System Timeout; Https - ZyXEL Communications ZYWALL USG 20 Manual

You have disabled that service in the corresponding screen.
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The allowed IP address (address object) in the Service Control table does not
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match the client IP address (the ZyWALL disallows the session).
The IP address (address object) in the Service Control table is not in the allowed
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zone or the action is set to Deny.
There is a firewall rule that blocks it.
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43.7.2 System Timeout

There is a lease timeout for administrators. The ZyWALL automatically logs you
out if the management session remains idle for longer than this timeout period.
The management session does not time out when a statistics screen is polling.
Each user is also forced to log in the ZyWALL for authentication again when the
reauthentication time expires.
You can change the timeout settings in the User/Group screens.

43.7.3 HTTPS

You can set the ZyWALL to use HTTP or HTTPS (HTTPS adds security) for Web
Configurator sessions. Specify which zones allow Web Configurator access and
from which IP address the access can come.
HTTPS (HyperText Transfer Protocol over Secure Socket Layer, or HTTP over SSL)
is a web protocol that encrypts and decrypts web pages. Secure Socket Layer
(SSL) is an application-level protocol that enables secure transactions of data by
ensuring confidentiality (an unauthorized party cannot read the transferred data),
authentication (one party can identify the other party) and data integrity (you
know if data has been changed).
It relies upon certificates, public keys, and private keys (see
589 for more information).
HTTPS on the ZyWALL is used so that you can securely access the ZyWALL using
the Web Configurator. The SSL protocol specifies that the HTTPS server (the
ZyWALL) must always authenticate itself to the HTTPS client (the computer which
requests the HTTPS connection with the ZyWALL), whereas the HTTPS client only
should authenticate itself when the HTTPS server requires it to do so (select
Authenticate Client Certificates in the WWW screen). Authenticate Client
Certificates is optional and if selected means the HTTPS client must send the
ZyWALL a certificate. You must apply for a certificate for the browser from a CA
that is a trusted CA on the ZyWALL.
ZyWALL USG 20/20W User's Guide
Chapter 43 System
Chapter 39 on page
645