User`s guide

USER’S GUIDE
50 SFVRA Connection Manager
SPX Protocol
SPX Protocol is optionally used by NetWare applications requiring guaranteed, in-sequence
delivery of packets by a connection-oriented service. Each end of an SPX connection sends keep-
alive packets, identified as <SYS> packets, to monitor the status of the connection.
The SPX protocol ensures connection integrity by exchanging a keep-alive packet between the
connection end-points, once every 6 seconds. If an SPX keep-alive packet is received that is destined
for a remote user and no connection exists to the user, a connection would have to be established
to deliver the packet. The keep-alive packets are handled using the same approach being used for
server watchdog request packets. With SPX spoofing enabled, a keep-alive is generated internally
and delivered to the local endpoint as if the packet was sent by the remote endpoint. This satisfies
the local endpoint without causing a connection to be established. To allow an SPX connection to
timeout the keep-alives are forwarded over the WAN when a connection already exists. In
addition, an SPX spoofing duration time T can be specified. When the connection is down to a user
and a keep-alive is received that should be forwarded to this user, a keep-alive will be spoofed for
T amount of time. After T amount of time, the keep-alive will be filtered without generating a keep-
alive response. The duration timer T starts when a user is disconnected and is reset each time a new
connection is established.
Some of these <SYS> packets are overloaded in that they are not just keep-alive packets but are
control packets needed for the application to run successfully and hence have to be routed like
regular SPX data packets. If any NetWare application does not seem to work across WANs, it may
be because of the mishandling of these <SYS> packets and can be traced by disabling SPX keep-
alive spoofing.
This above described implementation is followed for keep-alive packets received over the LAN and
the WAN. If a keep-alive is received over the WAN and it is determined that a spoofed keep-alive
should be generated, it will be returned over the same WAN connection on which it was received.
The parameters for SPX spoofing are configured for each user. The SPX spoofing option can be
enabled or disabled. By default the option is enabled. When disabled the SPX keep alives are routed
without any special handling. If the option is enabled the SPX spoofing duration time T is specified
in minutes. The default is set to 120 minutes.