Back To Basics: Troubleshooting Proxy Server 2.0 Page 6

Thomas Shinder

Client-side Array Routing

When a Proxy Server that is a member of a Proxy
Array receives a request for an Internet object, it must perform a series of
calculations to determine where the object is located in the Web Cache, and if
it is located in there at all. This takes a number of processor cycles on the
Proxy Array member. When Array members must to all the intra-array cache route
processing, it can have a negative effect on the overall performance of the
array.

To reduce the impact of array routing on the
Proxy Servers, you can have the clients perform this function. In order to do
so, you must configure the clients to use the Automatic Configuration Script,
which can be configured in the client’s browsers. This scripts takes the
format:

and you replace with the name
of a Proxy Server that is a member of an array.

When you configure the clients to use this
script, the clients will perform the routing functions necessary to identify the
location of web objects that may be located in cache. This offloads the
processing overhead on the Proxy Servers, and distributes it across all the
proxy clients on the network.

Keep in mind of who the Proxy Clients are on your
network. Client workstations are always thought of as Proxy Server client.
However, another important Proxy Server client are down-stream Proxy Servers in
a Proxy chain. Be sure to configure the down-stream servers to use the automatic
configuration script as well.

Proxy Server can also act as a rudimentary
firewall product by implementing Packet Filtering on the external
interface. The proxy server will examine all packets received on the external
interface and assess whether or not that packet should receive further
processing. If the packet arriving on the external interface does not meet the
requirements set for the packet filters, the packet will be immediately dropped
without any futher processing.

The key problem a lot of administrators
implementing Proxy Server run into is that they don’t realize that these
packet filters apply to the external interface only. The packet filter
settings you configure on the Proxy Server do not apply to any of the internal
interfaces. In addition, you won’t even be able to configure packet filters at
all unless you have configured an external interface on the Proxy Server.

In this next installment of the Back to Basics,
we’ll go over issues related to troubleshooting the Web Proxy, WinSock Proxy,
and SOCKS Proxy Service. We’ll also cover special configuration issues and DMZ
subnets.