topic Re: Unable to Port Forward to inside object host in Network Security

Unable to Port Forward to inside object host

tbrendle — Tue, 12 Mar 2019 02:03:03 GMT

The physical setup is a little odd as the ASA is connected to the LAN interface of a SOHO wireless router/firewall, and I'm wondering if that is the issue with the port forwarding failures. There's a remote-pc that requires vnc access to connected to the asa.

The SOHO router is the asa's gateway @ 192.168.2.1 and is configured to port forward tcp:5900 (vnc) to the ASA's outside address (192.168.2.254).

I have also tried setting 192.168.2.254 as a dmz on the soho router, but to no avail.

Here's the ASA's relavent config lines:

interface Vlan10

nameif outside

security-level 0

ip address 192.168.2.254 255.255.255.0

interface Vlan20

nameif inside

security-level 100

ip address 10.2.2.1 255.255.255.0

object network Remote-PC

host 10.2.2.27

object service vnc

service tcp source eq 5900 destination eq 5900

description vnc server/viewer

object service rdp

service tcp source eq 3389 destination eq 3389

description Remote Desktop (if vnc crashes)

object-group network inside-net

description VLAN 20 Inside IP Range

network-object 10.2.2.0 255.255.255.0

access-list outside_access_in extended permit object vnc any object Remote-PC

access-list outside_access_in extended permit object rdp any object Remote-PC

nat (inside,outside) source dynamic inside-net interface

object network Remote-PC

nat (inside,outside) static interface service tcp 5900 5900

policy-map type inspect dns preset_dns_map

parameters

message-length maximum client auto

message-length maximum 512

policy-map global_policy

class inspection_default

inspect dns preset_dns_map

inspect ftp

inspect h323 h225

inspect h323 ras

inspect ip-options

inspect netbios

inspect rsh

inspect rtsp

inspect skinny

inspect esmtp

inspect sqlnet

inspect sunrpc

inspect tftp

inspect sip

inspect xdmcp

inspect icmp

class class-default

user-statistics accounting

service-policy global_policy global

-----------------------------------------------------

Thanks in advance for any help!

Re: Unable to Port Forward to inside object host

Jouni Forss — Wed, 26 Jun 2013 09:15:40 GMT

Hi,

Theres a problem with NAT rule ordering and ACL

Do the following changes

NAT

no nat (inside,outside) source dynamic inside-net interface

nat (inside,outside) after-auto source dynamic inside-net interface

In the above we move the NAT rule from Section 1 to Section 3 effectively changing it to be a lower priority NAT configuration rule. In its current form its overriding the Static PAT and preventing it from working.

ACL

Problem with the ACL is that you define the service port for RDP and VNC as both the source and destination. The remote connections wont be coming from the same source port as the destination port is. So basically you dont define any source port, only the destination port.

Old

no access-group outside_access_in

no access-list outside_access_in extended permit any object Remote-PC

no access-list outside_access_in extended permit object rdp any object Remote-PC

no object service vnc

no object service rdp

New

object service RDP

service tcp destination eq 3389

object service VNC

service tcp destination eq 5900

access-list outside_access_in extended permit object RDP any object Remote-PC

access-list outside_access_in extended permit object VNC any object Remote-PC

access-group outside_access_in in interface outside

Hope this helps

Please do remember to mark the reply as the correct answer if it answered your question.

Ask more if needed

- Jouni

Unable to Port Forward to inside object host

tbrendle — Wed, 26 Jun 2013 10:35:22 GMT

Brilliant! That worked perfectly.

I really appreciate the detailed explanation of the changes. It makes total sense now.

5 star reply!

Thank you Jouni.

Unable to Port Forward to inside object host

tbrendle — Mon, 01 Jul 2013 15:42:18 GMT

Well, this is awkward. I seemed to have broken it. I reapplied the config based on your fix (which worked before) and it's not allowing the connection now. I'm assuming it has something to do with the NATing since I've set up an L2L. The 2nd line is for an L2L VPN, which may be the problem.

Config:

nat (inside,outside) source dynamic any interface

nat (inside,outside) source static inside-net inside-net destination static Brazos-Net-All Brazos-Net-All

nat (inside,outside) after-auto source dynamic inside-net interface

object network inside-net

subnet 10.2.2.0 255.255.255.0

object service RDP

service tcp destination eq 3389

object service VNC

service tcp destination eq 5900

object service WEB-VNC

service tcp destination eq 5800

access-list outside_access_in extended permit object RDP any object Remote-PC

access-list outside_access_in extended permit object VNC any object Remote-PC log debugging

access-list outside_access_in extended permit object WEB-VNC any object Remote-PC

access-group outside_access_in in interface outside

----

Thanks in advance for any help!

Unable to Port Forward to inside object host

Jouni Forss — Mon, 01 Jul 2013 15:47:26 GMT

Hi,

Provided this NAT configuration still exists (with the "host" statement inside the "object network")

object network Remote-PC

host x.x.x.x

nat (inside,outside) static interface service tcp 5900 5900

Then you again have a Dynamic PAT rule that is overriding the Static PAT (Port Forward)

Unless you have gotten more inside networks that need Dynamic PAT then simply remove this configuration

no nat (inside,outside) source dynamic any interface

- Jouni

Re: Unable to Port Forward to inside object host

tbrendle — Mon, 01 Jul 2013 16:02:32 GMT

Yep, you nailed it again!

What is the best way to add dynamic PAT for multiple ports to that host?

(ex: tcp/5900, 5800, 3389).

Unable to Port Forward to inside object host

Jouni Forss — Mon, 01 Jul 2013 16:12:37 GMT

Hi,

Sadly there is no easy way that wouldnt generate more configuration. For each port you want to forward to a host you will have to configure a separate NAT configuration

So you would have to add something like this

object network Remote-PC-RDP

host x.x.x.x

nat (inside,outside) static interface service tcp 3389 3389

I guess it would be good to come up with some good naming convention if you are configuring multiple ports.

If you want to rename an existing "object network" then you can do for example

object network rename

This will change the name of an existing "object network"

As I saidf, there is no clean and easy way to configure multiple ports as you CANT use "object-group service" in any NAT configurations.

- Jouni

Re: Unable to Port Forward to inside object host

tbrendle — Mon, 01 Jul 2013 16:21:05 GMT

I was hoping for the object group service answer. Lol.

The new Network Objects are created for each static PAT and all is working beautifully now.

Thank you again, Jouni!