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Chapter 4
Transparent Proxy Caching
Dynamic bypass rules
When configured to do so, Traffic Server watches for certain protocol interoperability errors, and as it detects
errors, it configures the ARM to bypass the proxy for those clients and/or servers causing the errors.
In this way, the very small number of clients or servers that do not operate correctly through proxies are auto-
detected and routed around Traffic Server, so they can continue to function normally (but without the
improvement of caching).
You can configure Traffic Server to dynamically bypass the cache for any of the following triggering
conditions:
For example, when Traffic Server is configured to bypass on authentication failure (
403 Forbidden
), if any
request to a host returns a 403 error, the ARM generates a destination bypass rule for the host’s IP address. All
requests to that host are bypassed until the next Traffic Server restart.
In another example, if the ARM detects that a client is sending a non-HTTP request on port 80 to a particular
origin server, the ARM generates a source/destination rule. All requests from that particular client to the origin
server are bypassed; requests from other clients are not bypassed.
Bypass rules that are generated dynamically are purged after a Traffic Server restart. If you want to preserve
dynamically generated rules, you can save a snapshot of Traffic Server’s current set of bypass rules. See
Viewing the current set of bypass rules‚ on page 32
.
Setting dynamic bypass rules
By default, Traffic Server is not configured to bypass the cache when it encounters HTTP errors or non-HTTP
traffic on port 80. You must enable dynamic bypass rules in the
records.config
file.
To set dynamic bypass rules:
1. Telnet into the HP web cache appliance and select Shell Access as described in
Overview of Access
Methods‚ on page 7
.
2. Open the
records.config
file located in the Traffic Server’s
config
directory with Vi.
3. Edit the following variables in the
ARM (Transparency Configuration)
section of the file:
NOTE
Do not confuse bypass rules with client access control lists. Bypass rules are generated
in response to interoperability problems. Client access control is simply restriction of
the client IP addresses that can access the Traffic Server cache as described in
Controlling client access to the Traffic Server proxy cache‚ on page 81
.
Error code
Description
N/A
non-HTTP traffic on port 80
400
Bad Request
401
Unauthorized
403
Forbidden (authentication failed)
405
Method not allowed
406
Not Acceptable (access)
500
Internal server error