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Security, hacker detection & forensics FAQ

GVC Client

GVC does'nt working behind a Non SonicWall Firewall\NAT device by SonicWALLInstructor
Posted: 10 Mar 06

GVC does not working behind a 3rd party Firewall\NAT device


Overview

This tech note provides more information about issues encountered when trying to connect to your corporate Office SonicWall Firewall using GVC Client behind a 3rd party Firewall\NAT device (ex Linksys, Dlink, Netgear, etc.)

There are a number of reasons why this might fail. This document will discuss some of the more common reasons and provide some procedures to resolve these issues.

ESP Traffic is Blocked

Problem:

GVC may be run from behind a firewall or other device that allows ISAKMP traffic to pass through, but does not allow ESP traffic to pass through. The DHCP requests that get sent for the virtual adapter are sent down the tunnellike any other traffic and are thus encapsulated in ESP. The ESP packets are simply dropped by the firewall with no indication back to GVC.

Solution:

To work around this problem, GVC is enabled to detect a NAT device in the middle. When GVC detects a NAT
device, it encapsulates all ESP traffic (including DHCP packets) using the UDP header. The UDP header uses the
same port as ISAKMP control traffic. Therefore the Peer must separate the IKE control traffic from the data traffic.

1. To configure the NAT traversal setting from the client, select the Connection in GVC and then select File -> Properties.

2.Select the Peers tab and then select the appropriate PEER (head-end firewall) and choose Edit.

3. Next choose NAT Traversal and select Forced On.[/b]


NAT Traversal UDP Encapsulated ESP Traffic is blocked.

Problem:

Occasionally GVC may be run from behind a NAT device that improperly handles NAT traversal packets (ESP
packets encapsulated in ISAKMP). These packets are discarded by the NAT device without any notification sent
back to GVC.

Solution:

To work around this problem, set GVC never to perform NAT traversal. This means that ESP traffic will not be
Encapsulated in UDP. In order for this to work, the NAT device must be in æIPsec pass-throughÆ mode. This mode
will prevent multiple GVC clients running simultaneously behind a single NAT device.

 
To disable NAT traversal in the client,

1. Select the Connection in GVC and then select File -> Properties.

2. Select the Peers tab and then select the appropriate peer (head-end firewall) and choose Edit.

3. Next choose NAT Traversal and select Disabled (see Screenshot 7 below).
 
EXTRA SUGGESTIONS:

Update the GVC Client  

Starting with version 3.0.0.0 of GVC a new NAT traversal specification is supported that can bypass many NAT devices that improperly handle UDP encapsulated ESP packets.

This is done by switching the port used for ISAKMP from the default 500 to 4500.

Note: See your network administrator for information on how to update to the latest release of GVC and/or the firewall firmware.

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