As you are using RHE 9 it might not help you but still try below link if it works.
Courtesy :
http://wiki.squid-cache.org/SquidFaq/SquidAcl
MAC address is only available for clients that are on the same subnet. If the client is on a different subnet, then Squid can not find out its MAC address as the MAC is replaced by the router MAC when a packet is router.
To use ARP (MAC) access controls, you first need to compile in the optional code. Do this with the --enable-arp-acl configure option:
% ./configure --enable-arp-acl ...
% make clean
% make
If src/acl.c doesn't compile, then ARP ACLs are probably not supported on your system.
If everything compiles, then you can add some ARP ACL lines to your squid.conf:
acl M1 arp 01:02:03:04:05:06
acl M2 arp 11:12:13:14:15:16
http_access allow M1
http_access allow M2
http_access deny all