|Microwave Data Systems
LEDR Point-to-Point Microwave Radio
Protected NSD Operation in Version 4.2.0 Firmware
May 17, 2001
The LEDR microwave radio provides a out-of-band service channel which may be used for network management. The service channel operates in an out-of-band channel over the air and through the Ethernet interface between co-located radios.
The service channel uses the Unit ID's assigned to radio to deliver network management packets. The LEDR software provides Network Self-Discovery (NSD) which allows the radios to discover one another and build a network table which consists of the Unit ID, IP address, relative location, and the owner's name for each radio that it can "see.” This includes all LEDR radios that are part of the same RF or Ethernet network, and that share the same group (see the “group” command in the radio manual for details.) Each radio’s IP routing table is updated with an IP host route to each radio that it can see. The network table can be viewed by executing the command "network" and the routing table can be viewed by executing the command "route print".
In order to aid the user in setting up IP routing within the network, the LEDR software provides a Proxy ARP feature. When a device, such as a PC, attempts to send an IP packet to a remote LEDR radio, the LEDR radio(s) connected to the primary network, known as the gateway radio, will proxy ARP for the remote radio causing the PC to send the IP packet to the gateway radio's Ethernet address. In the case of a protected pair connected to the primary network, both radios in the protected pair will proxy ARP for the remote radio.
IP Configuration for Protected links
The LEDR software provides a basic IP configuration including IP address, netmask, default gateway, and default port. When the gateway radio is part of a protected pair the remote radios can still only have one default IP gateway. One of the two protected radios connected to the primary network must be selected as the IP gateway. All of the remote radios will be configured with the default gateway being the selected radio.
In addition to Network Self-Discovery packets, the LEDR software passes Protected NSD packets which are helpful in the case where the gateway protected radio fails. The Protected NSD packets contain information which provide the remote radios with the IP address and Unit ID of the gateway radio's sibling. In the case where the gateway radio fails, the remote radios will switch over to use the sibling as their IP gateway.
Issue with Protected NSD
The Protected NSD packets have been found to cause intermittent problems wherein the gateway radio, or its sibling, stops transmitting and responding to Ethernet packets. The result is that the affected radio, although it continues to pass payload data without interruption, is no longer accessible by SNMP, Telnet, ping, TFTP, and the web browser interface. To prevent this, under firmware version 4.1.0, MDS strongly suggests disabling Protected NSD by executing the command "rdnt nsd off."
The repercussion of disabling Protected NSD is that connectivity for network management can be lost if the transceiver designated as the gateway were to fail; at that point, all IP packets to and from the radios beyond the gateway radio would stop flowing. This results in the loss of all SNMP, Telnet, ping, TFTP and browser communications with the radio network and any attached devices that use the radio’s service channel for their network management.
The workaround, in the unlikely event of a hardware failure in the gateway radio, is to change the IP address of the sibling radio to the IP address of the failed gateway radio. The other option, which is considerably more work, is to individually log into all radios downstream from the gateway and change their default IP gateways to the IP address of the remaining radio at the gateway location.