12 May 2020 What is broadcast domain?

A broadcast domain is a logical division of a computer network, in which all nodes can reach each other by broadcast at the data link layer. A broadcast domain can be within the same LAN segment or it can be bridged to other LAN segments. In terms of current popular technologies, any computer connected to the same Ethernet repeater or switch is a member of the same broadcast domain. Further, any computer connected to the same set of interconnected switches/repeaters is a member of the same broadcast domain. Routers and other higher-layer devices form boundaries between broadcast domains.

This is as compared to a collision domain, which would be all nodes on the same set of inter-connected repeaters, divided by switches and learning bridges. Collision domains are generally smaller than, and contained within, broadcast domains. While some layer two network devices are able to divide the collision domains, broadcast domains are only divided by layer 3 network devices such as routers or layer 3 switches. Separating VLANs divides broadcast domains as well.

A broadcast domain is a domain in which a broadcast is forwarded. A broadcast domain contains all devices that can reach each other at the data link layer (OSI layer 2) by using broadcast. All ports on a hub or a switch are by default in the same broadcast domain. All ports on a router are in the different broadcast domains and routers don’t forward broadcasts from one broadcast domain to another.

With a sufficiently sophisticated switch, it is possible to create a network in which the normal notion of a broadcast domain is strictly controlled. One implementation of this concept is termed a "private VLAN". Another implementation is possible with Linux. One helpful analogy is that by creating multiple VLANs, the number of broadcast domains increases, but the size of each broadcast domain decreases. This is because a virtual LAN (or VLAN) is technically a broadcast domain.

This is achieved by designating one or more "server" or "provider" nodes, either by MAC address or switch port. Broadcast frames are allowed to originate from these sources and are sent to all other nodes. Broadcast frames from all other sources are directed only to the server/provider nodes. Traffic from other sources not destined to the server/provider nodes ("peer-to-peer" traffic) is blocked.

The result is a network based on a nominally shared transmission system; like Ethernet, but in which "client" nodes cannot communicate with each other, only with the server/provider. A common application is Internet providers. Allowing direct data link layer communication between customer nodes exposes the network to various security attacks, such as ARP spoofing. Controlling the broadcast domain in this fashion provides many of the advantages of a point-to-point network, using commodity broadcast-based hardware.

In computer networking, telecommunication, and information theory, broadcasting is a method of transferring a message to all recipients simultaneously. Broadcasting can be performed as a high-level operation in a program, for example, broadcasting in Message Passing Interface, or it may be a low-level networking operation, for example broadcasting on Ethernet.

All-to-all communication is a computer communication method in which each sender transmits messages to all receivers within a group. In networking, this can be accomplished using broadcast or multicast. This is in contrast with the point-to-point method in which each sender communicates with one receiver.

In telecommunications, point-to-multipoint communication (P2MP, PTMP, or PMP) is communication that is accomplished via a distinct type of one-to-many connection, providing multiple paths from a single location to multiple locations. Point-to-multipoint telecommunications is typically used in wireless Internet and IP telephony via gigahertz radio frequencies. P2MP systems have been designed with and without a return channel from the multiple receivers. A central antenna or antenna array broadcasts to several receiving antennas and the system uses a form of time-division multiplexing to allow for the return channel traffic.