User Guide

NETNode Operations Guide
Commercial in
Confidence
IP Mesh Systems
000-130
R1.8 2015-07-24
Commercial in
Confidence
Page 2-42
packet contains a list of serial numbers of the nodes which are linked across the radio
network.
If a NETNode detects this packet arriving at a physical port with the same serial number as
itself then the port is blocked unless this is the lowest IP address (if the interlink IP address
is set), then lowest serial number and then the lowest port number in the system. The port
will remain blocked for an additional 30s after the condition is removed. Port probe packets
continue to be sent while the port is blocked.
This prevents IP loops forming by shutting off the physical port of the NETNode to and from
the units’ main MAC address and VLAN addresses. This may be used to an advantage – for
example multiple NETNodes or a single NETNode (using both ports) can be connected to the
same IP backbone providing redundancy if unit or one connection fails.
Note: Port blocking is only effective over a single MESH network. For multiple networks
which contain a loop, routers with Spanning Tree Protocol may be used.
MAC Address Blocking 2.13.1
NETNodes also provide a secondary method of blocking loops.
If a packet which has the same source MAC address arrives via multiple ports (including the
radio interface), then any packet with this source MAC address is blocked for 5s and until the
condition is cleared.
2.14 Interlink Mode
Usually, IP networks do not allow multiple routes from an IP source to an IP destination
address. This precludes multiple nodes to be connected to the same IP backbone network.
For example in a city it is often advantageous to have multiple high points on the same mesh
all connected to the same IP backbone. In this example connection of two NETNodes onto
the same IP backbone would cause a loop to be created in the network.
In practice each NETNode identifies this network loop occurrence (same MAC address
appearing on multiple ports) and blacklists the entry for 30 seconds, to prevent this
happening.
But, it can be extremely useful to be able to connect multiple NETNodes to the same
backbone. For example, a city Mesh system may have two nodes on two different buildings.
In this example it may be that a mobile node is only served by the one of the two nodes (for
example Mesh #1 in the diagram below), and if this not the node connected to the backbone
then IP forwarding over the radio link would have to take place. This reduces the overall
network capacity; as the hop means information has to be sent twice over the radio network.
Step 1: Understanding Interlink Operation
Interlink mode replaces the radio links between the mesh nodes on the backbone with an IP
tunnelling protocol over the IP backbone. To make this IP tunnelling possible one of the
NETNodes acts as a master allowing both tunnelling data and the main IP data through the
Ethernet interfaces while the other nodes act only as slaves just allowing IP tunnelling data
to and from that node.