Cisco 500 Series, Руководство по настройке

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20-8
Cisco Security Appliance Command Line Configuration Guide
OL-12172-03
Chapter 20 Applying Filtering Services
Filtering URLs and FTP Requests with an External Server
hostname(config)# filter url [ longurl-truncate | longurl-deny | cgi-truncate ]
The longurl-truncate option causes the security appliance to send only the hostname or IP address
portion of the URL for evaluation to the filtering server when the URL is longer than the maximum
length permitted. Use the
longurl-deny option to deny outbound URL traffic if the URL is longer than
the maximum permitted.
Use the cgi-truncate option to truncate CGI URLs to include only the CGI script location and the script
name without any parameters. Many long HTTP requests are CGI requests. If the parameters list is very
long, waiting and sending the complete CGI request including the parameter list can use up memory
resources and affect firewall performance.
Exempting Traffic from Filtering
To exempt specific traffic from filtering, enter the following command:
hostname(config)# filter url except source_ip source_mask dest_ip dest_mask
For example, the following commands cause all HTTP requests to be forwarded to the filtering server
except for those from 10.0.2.54.
hostname(config)# filter url http 0 0 0 0
hostname(config)# filter url except 10.0.2.54 255.255.255.255 0 0
Filtering HTTPS URLs
You must identify and enable the URL filtering server before enabling HTTPS filtering.
Note Websense and Smartfilter currently support HTTPS; older versions of Secure Computing SmartFilter
(formerly N2H2) did not support HTTPS filtering.
Because HTTPS content is encrypted, the security appliance sends the URL lookup without directory
and filename information. When the filtering server approves an HTTPS connection request, the security
appliance allows the completion of SSL connection negotiation and allows the reply from the web server
to reach the originating client. If the filtering server denies the request, the security appliance prevents
the completion of SSL connection negotiation. The browser displays an error message such as “The Page
or the content cannot be displayed.”
Note The security appliance does not provide an authentication prompt for HTTPS, so a user must
authenticate with the security appliance using HTTP or FTP before accessing HTTPS servers.
To enable HTTPS filtering, enter the following command:
hostname(config)# filter https port [ -port ] localIP local_mask foreign_IP foreign_mask
[ allow ]
Replace port [ -port ] with a range of port numbers if a different port than the default port for HTTPS (443)
is used.
Replace local_ip and local_mask with the IP address and subnet mask of a user or subnetwork making
requests.