Cisco IOS Time Based Access-List


(Rene Molenaar) #1

This topic is to discuss the following lesson:


(ruby p) #2

is this how most companies block access, i think we use something called websense?

 

also with facbeook having so many webservers in a farm for redundancy would you in real world scendario block by ip, or hostname?

 

 


(Rene Molenaar) #3

Hi Ruby,

The time based access-list is basically the “poor man’s” solution to block access on routers. You can use access-lists only to filter on L3/L4 information (IP addresses, protocols and port numbers) so you can’t filter based on hostnames.

One way to get around this is to block all prefixes that belong to a certain AS. For example, facebook uses AS 32934. We can find their prefixes with whois:

$ whois -h whois.radb.net -- '-i origin AS32934' | grep 'route:'
route: 204.15.20.0/22
route: 69.63.176.0/20
route: 66.220.144.0/20
route: 66.220.144.0/21
route: 69.63.184.0/21
route: 69.63.176.0/21
route: 74.119.76.0/22
route: 69.171.255.0/24
route: 173.252.64.0/18
route: 69.171.224.0/19
route: 69.171.224.0/20
route: 103.4.96.0/22
route: 69.63.176.0/24
route: 173.252.64.0/19
route: 173.252.70.0/24
route: 31.13.64.0/18
route: 31.13.24.0/21
route: 66.220.152.0/21
route: 66.220.159.0/24
route: 69.171.239.0/24
route: 69.171.240.0/20
route: 31.13.64.0/19
route: 31.13.64.0/24
route: 31.13.65.0/24
route: 31.13.67.0/24
route: 31.13.68.0/24
route: 31.13.69.0/24
route: 31.13.70.0/24
route: 31.13.71.0/24
route: 31.13.72.0/24
route: 31.13.73.0/24
route: 31.13.74.0/24
route: 31.13.75.0/24
route: 31.13.76.0/24
route: 31.13.77.0/24
route: 31.13.96.0/19
route: 31.13.66.0/24
route: 173.252.96.0/19
route: 69.63.178.0/24
route: 31.13.78.0/24
route: 31.13.79.0/24
route: 31.13.80.0/24
route: 31.13.82.0/24
route: 31.13.83.0/24
route: 31.13.84.0/24
route: 31.13.85.0/24
route: 31.13.86.0/24
route: 31.13.87.0/24
route: 31.13.88.0/24
route: 31.13.89.0/24
route: 31.13.90.0/24
route: 31.13.91.0/24
route: 31.13.92.0/24
route: 31.13.93.0/24
route: 31.13.94.0/24
route: 31.13.95.0/24
route: 69.171.253.0/24
route: 69.63.186.0/24
route: 31.13.81.0/24
route: 179.60.192.0/22
route: 179.60.192.0/24
route: 179.60.193.0/24
route: 179.60.194.0/24
route: 179.60.195.0/24
route: 185.60.216.0/22
route: 45.64.40.0/22
route: 185.60.216.0/24
route: 185.60.217.0/24
route: 185.60.218.0/24
route: 185.60.219.0/24
route: 129.134.0.0/16
route: 157.240.0.0/16
route: 204.15.20.0/22
route: 69.63.176.0/20
route: 69.63.176.0/21
route: 69.63.184.0/21
route: 66.220.144.0/20
route: 69.63.176.0/20

You could create a script that fetches these prefixes and updates your access-list every now and then.

For some more “serious” security, we use firewalls. Some firewalls are able to inspect the application layer so we can drop traffic based on the URL, payload, etc.

Rene


(Mohammad Hasanuz Zaman) #4

Dear Rene,

Thanks for your article…

What will be the command periodic if we want to block traffic from Sunday to Thrusday ?

br//
zaman


(Rene Molenaar) #5

Hi Zaman,

You can use some of the default periodic options:

Router(config-time-range)#periodic ?
  Friday     Friday
  Monday     Monday
  Saturday   Saturday
  Sunday     Sunday
  Thursday   Thursday
  Tuesday    Tuesday
  Wednesday  Wednesday
  daily      Every day of the week
  weekdays   Monday thru Friday
  weekend    Saturday and Sunday

Including “weekend”.

Rene