Transparent Proxy Caching; Serving Requests Transparently; Arm Redirection - HP P4535A - Web Cache Server Appliance Administrator's Manual

4 Transparent Proxy Caching

The transparency option enables Traffic Server to respond to Internet requests without requiring users to
reconfigure their browser settings.
This chapter discusses the following topics.
Serving requests transparently‚ on page 22
ARM redirection‚ on page 22
Interception strategies‚ on page 23
Interception bypass‚ on page 28

Serving requests transparently

In non-transparent operations, client browsers must be configured to send web requests to the Traffic Server
proxy cache. Many sites have no direct control over user browser settings, making it necessary for site
administrators to tell users to configure their browsers to direct requests to a Traffic Server.
The transparency option enables Traffic Server to respond to Internet requests without requiring users to
reconfigure their browser settings. It does this by redirecting the traffic flow into the Traffic Server cache after
it has been intercepted by a Layer 4 switch or router.
Here's how Traffic Server transparent interception works:
1. Traffic Server intercepts client requests to origin servers. There are several ways to deploy Traffic Server
so that interception can take place. See
2. HP's Adaptive Redirection Module (ARM) redirects requests destined for origin servers to the Traffic
Server application. See
3. A very small number of clients and servers do not work correctly through proxies. Traffic Server identifies
these problem clients and servers dynamically, and the ARM adaptively disables interception for these
clients and servers, passing their traffic unimpeded to the origin server. Additionally, clients and servers
can be manually exempted from caching by configuring ARM. See
more information.
4. Traffic Server receives and begins processing the intercepted client requests as explained in
Understanding web proxy caching‚ on page
requested document or news article. If a request is a miss, Traffic Server retrieves the document from the
origin server and serves it to the client.
5. On the way back to the client, the ARM changes the source IP address to the origin server IP address and
the source port to the origin server port.

ARM redirection

The intercepted client requests that reach Traffic Server are addressed to an origin server. Traffic Server's
ARM readdresses requests to Traffic Server so that they can be served.
The ARM can make two changes to an incoming packet's address: its destination IP address and its destination
port. Typically, HTTP packet destination IPs and ports are readdressed with the IP address of Traffic Server,
and Traffic Server's HTTP proxy port (usually port 8080). NNTP packet destination IPs are readdressed with
the IP address of Traffic Server. If Traffic Server uses a port other than 119 for NNTP, the destination NNTP
port is readdressed as well. You configure packet readdressing in the /home/TS4/<version>/config/
file. This file contains redirection rules that specify how incoming packets should be
ipnat.conf
readdressed.
Interception strategies‚ on page 23
ARM redirection‚ on page 22
11. If a request is a cache hit, Traffic Server serves the
for details.
for details.
Interception bypass‚ on page 28 for
22