Squid Reverse Proxy Server

I have a small problem for which a Squid reverse proxy server was the obvious problem, but I had the hardest time getting this to work as advertised. Why was it difficult? Undocumented options.

Here's the problem: I've got three webservers with identical content. I want eveybody from comcast.net to hit one, verizon.net to hit the second, and everybody else to hit the third. Squid can be configured to grab the requests, do the lookup on the domain, and forward them to the correct server. Here's a snippet of the configuration that worked:

http_port 80 accel defaultsite=gfs2.terran.lan
cache_dir null /null

acl first  src comcast.net
acl second src verizon.net
acl others src 0.0.0.0/0


cache_peer 192.168.69.59 parent 80 0 proxy-only \
  no-query no-digest originserver name=gfs3
cache_peer_access gfs3 allow first
http_access allow first

cache_peer 192.168.69.60 parent 80 0 proxy-only \
  no-query no-digest originserver name=gfs4
cache_peer_access gfs4 allow second
http_access allow second

cache_peer 192.168.69.61 parent 80 0 proxy-only \
  no-query no-digest originserver name=gfs2
cache_peer_access gfs3 allow others
http_access allow others