LXI Discovery

One of the differences presented by Ethernet connected devices is that of discovering the IP address of an LXI device. Since it is impossible to predict the IP address that a customer wishes to use for any particular device, and it could cause problems if an LXI device were to be shipped set to a fixed IP address, most products are shipped configured to obtain their IP address from a system DHCP server.

Should no DHCP server be present the device should fall back to an automatic IP address selection. In both cases the user cannot know in advance what that IP address might be, although in the Auto-IP case it is sufficiently known for discovery to be practicable.

The LXI Specification specifies two discovery protocols. LXI products all provide a mechanism based on the VXI-11 discovery protocol and an mDNS discovery protocol. Pickering devices include both protocols.

Neither mechanism is capable of resolving the IP address in all network circumstances, but with a little care either should be capable of discovering the LXI device. An LXI Discovery Tool is also available from the LXI web site here which provides many advanced features to aid discovery in a wide range of circumstances.

Both National Instruments (c) Measurement and Automation Explorer (MAX) and the Keysight (formerly Agilent) (c) Connection Expert (ACE) are capable of discovering LXI devices, examples are provided in the manuals delivered with Pickering products. Pickering also provide some discovery tools on the distribution disk for those without an NI or Keysight/Agilent installation. The LXI Consortium have made a discovery tool available from their web-site: LXI Discovery tool

Pickering also provide some discovery tools at the following locations:

http://www.pickeringtest.info/downloads/drivers/Sys60/

http://www.pickeringtest.info/downloads/Utils/

Common Difficulties

Some users have experienced difficulties discovering LXI devices, most of these have been caused by the instrument and user computer being connected to different sub-nets of the network. A search on the internet will soon uncover many pages explaining network configuration, we shall not try to explain it here. Resolution of that issue normally results in quick and easy discovery.

These are some situations users have reported to Pickering:

Second Internet Connection (eg Wireless connection on a Laptop Computer)

There are a number of scenarios where this situation can arise. For example a laptop computer with an LXI product connected using a cross-over ethernet cable, or a computer with a second ethernet connection via an additional ethernet card, or a computer with a single ethernet connection but with virtual ethernet cards created by a virtualization products.

In these cases the LXI device may not find a DHCP server and will therefore fall back to an Auto-IP address in the range 169.x.x.x. The computer however may obtain an IP address though another ethernet port in a different range, perhaps 192.168.x.x. Under these circumstances the discovery mechanisms are unlikely to succeed. In some cases this is caused by the gateway address of the LXI connected port being set to the other network address range.

The easy solution in the above case is to disable the other ethernet connections and so force the computer to also select an Auto-IP address; with both devices on the same sub-net, discovery will work. In the case of a laptop, disable the wireless ethernet connection.

To ascertain the IP address of your computer, open a command window and type 'ipconfig'. This will usually provide a listing that includes the IP address of the computer. On a Linux system, use 'ifconfig'.

To view the gateway addresses on your computer type 'route print' to obtain a listing of the IP addresses and gateway addresses assigned on the PC.

Firewall

A firewall is blocking access, once again the easy solution is to disable the firewall, not always an acceptable solution, or to modify the firewall to permit the connection. In some cases we have encountered a 'hidden' firewall contained in anti-virus software.

Forgotten IP Address

An LXI instrument has been set to a fixed IP address, but the user doesn't know the address; in this case the only real solution is to perform a factory reset on the LXI device to restore it to the default DNS method of IP address selection. On a Pickering LXI device this can be performed by holding the rear-panel reset button depressed for a period of 5 seconds, on release the product should re-start with factory defaults set, hence DHCP address setting.

Solutions

It is not always possible for a user to resolve the problem alone, in such cases the help of the local IT department should be sought to help diagnose the problem and so arrive at an acceptable solution. The LXI Consortium publish a set of guides on using LXI instruments, including a guide to assist IT departments that can be found here

Programmatic Discovery

Pickering software drivers include discovery as part of the API, thus allowing programmers to determine the IP address of Pickering LXI products at run-time. Refer to API documentation and example programs for details of this facility.

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