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ACLs, security levels and ASA



Let's say you have three interfaces with the following security levels: inside (100), outside (0) and dmz (30).

If you set an ACL on the DMZ interface with permit ip any any, will the DMZ be able to access the outside but not the inside? In other words, does the security settings of the interfaces come into play after the ACL? (assuming you have the correct NATs, etc...)

Next question. If you don't set an ACL on the DMZ interface, will DMZ hosts be able to access the

outside, but not the inside due to the security levels?

The reason I ask is when I run the conduit to ACL conversion utility (occ.exe) with the -pde option (which is supposed to simulate the default behaviour of the PIX), it puts ACLs on every interface. For the DMZ interface it puts an ACL with permit ip any any. Now, when I run the occ.exe without the -pde option, it doesn't put in the ACLs with the permit ip any any.

My basic question is why would it matter if you put acls with permit ip any any on dmz interfaces or not? Won't the traffic still follow the security level rules?



Frequent Contributor
Frequent Contributor

By default, higher security ints can talk to lower security ints, so dmz can talk to the internet, provided it has correct nat and global or static statements.

A permit ip any any acl on the dmz would only allow unfettered access to the inside hosts if there was an environment with no nat between the two interfaces.

What's curious though is if you run the occ.exe utility with the -pde option (which is supposed to simulate PIX default behavoiur) the output adds access-lists on DMZ interfaces with permit ip any any. How does that simulate the PIX default behavour if it would allow DMZ hosts unfettered access to inside hosts?

Let's say you want to have:

DMZ security 50

inside security 100

outside security 0

On the DMZ interface is the "DMZ_NET", inside is the "INSIDE_NET" and the outside is the "OUTSIDE_NET" and you wanted this:

INSIDE_NET can access the outside network (aka the Internet)

DMZ_NET can access the outside network (aka the Internet)

OUTSIDE_NET cannot access either the DMZ_NET or the INSIDE_NET.

DMZ_NET cannot access the INSIDE_NET.

and you wanted to use ACLs.

Would you use nat/global or static (one to one subnet xlate like static (dmz,outside) DMZ_NET DMZ_NET netmask to allow the DMZ net to access outside with it's own IPs and put an ACL with permit ip any any? Would that work and also not allow the DMZ_NET to access the INSIDE_NET since there is no static or nat/global from the DMZ_NET to the INSIDE_NET?

Now if you did want to allow one host on the DMZ_NET to access a host on the INSIDE_NET would you do a static for that one host, say something like:

static (inside,dmz) DMZ_HOST DMZ_HOST netmask

Would the DMZ host have access at this point to the INSIDE_HOST (because your ACL has permit ip any any or simply because of the static with no regard to the ACL????)

I assume you have to have the static and the ACL entry, but in this case the ACL entry has permit ip any any. So would the DMZ_HOST have complete access to the INSIDE_HOST on all ports? It seems like it would be difficult to allow selective traffic from the DMZ_HOST to the INSIDE_HOST (e.g. only allowing TCP 3389 from the DMZ_HOST to an INSIDE_HOST) and also at the same time allow everything from the DMZ out to the OUTSIDE_NET (aka Internet). Am I missing something?


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