Tech Tip for June 2010
By Patrick V. Labayen

Title: Setting Up Sequential or Simultaneous Serial Tunnel for an EDS1100/2100

Question: How do I configure multiple hosts in Connect Mode? Where can I find the configuration setting for sequential or simultaneous connection?

The Hostlist function is the ability to configure more than one remote IP host when configuring a serial tunnel on a Lantronix device server. While a regular serial tunnel means a connection to a single remote IP host, hostlist allows connections to multiple remote IP hosts.
There are two types of hostlist connections: sequential and simultaneous.
Sequential hostlist, similar to what's available in the CoBOS family of device servers, starts a TCP socket connection to individual entries in the hostlist, starting with the first IP host on the list.
The device server will attempt a connection to each IP host sequentially until it succeeds making a TCP socket connection to a host. Should the established connection drop, then the device server will start the same sequential connection attempt from the beginning of the list until it finds the next available connection.
Simultaneous hostlist, similar to what's available in the MSS family of device servers, makes concurrent TCP socket connections to all listed remote IP hosts in the hostlist. This type of connection permits the device server to 'broadcast' the same message to multiple IP endpoints. These connections are virtually simultaneous.
Starting in firmware version 5.0, which was introduced in the EDS1100 and 2100, Evolution OS is capable of making multiple outbound TCP socket connections to up to 16 remote hosts on the network. Depending on configuration setting, Evolution is capable of making sequential or simultaneous hostlist connections.
To configure connect mode with multiple hosts, follow the bulleted sequence below.

• Log into the EDS WebManager.
• Click on the 'Line' item in the left-hand navigation menu.
• Select the line you want to configure the host list for
• Select configuration
• Verify that the line state is 'Enabled', and Protocol is set to 'Tunnel'.
• Configure the rest of the serial line parameters as needed.
• Click 'Submit' after all changes have been made.
• Click on the 'Tunnel' item on the left-hand menu, then 'Connect Mode'
• Enter the remote host IP address and Port number in the fields for Host 1
• Choose the protocol and TCP Keepalive value you wish to. A field for Host 2 appears while a value is being entered in Host 1.
• Enter your next remote host IP address and Port number in the Host 2 field
• Choose a protocol and TCP Keepalive value. Similarly, a field for Host 3 appears while a value is being entered in Host 2 fields.
• Add another host or click 'Submit' if you are done.

When Host 2 fields are being configured, Host 3 field and the 'Host Mode Radio Button' will appear and become available for configuration. 'Host Mode' will have selections for 'Sequential' or 'Simultaneous' style connections.
The Host Mode selection will not be available if only one Host is being configured in Connect Mode.
The default 'Host Mode' setting is 'Sequential'. Choose the 'Simultaneous' radio button to make concurrent TCP socket connections to the IP hosts in the hostlist and click 'Submit'.
Simultaneous connections will happen at approximately the same time to all the configured hosts.

Sequential connect mode will attempt a connection to the first configured host in the list. If the connection fails, then the next listed host is attempted. The attempts will continue until a successful connection is made with a host. If a successful connection should drop, the process begins again with the first host on the list.
Configure the host list with the same steps as explained above, except, select 'Sequential' in the 'Host Mode' radio button instead of 'Simultaneous'. This is the default multiple host connect mode.
Host List Promotion or changing the priority of the configured host is possible in Sequential or Simultaneous connect mode. The gray up-arrow icon next to the Host # can be clicked to move the host up in the list.
The screenshot below illustrates the fields described above:

As of this writing, Multiple Host Connect Mode is discussed in detail starting near the bottom of PDF page 59 in the online User Guide, available here.