1. What Are Network Communication Types?

Network communication methods describe how traffic is delivered from a sender or source to one or more destinations.

The four terms are:

• Unicast: One sender communicates with one destination.
• Broadcast: One sender sends traffic to all devices within a local broadcast domain.
• Multicast: One sender sends traffic to a group of interested receivers.
• Anycast: Multiple devices or locations advertise the same destination address, and routing directs traffic to one selected destination, usually according to routing metrics and policy.

These models solve different problems. Broadcast is a local delivery mechanism, multicast is group-oriented delivery, and anycast uses routing to direct traffic toward one of several possible destinations.

2. What Is Unicast?

Unicast is one-to-one communication. A sender transmits data to a specific destination host or network endpoint.

Example

When you open a website, your device commonly establishes a connection with a web server using unicast communication.

       [Computer A]
             |
             | Unicast traffic
             v
       [Router / Network]
             |
             v
        [Server B]

      One sender → One destination
        

Characteristics of Unicast

• Targets a specific destination.
• Commonly used for web browsing, email, file transfers, and SSH connections.
• Each receiver typically receives its own unicast stream or connection.
• Works across routed networks when appropriate reachability exists.

Example IP addresses: 192.168.1.10 and 192.168.1.20 can be individual IPv4 host addresses on a private LAN, depending on the subnet configuration.

3. What Is Broadcast?

Broadcast is one-to-all communication within a broadcast domain. In IPv4 Ethernet networks, a broadcast frame is addressed to all devices on the relevant Layer 2 broadcast domain.

Example: ARP Request

When an IPv4 device needs to discover the MAC address associated with an IPv4 address on its local subnet, it may send an ARP request as an Ethernet broadcast.

               [PC A]
                  |
             Broadcast
                  |
             [Switch]
             /   |   \
          [PC B][PC C][PC D]

       All devices in the broadcast domain
       receive the broadcast frame.
        

Characteristics of Broadcast

• Reaches devices in the relevant broadcast domain.
• Can be useful for local discovery and specific network protocols.
• Can create unnecessary traffic when used excessively.
• Routers normally do not forward ordinary IPv4 broadcast traffic between subnets.

Example: For a subnet of 192.168.1.0/24, the directed IPv4 subnet broadcast address is 192.168.1.255. The all-ones limited broadcast address is 255.255.255.255.

IPv6 does not use broadcast addresses. It uses multicast for many functions that require communication with groups of neighboring devices.

4. What Is Multicast?

Multicast is one-to-many communication with a selected group of receivers. The sender sends traffic to a multicast group, and the network delivers it to interested receivers when multicast is supported and configured.

Example

A live video stream may be distributed to multiple students who have joined the same multicast group on a multicast-enabled network.

           [Video Server]
                  |
             [Multicast Router]
              /      |      \
             /       |       \
          [PC A]   [PC B]   [PC C]
           Join     Join    Not joined

       Traffic is delivered according to
       multicast group membership and routing.
        

Characteristics of Multicast

• Targets a group rather than every device.
• Can reduce duplicate traffic on shared network paths.
• Used in supported IPTV, live-streaming, and data-distribution systems.
• IPv4 multicast uses 224.0.0.0/4; IPv6 multicast uses FF00::/8.
• IPv4 group membership is commonly managed with IGMP, while multicast routing may use PIM.

5. What Is Anycast?

Anycast is a delivery model in which multiple network destinations advertise the same IP address or prefix, and routing directs a client toward one selected destination.

The destination is selected by routing and network policy. It is often a topologically preferred or nearby location, but it is not necessarily the geographically closest server.

Example: DNS Services

A DNS provider can operate servers at several locations that advertise the same service IP address. Depending on routing, a client may reach one of those locations without needing to know which physical server was selected.

             [User in Sri Lanka]
                      |
                      |
                 [Routing]
                 /       \
                /         \
       [DNS Location A]  [DNS Location B]
          Same IP prefix advertised

       Routing selects one reachable path
       toward one destination location.
        

Characteristics of Anycast

• Multiple destinations advertise the same IP address or prefix.
• Routing selects a path toward one of those destinations.
• Can improve service resilience and distribute traffic across locations.
• Commonly used by DNS services, content delivery networks, and some distributed network services.
• Requires careful routing, health monitoring, and service design.

Important: Anycast is not the same as sending one packet to every server. A given packet is normally routed toward one selected destination along the chosen path.

6. Unicast vs Broadcast vs Multicast vs Anycast: Comparison Table

7. Simple Way to Remember All Four

UNICAST
One sender --------------> One receiver

BROADCAST
One sender --------------> All devices
                             in the local
                         broadcast domain

MULTICAST
One sender --------------> Selected group
                             of receivers

ANYCAST
One sender --------------> One selected
                         destination from
                         multiple locations
        

Think of a classroom:

• Unicast: You send a message to one student.
• Broadcast: You announce a message to everyone in the classroom.
• Multicast: You send a message to a selected study group.
• Anycast: You contact a service available at multiple locations, and the network routes your request to one selected location.

8. How Do These Models Relate to IP Addresses?

Unicast Addresses

Identify individual interfaces or destinations for one-to-one communication. For example, 192.168.1.10 may be a private IPv4 host address.

Broadcast Addresses

IPv4 uses broadcast addressing for delivery to all devices in a broadcast domain. For example, 192.168.1.255 is the directed broadcast address for 192.168.1.0/24.

Multicast Addresses

IPv4 multicast uses the 224.0.0.0/4 block. IPv6 multicast addresses begin with FF00::/8.

Anycast Addresses

Anycast generally uses an address from an address range suitable for unicast. The same address or prefix is configured at multiple locations and advertised through routing. It is the routing arrangement, rather than a special standalone IPv4 address block, that provides anycast behavior.

9. When Should Each Method Be Used?

10. Common Interview Questions

11. Key Takeaways

• Unicast: One sender to one destination.
• Broadcast: One sender to all devices in the relevant broadcast domain.
• Multicast: One sender to a selected group of receivers.
• Anycast: One sender reaches one destination selected from multiple locations through routing.
• IPv4 supports broadcast; IPv6 does not use broadcast addresses.
• Multicast group delivery requires suitable receiver membership and network support.
• Anycast depends on routing configuration and does not guarantee geographic proximity.