I looked at this:
http://www.experts-exchang
and it makes perfect sense to me. We are doing similar stuff:
static (inside,outside) tcp interface 2121 [internal IP of hosted server] ftp netmask 255.255.255.255 0 0
access-list OUTSIDEACL permit tcp host [ip of our office] host [external IP avalaible on pix] eq 2121
ie we map a port (2121 in this case) on the external ip of the pix throught to a different port (21 here) on a specific intenal ip at our dedicated hosting.
However we also have specific external-to-intenal ip mappings. Like:
static (inside,outside) [available external IP on pix] [internal IP of hosted server] netmask 255.255.255.255 0 0
Then we allow certain ports through for that mapping (sometimes only allowing access from specific ips as is sensible for ssh):
access-list OUTSIDEACL permit tcp any host [available external IP on pix] eq www
access-list OUTSIDEACL permit host [ip of our office] host [available external IP on pix] eq ssh
Super. But my boss now wants to mask those ports. So that ssh(22) or ftp(21) are not available on the outside but perhaps 2121 and 2222 are. But I am not able to work out the syntax for this port mapping when we have a dedicated external IP for an inernal server. I can only do "pass through" ports. I would guess for the access-list it would be:
access-list OUTSIDEACL permit host [ip of our office] [ecernal port to connect on] host [available external IP on pix] eq [internal port to forward to]
But this does not actually forward the port, it just allows the traffic. How do you forward one port to another if you have all traffic for an external ip pushed to an internal ip. Not possible? Cheers, D.
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I think I get it. But I would have to map each port individually in this way even if I wanted most ports to "pass through" without being changed. Is that correct? By which I mean: there is no way to map ip to ip to allow simple pass-though traffic AND say but map this port to this other port in one case.
We use quite a lot of ports an this would make our fire wall rules much longer. But, if that's what we have to do...
So to hide the real ports I need to remove the IP to IP mapping and add IP:port to IP:port mapping for each port we need as well as add an access rule for each? Can you confirm that the access rule for your example would be along the lines of:
access-list OUTSIDEACL permit host [ip of our office] [exernal port to connect on] host [available external IP on pix] eq [internal port to forward to]
OR (where 4.3.2.1 = our office; and 1.2.3.4 = an external pix IP):
STATIC (INSIDE,OUTSIDE) TCP 1.2.3.4 2222 192.168.1.x 22
access-list OUTSIDEACL permit host 4.3.2.1 2222 host 192.168.1.x eq 22
As you will be changing the dynamics of the external interface you will need to perform a clear xlate.
Not having seen your original config, you will also need to consider the ordering of the lines within your ACL. For example, a one-to-one static mapping allowing all tcp traffic from external to internal address would negate any following rules allowing only particular ports to the same destination.
InteraX: I follow. It's not as bad as it seems then.
keith_alabaster: Thanks, I could easily have missed using clear xlate.
I'm think I'll be removing the one-to one in favour of specific ip and port mapping. However, are you saying a one-to-one static would override any following rules? Is this a case of first that matches applies? In which case can I have rules for those ports I need to forward/change before a one-to-one and so not have to map every port I need?
Eg If I need to map 21, 22 and 80, but only mask 22 into 2222 I could have:
STATIC (INSIDE,OUTSIDE) TCP 1.2.3.4 2222 192.168.1.2 22
STATIC (INSIDE,OUTSIDE) TCP 1.2.3.4 192.168.1.2
and this would map external port 2222 to internal port 22 but all other ports would be passed through Unaffected. (I guess this would not black external port 22 from accessing internal port 22 though defeating the object of the exercise - is there a block rule?). D.
So there is a way to block as well as allow! Could you give me a clue on the syntax? I just assumed it was block unless you allowed traffic. It somehow seemed silly to have allow rules you would need to then block again (before now).
Is it just
access-list OUTSIDEACL block tcp any host [available external IP on pix] eq 22
that I need? (Sorry, I have no pix to mess with. Just a live service. If I mess it up I'll get my fingers chopped off!)
Yes, but is it possible to say (pseudo rules):
Access list:
block port 22 on [external ip] going to [internal ip]
Allow port 2222 on [external ip] through to port 22 on [internal ip]
Allow ALL traffic on [external ip] throught to [internal ip]
NAT:
Map port 2222 on [external ip] to port 22 on [internal ip]
Map [external ip] to [internal ip]
If the pix matches and allows block IN ORDER, this should allow me to map 2222 to 22, pass all other traffic straight through, but block access on port 22. Shouldn't it? Am I getting this entiely wrong or finally getting the idea?
Well, I'll give this a go when I can. As I havn't pix I can test these things on I will have to wait for a go ahead from my boss that he wants me to try this out. At least I know it's possible. I have no idea how to re-order rules without removing and re-adding them so I'll probably be asking questions about that next... Thanks to all.
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Answer for Membership
by: InteraXPosted on 2006-09-25 at 03:52:13ID: 17590995
Hi daveky,
The full syntax of the static command can e found at http://www.cisco.com/en/US
It is possible to map ports. Basically, the command for PIX V6.3 should read as follows.
STATIC (INSIDE,OUTSIDE) TCP OutsideIP OutsidePort InsideIP InsidePort
Good Luck,
Chris