Label Servers
Because proxy servers must deal with the entire data stream, they must be
scaled to handle all of the data. Label servers only deal with the actual
data being filtered - usually the URL and a bit of additional information
from the HTTP request headers. This allows them to concentrate solely on
filtering, offering much higher performance. In lab tests I've seen an
improvement of 200 times (from 25 requests per second to 5000 requests
per second) on identical hardware using identical filtering software
and identical lists.
Label servers must be used in conjunction with some other software, as they
don't offer a complete solution by themselves. This can either be proxy
software, client software, or software embedded into a routing or switching
device.
For example, Internet Explorer includes a PICS client which can be used
with label servers. Unfortunately, there are no large-scale
implementations of compatible label servers, so the capability is seldom,
if ever, used.
There is at least one commercial implementation of a label server which
can communicate with the freely available Squid proxy server. There are
not yet any announced label server products that work with routers or
switches.
Next: Packet Interception