Local IP address of devices (classic)
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Traditionally, Nexthink Engines read the IP address (or addresses) of a device from the header of the IP packets that they receive from Collector. Indeed, a field called Source IP Address is part of the header of every IP packet. Thus, for Engines that share the same network as their monitored devices, reading the IP addresses of devices from the header of the received IP packets makes perfect sense.
When Engine monitors devices in a different network, the routers between the two networks perform what is known as network address translation (NAT) to IP packets in transit, effectively changing the original source IP address on each packet to the IP address of the router in the destination network. As a result, Engine records the IP address of the router as if it were the IP address of the device that sent the packet.
For example, in the simplified figure above, Engine records the source IP address of all devices behind the router to be the same: 203.0.113.1; that is, the address of the router as seen by Engine.
To alleviate this problem Collector additionally reports the local IP address of devices; that is, the IP address of the device as seen from the local network before any NATting takes place. In the example, the local addresses of the devices are 192.0.2.10-12.
The rules to assign Collectors to Engines can thus be based either on the source IP address, which may be changed in transit as explained, or on the new local IP address, which is never modified by NAT routers.
A single device can have multiple network adapters, each one with a different IP address assigned in the local network. For instance, a laptop may simultaneously have a wired Ethernet connection and a wireless connection to the local network.
In this case, Collector reports the IP address of the adapter that is used to communicate with Engine as the Local IP address.
