How do I block Skype

[mell0n]

I'm concerned about users implementing Skype on our network, what measures can be taken to prevent this?

[Bobby Thekkekandam]

Hi,

On a router, you can use nbar to match on the Skype protocol and then you can either block or limit the stream coming into your network.

Below are 2 links. One that talks about nbar and how to deploy it and the second is a link to the Skype pdlm file to add to you router so that nbar can use this file to match the traffic.

Link on how to ebable nbar on your router.

http://www.cisco.com/en/US/products/sw/iosswrel/ps1835/products_configuration_guide_chapter09186a00800c75d0.html

Link to the pdlm download for the Skype pdlm file

http://www.cisco.com/cgi-bin/tablebuild.pl/pdlm

-Bobby

Hope that helps, please rate helpful posts.

[mell0n]

Thanks for the assistance, I'm unable to locate the file specified in the second link. Any thoughts?

[Bobby Thekkekandam]

Hi,

I double checked, and I had seen the readme for skype in the pdlm download page. Turns out that there's actually no separate pdlm file for Skype, it was added directly into the IOS. You need at least

12.4(4)T to get Skype support in NBAR. This is documented here :

http://www.cisco.com/en/US/products/ps6441/prod_bulletin09186a00804a8728.html#wp1064474

"Skype Classification via NBAR Packet Description Language Modules Skype is a popular VoIP telephony service that allows users to speak, send instant messages, and/or send files to one another via the Internet. This functionality provides the ability to recognize Skype application traffic in Cisco IOS Software. The NBAR PDLM for Skype classification is

integrated into Cisco IOS Software. There will not be a downloadable PDLM for Skype because of infrastructure changes required to accommodate Skype application classification."

HTH,

Bobby

[mell0n]

Thanks again for you assitance