Suggest an editImprove this articleRefine the answer for “What is a broadcast address?”. Your changes go to moderation before they’re published.Approval requiredContentWhat you’re changing🇺🇸EN🇺🇦UAPreviewTitle (EN)Short answer (EN)**A broadcast address** is a special IPv4 address used to send packets to all devices within one subnet at the same time. **Key point:** it is formed by setting all bits of the host part to 1, and it is not routed between networks.Shown above the full answer for quick recall.Answer (EN)Image**A broadcast address** is a special IPv4 address used to send packets **to all devices within one subnet at the same time**. Short wording for an interview: > **A broadcast address is a subnet address in which all bits of the host part are set to 1. It is used to deliver a packet to all nodes of the subnet.** --- ## Why a broadcast address is needed Broadcast is used for: - discovering devices on the network (ARP requests) - automatic configuration (DHCP Discover) - layer 2 and layer 3 service protocols - notifications within a LAN It allows you to **reach all hosts with a single packet** without needing to know their addresses. --- ## How the broadcast address is calculated Formula: > **Broadcast = all bits of the host part = 1** Example: #### Network **192.168.1.0 /24** - Mask: 255.255.255.0 - Host part = last octet All bits of the host part set to 1 → **255**: ``` Broadcast = 192.168.1.255 ``` --- #### Example with a non-standard mask: Network **10.10.5.0 /26** - Mask: 255.255.255.192 - Network range: 10.10.5.0 - 10.10.5.63 Broadcast = **10.10.5.63** --- #### Another example: Network **172.16.4.128 /25** - Host part: 7 bits - Broadcast = 172.16.4.255 --- ## Signs of a broadcast packet - Destination MAC address: `FF:FF:FF:FF:FF:FF` - Destination IP address: subnet broadcast, for example `192.168.0.255` - Received by **all** devices in the subnet - Not routed → **routers do not pass broadcast between networks** --- ## Types of broadcast transmissions #### **1. Local broadcast** Address: ``` 255.255.255.255 ``` The packet is delivered to all devices in the *current* network. Used by DHCP. --- #### **2. Directed broadcast** This is the broadcast of a specific subnet, for example: ``` 192.168.10.255 10.0.0.31 ``` It is often blocked by default on routers (due to DDoS threats). --- ## Examples of protocols that use broadcast - **ARP**: who owns this IP? - **DHCP Discover**: looks for a DHCP server - **NetBIOS** (in older Windows networks) - Some device discovery services --- ## Why broadcast is not routed Routers cut off broadcast to: - protect other networks from "storms" - avoid overloading channels - limit the broadcast domain For cross-network discovery, **multicast** or a **universal service discovery** is used. --- ## Ready answer for an interview > **A broadcast address is a special IPv4 address at which a sent packet is received by all devices within one subnet.** > **It is formed by setting all bits of the host part to 1.** > **Broadcast is used in service protocols (ARP, DHCP), but it is not routed between networks. Example: for the 192.168.1.0/24 network, the broadcast address is 192.168.1.255.** --- ## Cheat sheet (5 seconds) - Broadcast = **all bits of the host part = 1** - Example: /24 → `x.x.x.255` - Used by ARP, DHCP - Does not pass through routers - Local broadcast: `255.255.255.255`For the reviewerNote to the moderator (optional)Visible only to the moderator. Helps review go faster.