5-24 Administrator’s Handbook
For PPTP negotiation to work, TCP packets inbound and outbound destined for port 1723 must be allowed.
Likewise, for ATMP negotiation to work, UDP packets inbound and outbound destined for port 5150 must be
allowed. Source ports are dynamic, so, if possible, make this flexible, too. Additionally, PPTP and ATMP both
require a firewall to allow GRE bi-directionally.
The following sections illustrate a sample filtering setup to allow either PPTP or ATMP traffic to cross a firewall:
•"PPTP example" on page 5-24
•"ATMP example" on page 5-27
Make your own appropriate substitutions. For more information on filters and firewalls, see Chapter 10,
“Security.”.
PPTP example
To enable a firewall to allow PPTP traffic, you must provision the firewall to allow inbound and outbound TCP
packets specifically destined for port 1723. The source port may be dynamic, so often it is not useful to apply
a compare function upon this portion of the control/negotiation packets. You must also set the firewall to allow
inbound and outbound GRE packets, enabling transport of the tunnel payload.
From the Main Menu navigate to Display/Change IP Filter Set, and from the pop-up menu select Basic Firewall.
Select Display/Change Input Filter.
Display/Change Input Filter screen
Select Input Filter 1 and press Return. In the Change Input Filter 1 screen, set the Destination Port information
as shown below.
Main
Menu
System Filter
Sets Display/Change
Filter Set
Configuration Basic
Firewall
+--#----Source IP Addr----Dest IP Addr------Proto-Src.Port-D.Port--On?-Fwd--+
+---------------------------------------------------------------------------+
| 1 0.0.0.0 0.0.0.0 TCP NC =2000 Yes No |
| 2 0.0.0.0 0.0.0.0 TCP NC =6000 Yes No |
| |
+---------------------------------------------------------------------------+