Owner`s manual

139
Application Level Gateways
There are certain applications that NAT and Firewall
configurations cannot manage. In many cases, ALGs
(Application Level Gateways) are needed to translate and
transport packets correctly. An ALG provides a service for a
specific application such as FTP (File Transfer Protocol).
Incoming packets are checked against existing NAT rules or
Firewall filters, IP addresses are evaluated and detailed packet
analysis is performed. If necessary, the content of a packet is
modified, and if a secondary port is required, the ALG will open
one. The ALG for each application does not require any
configuration.
ALG support is provided for the following applications. If support
is required for additional applications, security triggers can be
configured for these.
Application TCP Port UDP Port
AIM (AOL Instant Messenger) 5190 N/A
FTP (File Transfer Protocol) 21 N/A
IKE (Internet Key Exchange) N/A 500
ILS (Internet Locator Service) 389 (+1002) N/A
MSN (Microsoft Networks) 1863 N/A
PPTP (Point-to-Point Tunneling
Protocol)
1723 N/A
RSVP (Resource Reservation
Protocol)
N/A N/A
L2TP (Layer 2 Tunneling Protocol) N/A 1701
SIP (Session Initiation Protocol) 5060 5060
Security Trigger
A security trigger can be defined for applications that are not
supported by the ALGs listed above. A security trigger allows
the firewall to dynamically open and close secondary ports
associated with a particular application and to specify the
maximum length of time the port remains open.