You should use a a supported 3rd party app like Steven suggested. You could also configure URL filtering, explicity deny the domains you want blocked then change the allowmode to permit. This could cause high CPU utilization, so proceed with care. You can reference pg 435-436 in Richard Deals 'Cisco Router Firewall Security' for more info.

Following is the example to perform URL filtering using CBAC without using

web filtering servers.

# ip urlfilter exclusive-domain deny .yahoo.com

# ip urlfilter exclusive-domain deny .hotmail.com

# ip inspect name fire http urlfilter

Reference :-

http://www.cisco.com/en/US/docs/ios/12_2t/12_2t15/feature/guide/ftwebsen.htm

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