User Guide

NETNode Operations Guide
Commercial in
Confidence
IP Mesh Systems
000-130
R1.8 2015-07-24
Commercial in
Confidence
Page 2-27
 Other multicast packets are supported by IGMP control and only forwarded to ports
which are members of that group
 Unicast packets are forwarded only to the correct port
Each NETNode keeps an ARP table. This contains the IP, MAC and additionally a port (real
and virtual) of each unicast IP address on the system for the main subnet. The table is built
up by recording the source addresses for both ARP and IP packets entering the NETNode.
There is a separate list for each VLAN on the system.
When a unicast packet arrives on the local subnet, the destination IP address is searched for
in the table, and the packet sent to this port in the table. If no entry is found then this
results in the unit generating an ARP request (who is ...?). Destination IP addresses which
are not on the local subnet are checked against the static and RIP routes and forwarded to
the correct gateway. If this fails then the default gateway address is used.
NETNodes will also send out gratuitous ARP’s when they join the network. This aids network
cohesion.
NETNodes support to following protocols on the local port (‘loc’):
 ARP (LAN and VLAN)
 ICMP ping (LAN and VLAN)
 IGMP (LAN and VLAN)
 RIP v2 (LAN and VLAN)
 DHCP (LAN and VLAN)
 HTTP control (TCP port 80 and 50080)
 TFTP (for upgrades)
 RTSP/RTP (TCP port 520 for streaming)
 TELNET (RS232 over IP)
In addition NETNodes also include a number of Domo/Cobham proprietary protocols for
control and network discovery. These tend to be UDP over specific port numbers.
2.6 Multicast Packet Processing
IP multicast is a technique for one-to-many communication over an IP infrastructure in a
network. It is often used for streaming of services such as audio and video. These can take
up large bandwidths in a network. In order to manage this in the MESH system, each
NETNode functions as a multicast router allowing the flow of packets only when required. IP
multicast is often used for communication between routers/gateways.
The Internet Group Management Protocol (IGMP) is a communications protocol used by
hosts and adjacent routers on IP networks to establish multicast group memberships. In
order to perform multicast routing each NETNode acts an IGMP snooper/router.
NETNodes from v4.1 onwards support IGMP (v2) protocol. Separate multicast routing tables
are maintained for the main LAN and for each VLAN in the system.
Detailed Multicast Forwarding rules for NETNodes 2.6.1
To send multicast packets across the MESH a set of rules are applied: