User's Manual

001-2019-500 Rev 0

Paragon4 – UHF, 700 & 800MHz User Manual

6.8.5.1 IP Broadcast/Multicast Overview

When an IP packet needs to reach more than one unit, the destination address can be set to either a broad-

cast address or a multicast address.

6.8.5.1.1 Broadcasts

Figure 39 - Broadcast Window Detail

There are two types of IP broadcast addresses:

Directed broadcast

A directed broadcast address is an IP address where the host portion is all ones (for instance

172.30.1.255 is the directed broadcast address for the network 172.30.1.0/24, 172.30.1.207 is the

directed broadcast address for the network 172.30.1.192/28).

Limited broadcast

The limited broadcast address is 255.255.255.255.

Note:

Routing equipment (to prevent broadcast storms) do not by default forward limited

broadcast packets (255.255.255.255). On the other hand, directed broadcast packets are

by default forwarded because these packets are routable like any other unicast packets.

6.8.5.1.1.1 Directed Broadcast

Each interface of a unit has its own IP address and netmask. From the IP address and netmask, it is easy

to calculate the broadcast address associated to the interface. For instance, if the Ethernet interface ad-

dress of a GeminiG3 radiomodem is 172.30.1.1/24 and the RF interface address is 10.0.1.2/24, then the

broadcast address of the Ethernet interface is 172.30.1.255 and the broadcast address of the RF interface

is 10.0.1.255.

The “Directed Broadcast” option buttons let the user select whether the unit must forward (or not) di-

rected broadcast packets. Upon reception of a directed broadcast packet, the unit takes the following ac-

tions:

If the directed broadcast address matches with one of the unit’s interface broadcast addresses:

Keep a copy for itself (pass to internal applications, if any).

If directed broadcast packets can be forwarded (Directed Broadcast is enabled):

Forwards the packet according to the routing table.

If directed broadcast packets cannot be forwarded (Directed Broadcast is disabled):

Silently discards the packet.

Note:

Occasionally, the unit cannot determine that the packet is actually a directed broadcast. In such a

case, the packet is normally routed.