On the test I use the Cisco Catalyst 6509-E switch.
Suppose we need to block access to users to a certain site, a network node, or for example a social network VKontakte.
First, we know the range of IP addresses on which the site is located, for example, we search VKontakte on bgp.he.net, here is for example the list of subnets for one of the AS belonging to VKontakte http://bgp.he.net/AS47541#_prefixes
And create an extended ACL for example with the name BLOCKSOCIAL:
ip access-list extended BLOCKSOCIAL deny ip any 188.8.131.52 0.0.63.255 deny ip any 184.108.40.206 0.0.7.255 deny ip any 220.127.116.11 0.0.7.255 deny ip any 18.104.22.168 0.0.15.255 deny ip any 22.214.171.124 0.0.63.255 deny ip any 126.96.36.199 0.0.0.255 deny ip any 188.8.131.52 0.0.3.255 permit ip any any exit
The rule above indicates that you want to block traffic to the specified networks coming from all (any) sources.
You can specify as a source a specific network or for example one address to deny access to another address:
deny ip host 192.168.5.1 host 192.168.11.54
The line “permit ip any any” should be necessary at the end.
Instead of a subnet mask, you need to specify the Wildcard, for example, for the mask /24, specify 0.0.0.255, for /22 – 0.0.3.255, etc., you can look at and count on any IP calculator.
If you want to block more sites, we’ll add the addresses to the same ACL, since only one can be applied to the ACL interface.
Apply the created ACL to the port looking towards the clients:
interface GigabitEthernet1/1 ip access-group BLOCKSOCIAL in
Or, to write less only to the server’s server port on the Internet, if there is one:
interface TenGigabitEthernet3/2 ip access-group BLOCKSOCIAL in
You can cancel the ACL interface as follows:
no ip access-group BLOCKSOCIAL in
Delete the ACL like this:
no ip access-list extended BLOCKSOCIAL