Question

Cisco PIX - NAT - Multiple IP addresses/ports to one port

Asked by: j_dyer

Assuming a configuration like this:

name 10.0.0.5 Host1
name 10.0.0.6 Host2
name 10.0.0.7 Host3
name 10.0.0.8 Host4
access-list ACL-IN permit tcp any any eq https

I need to set the PIX up so that requests to port 443 on Host1, Host2 and Host4 are all redirected
to port 8443 on Host4, but requests to port 443 on Host3 continue to go to 443 on Host3.

NAT for a single port/address works fine, so I can use one of the following commands (but not both)
with no problems:

static (inside,outside) tcp Host 4 443 Host 4 8443 netmask 255.255.255.255 0 0
static (inside,outside) tcp Host 1 443 Host 4 8443 netmask 255.255.255.255 0 0

If I try to use both commands, I get the 'ERROR: duplicate of existing static' error message back (which
I guess is to be expected).



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Asked On
2004-05-26 at 08:13:45ID21002991
Tags

pix

,

multiple

,

cisco

,

nat

Topic

Network Routers

Participating Experts
1
Points
250
Comments
6

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Answers

 

by: scraig84Posted on 2004-05-26 at 08:17:38ID: 11162524

The Pix is not a load balancer.  You cannot map an internal IP/port to multiple external IP/ports.  Also, with the configuration shown, you are showing all IP's that are presumably on the same subnet and internal.  Yet it appears you are mapping from outside to inside based on your command.  I'm a bit confused at what you are attempting to accomplish.

 

by: j_dyerPosted on 2004-05-26 at 09:01:34ID: 11162854

OK, perhaps my initial question wasn't totally clear...
Where you see '10.0.0.<x>', think of an address in the public ip space - perhaps not the best choice of example
IP numbers... - this system is not using any private ip space.

Normally, a host is made visible on the external interface of the PIX by a
static (inside,outside) Host1 Host1 netmask 255.255.255.255 0 0
command.

What I want to accomplish is to have requests which come in on the external interface for Host1:443, Host2:443 and
Host4:443 get rewritten to Host4:8443.
I don't want to wildcard it though (if such a thing is even possible), since requests on Host3:443 should go straight
through to Host3:443.

I suspect I'm still being as clear as mud here...let me know if I need to clarify things again.

 

by: scraig84Posted on 2004-05-26 at 09:07:05ID: 11162912

That makes sense, but despite my initial confusion, my original statement holds true.  The PIX is not a load balancer.  You cannot statically map multiple external ports to a singe IP and port.  Mapping is a one to one relationship.  

 

by: scraig84Posted on 2004-05-26 at 09:26:34ID: 11163101

Let me add this.  Normally you would not map an internal address to itself like you are suggesting.

Rather than: static (inside,outside) Host1 Host1 netmask 255.255.255.255 0 0

It should be: static (inside,outside) Host1_External Host1_Internal netmask 255.255.255.255 0 0

Also, I'm not certain why you would want multiple IP's on the outside to a single IP on the inside.  That's highly rare.  Can't you direct people to a single published IP?  Why the need for multiple public IP's for a single resource?  If this is for SSL, usually the internal server would also have multiple IP addresses, so you would still have a 1 to 1 relationship.

 

by: j_dyerPosted on 2004-05-27 at 03:46:18ID: 11170037

Well, the mapping is the way it is, because that's the way our hosting company set things up...I'm agree
that it's a bit strange but, since I can blame someone else for that, I will :)

As far as why we're doing this, we're basically migrating some customers who are on multiple different
servers to one server. We have other solutions we can use - this was just the easiest one. Anyway, you've
saved me loads of time trying to find a solution that doesn't exist, so thanks.

One final thing...our config currently has:
access-list ACL-IN permit tcp any host Host2 range 40000 41000

If I wanted to map those connections to a different host, would I need 10000 lines of the form
static (inside,outside) tcp Host2 40000 Host4 40000 netmask 255.255.255.255 0 0
static (inside,outside) tcp Host2 40001 Host4 40001 netmask 255.255.255.255 0 0

or is there some sort of range command I could use to do this instead?

 

by: scraig84Posted on 2004-05-27 at 05:47:33ID: 11170859

Well, I can see why you'd want to perform a migration that way.  That said, if you have control of DNS, drop the TTL of your current DNS records down to a few seconds 3-4 days before the actual migration.  That way, remote DNS servers and clients will only hold the entries in cache for a few seconds.  When you decide to make the DNS change, it will essentially be instantaneous on the client end.  You can then bring your TTL back up to a more reasonable number to save bandwidth.

As for the range, it's nothing I've heard of.  I think the assumption is that if you need to map that many ports, you're best to just map IP to IP and be done with it.  A pretty fair assumption.  The only time you ever sit and map out ports is if two internal hosts are sharing the same external IP address.  If you have that specialized of needs, it would probably be best to just directly map IP's if at all possible.

20120131-EE-VQP-002

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