Broadcast domain
Encyclopedia
A broadcast domain is a logical division of a computer network
, in which all node
s 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 inter-connected 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.
and similar systems use a shared transmission system
. In simple Ethernet (without switches or bridges), data frame
s are transmitted to all other nodes on a network. Each receiving node checks the destination address of each frame, and simply ignores any frame not addressed to its own MAC.
Switches act as buffers, receiving and analyzing the frames from each connected network segment. Frames destined for nodes connected to the originating segment are not forwarded by the switch. Frames destined for a specific node on a different segment are sent only to that segment. Only broadcast frames are forwarded to all other segments. This reduces unnecessary traffic and collisions.
In such a switched network, transmitted frames may not be received by all other reachable nodes. Nominally, only broadcast frames will be received by all other nodes. Collisions are localized to the network segment they occur on. Thus, the broadcast domain is the entire inter-connected layer two network
, and the segments connected to each switch/bridge port are each a collision domain.
Not all network systems or media feature broadcast/collision domains. For example, PPP links
". Another implementation is possible with Linux
and ebtables. One helpful analogy is that by creating multiple VLANs, the number of broadcast domains increases, but the size of each broadcast domain size 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.
Computer network
A computer network, often simply referred to as a network, is a collection of hardware components and computers interconnected by communication channels that allow sharing of resources and information....
, in which all node
Node (networking)
In communication networks, a node is a connection point, either a redistribution point or a communication endpoint . The definition of a node depends on the network and protocol layer referred to...
s can reach each other by broadcast at the data link layer
Data link layer
The data link layer is layer 2 of the seven-layer OSI model of computer networking. It corresponds to, or is part of the link layer of the TCP/IP reference model....
. 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
Ethernet
Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....
repeater
Repeater
A repeater is an electronic device that receives asignal and retransmits it at a higher level and/or higher power, or onto the other side of an obstruction, so that the signal can cover longer distances.-Description:...
or switch
Network switch
A network switch or switching hub is a computer networking device that connects network segments.The term commonly refers to a multi-port network bridge that processes and routes data at the data link layer of the OSI model...
is a member of the same broadcast domain. Further, any computer connected to the same set of inter-connected switches/repeaters is a member of the same broadcast domain. Routers and other higher-layer
Network layer
The network layer is layer 3 of the seven-layer OSI model of computer networking.The network layer is responsible for packet forwarding including routing through intermediate routers, whereas the data link layer is responsible for media access control, flow control and error checking.The network...
devices form boundaries between broadcast domains.
This is as compared to a collision domain
Collision domain
A collision domain is a section of a network where data packets can collide with one another when being sent on a shared medium or through repeaters, in particular, when using early versions of Ethernet. A network collision occurs when more than one device attempts to send a packet on a network...
, 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
Data link layer
The data link layer is layer 2 of the seven-layer OSI model of computer networking. It corresponds to, or is part of the link layer of the TCP/IP reference model....
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.
Further explanation
The distinction between broadcast and collision domains comes about because simple EthernetEthernet
Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....
and similar systems use a shared transmission system
Transmission system
In telecommunications a transmission system is a system that transmits a signal from one place to another. The signal can be an electrical, optical or radio signal....
. In simple Ethernet (without switches or bridges), data frame
Data frame
In computer networking and telecommunication, a frame is a digital data transmission unit or data packet that includes frame synchronization, i.e. a sequence of bits or symbols making it possible for the receiver to detect the beginning and end of the packet in the stream of symbols or bits...
s are transmitted to all other nodes on a network. Each receiving node checks the destination address of each frame, and simply ignores any frame not addressed to its own MAC.
Switches act as buffers, receiving and analyzing the frames from each connected network segment. Frames destined for nodes connected to the originating segment are not forwarded by the switch. Frames destined for a specific node on a different segment are sent only to that segment. Only broadcast frames are forwarded to all other segments. This reduces unnecessary traffic and collisions.
In such a switched network, transmitted frames may not be received by all other reachable nodes. Nominally, only broadcast frames will be received by all other nodes. Collisions are localized to the network segment they occur on. Thus, the broadcast domain is the entire inter-connected layer two network
Data link layer
The data link layer is layer 2 of the seven-layer OSI model of computer networking. It corresponds to, or is part of the link layer of the TCP/IP reference model....
, and the segments connected to each switch/bridge port are each a collision domain.
Not all network systems or media feature broadcast/collision domains. For example, PPP links
Point-to-Point Protocol
In networking, the Point-to-Point Protocol is a data link protocol commonly used in establishing a direct connection between two networking nodes...
Broadcast domain control
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 VLANPrivate VLAN
A private VLAN is a technique in computer networking where a VLAN contains switch ports that are restricted, such that they can only communicate with a given "uplink". The restricted ports are called "private ports". Each private VLAN typically contains many private ports, and a single uplink...
". Another implementation is possible with Linux
Linux
Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
and ebtables. One helpful analogy is that by creating multiple VLANs, the number of broadcast domains increases, but the size of each broadcast domain size decreases. This is because a virtual LAN
Virtual LAN
A virtual local area network, virtual LAN or VLAN, is a group of hosts with a common set of requirements that communicate as if they were attached to the same broadcast domain, regardless of their physical location...
(or VLAN) is technically a broadcast domain.
This is achieved by designating one or more "server
Server (computing)
In the context of client-server architecture, a server is a computer program running to serve the requests of other programs, the "clients". Thus, the "server" performs some computational task on behalf of "clients"...
" 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
Peer-to-peer
Peer-to-peer computing or networking is a distributed application architecture that partitions tasks or workloads among peers. Peers are equally privileged, equipotent participants in the application...
" traffic) is blocked.
The result is a network based on a nominally shared transmission system, like Ethernet, but in which "client
Client (computing)
A client is an application or system that accesses a service made available by a server. The server is often on another computer system, in which case the client accesses the service by way of a network....
" nodes cannot communicate with each other, only with the server/provider. A common application is Internet providers
Internet service provider
An Internet service provider is a company that provides access to the Internet. Access ISPs directly connect customers to the Internet using copper wires, wireless or fiber-optic connections. Hosting ISPs lease server space for smaller businesses and host other people servers...
. Allowing direct data link layer communication between customer nodes exposes the network to various security attacks, such as ARP spoofing
ARP spoofing
ARP spoofing, also known as ARP cache poisoning or ARP poison routing , is a technique used to attack a local-area network . ARP spoofing may allow an attacker to intercept data frames on a LAN, modify the traffic, or stop the traffic altogether...
. Controlling the broadcast domain in this fashion provides many of the advantages of a point-to-point network, using commodity broadcast-based hardware.