MAC Verification



Beginning with Shorewall version 1.3.10, 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.

You must have the iproute package (ip utility) installed to use MAC Verification and your kernel must include MAC match support (CONFIG_IP_NF_MATCH_MAC - module name ipt_mac.o).

There are four components to this facility.
  1. The maclist interface option in /etc/shorewall/interfaces. When this option is specified, all traffic arriving on the interface is subjet to MAC verification.
  2. 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.
  3. The /etc/shorewall/maclist file. This file is used to associate MAC addresses with interfaces and to optionally associate IP addresses with MAC addresses.
  4. 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:

Example 1: Here are my files:

/etc/shorewall/shorewall.conf:
     MACLIST_DISPOSITION=REJECT
MACLIST_LOG_LEVEL=info
/etc/shorewall/interfaces:
     #ZONE           INTERFACE       BROADCAST       OPTIONS
net eth0 206.124.146.255 norfc1918,filterping,dhcp,blacklist
loc eth2 192.168.1.255 dhcp,filterping,maclist
dmz eth1 192.168.2.255 filterping
net eth3 206.124.146.255 filterping,blacklist
- texas 192.168.9.255 filterping
loc ppp+ - filterping
/etc/shorewall/maclist:
     #INTERFACE              MAC                     IP ADDRESSES (Optional)
eth2 00:A0:CC:63:66:89 192.168.1.3 #Wookie
eth2 00:10:B5:EC:FD:0B 192.168.1.4 #Tarry
eth2 00:A0:CC:DB:31:C4 192.168.1.5 #Ursa
eth2 00:06:25:aa:a8:0f 192.168.1.7 #Eastept1 (Wireless)
eth2 00:04:5A:0E:85:B9 192.168.1.250 #Wap
As shown above, I use MAC Verification on my local zone.

Example 2: Router in Local Zone

Suppose now that I add a second ethernet segment to my local zone and gateway that segment via a router with MAC address 00:06:43:45:C6:15 and IP address 192.168.1.253. Hosts in the second segment have IP addresses in the subnet 192.168.2.0/24. I would add the following entry to my /etc/shorewall/maclist file:
     eth2                     00:06:43:45:C6:15       192.168.1.253,192.168.2.0/24
This entry accomodates traffic from the router itself (192.168.1.253) and from the second LAN segment (192.168.2.0/24). Remember that all traffic being sent to my firewall from the 192.168.2.0/24 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.

Updated 12/29/2002 - Tom Eastep

Copyright © 2001, 2002 Thomas M. Eastep.