STATIC NAT PROBLEM

Question

Hi All,
We are having a problem with a static NAT statement and or ACL not allowing traffic to the port configured to the inside host on the LAN.
NETWORK SETUP
We have a 3CX IP PBX behind a Pix firewall and need remote hosts to be able to connect to the 3CX over the 3CX tunnel protocol that uses port 5090. 3CX internal IP Address is 172.16.0.254 and the port it is listening on for the tunnel traffic is 5090. We have configured static NAT to the 3CX which is listening on port 5090 and created the ACL and applied this to the Outside interface. 3CX tunnel protocol uses a mixture of TCP and UDP so we have these both configured. Here are the various lines of configuration.
access-list Outside_In extended permit tcp any host 172.16.0.254 eq 5090
access-list Outside_In extended permit udp any host 172.16.0.254 eq 5090
static (Inside,Outside) tcp interface 5090 172.16.0.254 5090 netmask 255.255.255.255
static (Inside,Outside) udp interface 5090 172.16.0.254 5090 netmask 255.255.255.255
access-group Outside_In in interface Outside
ISSUE
We have configured static NAT to the 3CX which is listening on port 5090 and created an ACL to permit inbound traffic to the 3CX. Inbound traffic is not traversing the firewall and therefore not reaching the 3CX on the inside LAN.
TROUBLE SHOOTING SO FAR
We have tried a number of different ACL and NAT configurations, but the above configs are not permitting the traffic through the firewall. We have done a number of captures on the firewall and we can see the traffic from remote hosts getting to the Outside interface, but not traversing to the Inside interface and therefore not reaching the 3CX on the inside LAN. The xlate shows the static NAT entry correctly.
Any suggestions anyone??
Regards,

Answer 1

Hi,
If you are doing a Static NAT or Static PAT towards the Internet on your ASA or PIX, this is how the different firewall software versions behave
Software 8.2 and earlier: When you configure a Static NAT / Static PAT and want to allow traffic from the Internet to the NATed host, you use the NAT IP address as the destination IP address in the ACL attached to the "outside" interface you are using.
Software 8.3 and later: NAT and ACLs changed in the 8.3 software and in those software levels you are required to use the actual real IP address of the host in the ACLs you configure. Using the NAT IP address in the newer software levels wont work anymore.
As you mentioned your software level to be 8.0 we can see that you need to use the NAT IP address as the destination address of the "outside" interface ACL.
I guess you could try for example
access-list Outside_In permit tcp any interface Outside eq 5090
access-list Outside_In permit udp any interface Outside eq 5090
You can also use the "packet-tracer" command like I mentioned above to simulate what the firewall would do to the traffic.
The command tested could be for example
packet-tracer input Outside tcp 1.2.3.4 1234 5090
The only situation where I could see the need to use the real IP address in the ACL statement of the "outside" interface would be if you had a L2L VPN / Site-to-Site VPN configured between your firewall and the remote end. But as I cant see your configuration I dont know if thats the case. Though since you have configured Static PAT to use the public IP address of your firewalls "outside" interface it would lead me to believe that you are trying to open/share this service from the LAN device to the Internet.
Guess you could next try the above mention ACL lines I listed and test the traffic again. Also the "packet-tracer" command should tell you if theres any problems with your firewall configurations.
- Jouni