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1/30/2019
11:30 AM
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Access Control Lists: 6 Key Principles to Keep in Mind

Build them carefully and maintain them rigorously, and ACLs will remain a productive piece of your security infrastructure for generations of hardware to come.
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In an industry of constant, rapid change, an old-school security tool remains an effective piece of an overall security. Access Control Lists (ACLs) that specify precise rules for destinations and protocols allowed or forbidden, are the foundation of firewalls. And while firewalls have advanced to use analysis of packet contents and behavior, ACLs have not gone away.

There are a number of reasons why ACLs endure. The first, and most important, is that they work. ACLs are straight-forward, conceptually simple ways to limit traffic to and from known (or suspected) malicious addresses and to clear traffic to and from addresses known to be acceptable. Next, they play well with others. As Twitter user Frank Barton (@fbarton) wrote in response to a question about ACLs, "…much less cpu intensive than stateful and deep-packet. But…like Ogres, and onions…use layers. If you can block traffic at ACL, then pass remaining to “NGFW” [next-generation firewall] the fw [firewall] has less traffic to inspect."

As with all security measures, though, how an ACL is deployed will have a major impact on its effectiveness. Of course, precisely how the ACL is programmed will vary from manufacturer to manufacturer, and component to component, but there are key considerations that are true regardless of which device is hosting the ACL. Let's take a look at the principles to keep in mind to make ACLs an effective (and efficient) part of the overall security infrastructure.

(Image: photon_photo — stock.adobe.com)

 

Curtis Franklin Jr. is Senior Editor at Dark Reading. In this role he focuses on product and technology coverage for the publication. In addition he works on audio and video programming for Dark Reading and contributes to activities at Interop ITX, Black Hat, INsecurity, and ... View Full Bio

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paul.dittrich
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paul.dittrich,
User Rank: Strategist
1/30/2019 | 3:40:31 PM
Harnessing the power of ACLs
I could not agree more strongly with every point in your column.

It may be fashionable to claim there is no longer a network perimeter but I still strongly favor using the border router as a "garbage filter".

The BOGONs list? - Drop them all.  Invalid TCP flag combinations - Drop.  No Telnet in your environment?  No FTP?  No RDP?  - Block them all at the border router.

As mentioned in the post, the NGFW should take care of the deep packet inspection for only the traffic you potentially want inside your network.  That firewall should see very little traffic except for the known IPs, ports and protocols which are candidates to be allowed all the way in.

And an outbound ACL (a.k.a. egress filtering) is a very powerful weapon against data exfiltration and many types of malware.  You may still have a Trojan but if it can't phone home......
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