Cisco 500 Series, Configuration Manual

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20-6
Cisco Security Appliance Command Line Configuration Guide
OL-12172-03
Chapter 20 Applying Filtering Services
Filtering URLs and FTP Requests with an External Server
Buffering the Content Server Response
When a user issues a request to connect to a content server, the security appliance sends the request to
the content server and to the filtering server at the same time. If the filtering server does not respond
before the content server, the server response is dropped. This delays the web server response from the
point of view of the web client because the client must reissue the request.
By enabling the HTTP response buffer, replies from web content servers are buffered and the responses
are forwarded to the requesting client if the filtering server allows the connection. This prevents the
delay that might otherwise occur.
To configure buffering for responses to HTTP or FTP requests, perform the following steps:
Step 1 To enable buffering of responses for HTTP or FTP requests that are pending a response from the
filtering server, enter the following command:
hostname(config)# url-block block block-buffer-limit
Replace block-buffer with the maximum number of HTTP responses that can be buffered while awaiting
responses from the url-server.
Note
Buffering URLs longer than 3072 bytes are not supported.
Step 2
To configure the maximum memory available for buffering pending URLs (and for buffering long
URLs), enter the following command:
hostname(config)#
url-block mempool-size
memory-pool-size
Replace memory-pool-size with a value from 2 to 10240 for a maximum memory allocation of 2 KB to
10 MB.
Caching Server Addresses
After a user accesses a site, the filtering server can allow the security appliance to cache the server
address for a certain amount of time, as long as every site hosted at the address is in a category that is
permitted at all times. Then, when the user accesses the server again, or if another user accesses the
server, the security appliance does not need to consult the filtering server again.
Note
Requests for cached IP addresses are not passed to the filtering server and are not logged. As a result,
this activity does not appear in any reports. You can accumulate Websense run logs before using the
url-cache command.
Use the url-cache command if needed to improve throughput, as follows:
hostname(config)# url-cache dst | src_dst size
Replace size with a value for the cache size within the range 1 to 128 (KB).
Use the dst keyword to cache entries based on the URL destination address. Select this mode if all users
share the same URL filtering policy on the Websense server.