You may find yourself in a situation where more than one hostname resolves to Squid’s IP address. For example, both sv.us.ircache.net and sv.cache.nlanr.net resolve to 188.8.131.52. If you have neighbors, they may send requests for certain Squid-specific internal URLs, as in the case of Cache Digests. These URLs might contain either hostname. You must use this directive to tell Squid that it is known by names other than its visible_hostname.
hostname_aliases this.host.name that.host.name