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[ScreenOS] What Is Session Application Type 78?

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Article ID: KB16017 KB Last Updated: 05 Nov 2020Version: 2.0
Summary:

This article explains what session application type 78 that is shown in "debug flow basic" means.

 

Symptoms:

Debug flow basic shows the following:

session application type 78, name IGNORE, nas_id 0, timeout 1800sec
ALG vector is not attached

ALG vector not attached means that no ALG was invoked for this particular session.

 

Solution:

When a packet with a specific destination port number is seen by the firewall, an ALG (Application Layer Gateway) may be invoked.  If so, then "debug flow basic" will show which of the many ALGs had been hit.

For example, when the FTP ALG is invoked, the following is seen in "debug flow basic".  Notice that the ALG name is FTP:

session application type 1, name FTP, nas_id 0, timeout 1800sec
ALG vector is attached

There are two ways to disable an ALG -- in situations where the firewall's ALG should not be invoked.

  1. Disable the ALG globally.  (i.e, unset alg ftp enable)

  2. Disable the ALG on a per-policy basis.  This is done by specifying the "Application Ignore" option.

When an ALG is disabled on a per-policy basis, then the debug will show application type 78, name IGNORE.

An example of the configuration is as follows:

set policy id 11 from "Trust" to "Untrust" "Any" "Any" "FTP" permit
set policy id 11 application "IGNORE"

 

Modification History:

2020-11-05: Removed broken link; checked article for accuracy

 

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