Friday, November 7, 2014

How Network Discovery Works - Part 1

How Network Discovery works - Part 1

In the early 90's, HP Network Node Manager has been one of the pioneers in utilizing a network discovery algorithm to identify network nodes and their topology. The discovery algorithm has been registered as a US Patent by HP.

Basically, in NNM 3.0 till NNM 7.x the discovery algorithm used to work as follows:
  • The NNM server own IP configuration was used to determine the discovery targets ( based on IP
    address, subnet mask and default gateway).
  • A ping sweep has been initiated to identify all responding IP addresses
  • All responding addresses were queried via SNMP to make sure they can communicate with NNM
  • All the nodes that responded to SNMP were queried for interesting tables:  System, ARP, Interfaces.
  • Node types and their vendor have been identified according to their response to SNMP system ObjectID (Router, Bridge, Computer) 
  • Nodes that were identified as Routers were queried for their routing tables.
  • Then the process of identifying new devices was repeated for any additional IP segment discovered by the previous step
Network administrators could control the network discovery by placing filters and various
limits to ensure it would not run forever and discover the entire Internet
(in 1995 it was still possible :) ).

The NNM map used to look like the picture below:

As networks became more complex and new technologies and protocols were added, this algorithm has been modified and adapted to handle VLANs, CIDR and various Layer 2 technologies, however it became too limited to handle newer technologies such as virtual interfaces and multi-link protocols (EtherChannel, 
MLT, SMLT etc) and also it was quite challenging to display the new topology using the outdated map based on old X/Motif technology (later ported to Windows as well).

In "How Network Discovery Works - Part 2" I will discuss the latest advances in this field

Yigal Korolevski, KMC Technologies http://www.nms-guru.com


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