specified, all traffic arriving on the interface is subjet to MAC verification.
The maclist option in /etc/shorewall/hosts. When this option is specified for a subnet, all traffic from that subnet is subject to MAC verification.
The /etc/shorewall/maclist file. This file is used to associate MAC addresses with interfaces and to optionally associate IP addresses with MAC addresses.
The MACLIST_DISPOSITION and MACLIST_LOG_LEVEL variables in /etc/shorewall/shorewall.conf. The MACLIST_DISPOSITION variable has the value DROP, REJECT or ACCEPT and determines the disposition of connection requests that fail MAC verification. The MACLIST_LOG_LEVEL variable gives the syslogd level at which connection requests that fail verification are to be logged. If set the the empty value (e.g., MACLIST_LOG_LEVEL="") then failing connection requests are not logged.
The columns in /etc/shorewall/maclist are:
The name of an ethernet interface on the Shorewall system.
The MAC address of a device on the ethernet segment connected by INTERFACE. It is not necessary to use the Shorewall MAC format in this column although you may use that format if you so choose.
An optional comma-separated list of IP addresses for the device whose MAC is listed in the MAC column.
Example 1. Here are my files (look here for details about my setup)
/etc/shorewall/shorewall.conf:
MACLIST_DISPOSITION=REJECT MACLIST_LOG_LEVEL=info |
/etc/shorewall/interfaces:
#ZONE INTERFACE BROADCAST OPTIONS net eth0 206.124.146.255 dhcp,norfc1918,routefilter,blacklist,tcpflags loc eth2 192.168.1.255 dhcp dmz eth1 192.168.2.255 WiFi eth3 192.168.3.255 dhcp,maclist - texas 192.168.9.255 |
/etc/shorewall/maclist:
#INTERFACE MAC IP ADDRESSES (Optional) eth3 00:A0:CC:A2:0C:A0 192.168.3.7 #Work Laptop eth3 00:04:5a:fe:85:b9 192.168.3.250 #WAP11 eth3 00:06:25:56:33:3c 192.168.3.225,192.168.3.8 #WET11 eth3 00:0b:cd:C4:cc:97 192.168.3.8 #TIPPER |
As shown above, I use MAC Verification on my wireless zone.
While marketed as a wireless bridge, the WET11 behaves like a wireless router with DHCP relay. When forwarding DHCP traffic, it uses the MAC address of the host (TIPPER) but for other forwarded traffic it uses it's own MAC address. Consequently, I list the IP addresses of both devices in /etc/shorewall/maclist.
Example 2. Router in Wireless Zone
Suppose now that I add a second wireless segment to my wireless zone and gateway that segment via a router with MAC address 00:06:43:45:C6:15 and IP address 192.168.3.253. Hosts in the second segment have IP addresses in the subnet 192.168.4.0/24. I would add the following entry to my /etc/shorewall/maclist file:
eth3 00:06:43:45:C6:15 192.168.3.253,192.168.4.0/24 |
This entry accomodates traffic from the router itself (192.168.3.253) and from the second wireless segment (192.168.4.0/24). Remember that all traffic being sent to my firewall from the 192.168.4.0/24 segment will be forwarded by the router so that traffic's MAC address will be that of the router (00:06:43:45:C6:15) and not that of the host sending the traffic.