Cisco PIX 525 Spécifications télécharger pdf (Page 146)

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Cisco PIX Firewall and VPN Configuration Guide

78-15033-01

Chapter 3 Controlling Network Access and Use

Filtering Outbound Connections

Buffering HTTP Replies for Filtered URLs

By default, when a user issues a request to connect to a specific website, the PIX Firewall sends the

request to the web server and to the filtering server at the same time. If the filtering server does not

respond before the web content server, the response from the web server is dropped. This delays the web

server response from the point of view of the web client.

By enabling the HTTP response buffer, replies from web content servers are buffered and the responses

will be forwarded to the requesting user if the filtering server allows the connection. This prevents the

delay that may otherwise occur.

To enable the HTTP response buffer, enter the following command:

url-block block block-buffer-limit

Replace block-buffer-limit with the maximum number of blocks that will be buffered. The permitted

values are from 0 to 128, which specifies the number of 1550-byte blocks that can be buffered at one

time.

Filtering Long URLs with the Websense Filtering Server

Note PIX Firewall Versions 6.2 and higher support a fixed, maximum URL length of 1159 bytes for the N2H2

filtering server.

To increase the maximum length of a single URL that can be sent to a Websense filtering server, enter

the following command:

url-block url-size long-url-size

Replace long-url-size with a value from 2 to 4 for a maximum URL size of 2 KB to 4 KB.

To configure the maximum memory available for buffering long URLs, enter the following command:

url-block url-mempool 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.

Filtering HTTPS and FTP Sites

PIX Firewall Version 6.3 introduces support for filtering of HTTPS and FTP sites for Websense filtering

servers.

Note HTTPS and FTP filtering are not supported for the N2H2 filtering server.

HTTPS filtering works by preventing the completion of SSL connection negotiation if the site is not

allowed. The browser displays an error message such as “The Page or the content cannot be displayed.”

Because HTTPS content is encrypted, PIX Firewall sends the URL lookup without directory and

filename information.

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Cisco PIX 525 Spécifications Page 146