Let's say we want to block access to the creatively named www.badsite.com.
I bet you've already configured DNS server to resolve the name in your router, if not
Router(config)# ip name-server 18.104.22.168 22.214.171.124
Router# ping www.techrepublic.com
Translating "www.techrepublic.com"...domain server (126.96.36.199) [OK]
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 188.8.131.52, timeout is 2 seconds:
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/1/4 ms
To actually block the undesirable Web site, we need to create an access control list (ACL) to define exactly what we want to block. Here's an example:
Router(config)# access-list 101 deny tcp any host www.badsite.com eq www
Allow to all rather than above
Router(config)# access-list 101 permit tcp any any eq www
Check your access like in router
Router# sh run | inc access-list 101
access-list 101 deny tcp any host 184.108.40.206 eq www log <-- you can block by address and also using log to monitor with syslog. i.e Kiwi Syslog Server.