I will use the routers so we can generate some traffic between the different security levels. Let’s take a look at a Cisco ASA firewall with three interfaces so you can see this behavior in action, here’s the topology I will use:Ībove you see the Cisco ASA in the middle with three interfaces: You can create as many security levels as you want… Traffic from the DMZ however can’t go to the inside (without an access-list) because traffic from security level 50 is not allowed to reach security level 100. This means that traffic is allowed from our inside network to the DMZ (security level 100 -> 50) and also from the DMZ to the outside (security level 50 -> 0). Security level 1 – 99: We can create any other security levels that we want, for example we can use security level 50 for our DMZ.Since this is the highest security level, by default it can reach all the other interfaces. Security level 100: This is the highest security level on our ASA and by default this is assigned to the “inside” interface.Since there is no lower security level this means that traffic from the outside is unable to reach any of our interfaces unless we permit it within an access-list. Security level 0: This is the lowest security level there is on the ASA and by default it is assigned to the “outside” interface.Here are a couple of examples of security levels: Each interface on the ASA is a security zone so by using these security levels we have different trust levels for our security zones.Īn interface with a high security level can access an interface with a low security level but the other way around is not possible unless we configure an access-list that permits this traffic. The higher the security level, the more trusted the interface is.
The Cisco ASA Firewall uses so called “security levels” that indicate how trusted an interface is compared to another interface.
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