Suggest an editImprove this articleRefine the answer for “What is a subnet?”. Your changes go to moderation before they’re published.Approval requiredContentWhat you’re changing🇺🇸EN🇺🇦UAPreviewTitle (EN)Short answer (EN)**A subnet** is a logically distinct part of an IP network, created by dividing one network into several smaller ones. **Key point:** all devices within a subnet are in the same broadcast domain and can communicate directly.Shown above the full answer for quick recall.Answer (EN)Image**A subnet** is a logically distinct part of an IP network, created by dividing one network into several smaller ones. Short wording for an interview: > **A subnet is a group of IP addresses united by one network part, defined by the subnet mask. All devices within a subnet can communicate with each other directly and are in the same broadcast domain.** --- ## The basic idea of subnets A subnet consists of: - **a network address** - **a range of usable hosts** - **a broadcast address** - **a subnet mask (/xx)** The boundary between the *network* and *host* parts is determined by the **subnet mask**. --- ## A simple example Subnet: ``` 192.168.1.0/24 ``` - Network: **192.168.1.0** - Broadcast: **192.168.1.255** - Host range: **192.168.1.1 - 192.168.1.254** - Number of hosts: 254 All these addresses are: **one subnet**. --- ## What using subnets gives you ### **1. Dividing the network into smaller segments** Allows splitting a large network into: - departments (IT, accounting, HR) - VLANs - different branches - server segments This reduces load and makes the network more structured. --- ### **2. Limiting broadcast domains** Broadcast (ARP, DHCP) operates within a subnet. If a subnet is too large → a lot of broadcast traffic → load. Subnets help **isolate traffic**, improving performance. --- ### **3. Increasing security** Different subnets can be filtered at the level of: - ACLs - a firewall - a router For example: - servers in the 10.0.10.0/24 subnet - users: 10.0.20.0/24 - access policies are applied between them --- ### **4. Efficient routing** Routers use the network part of the IP to determine where to send a packet. Subnets: - reduce the routing table - are convenient for aggregation (summarization) --- ## Subnet calculation formula Number of hosts: ``` 2^(number of zeros in the mask) - 2 ``` Examples: | Mask | Hosts | Where it is used | |---|---|---| | /24 | 254 | Home/office networks | | /25 | 126 | Splitting /24 in half | | /26 | 62 | Small departments | | /30 | 2 | Point-to-point links | --- ## Example of dividing a network (subnetting) We have the network: ``` 192.168.1.0/24 ``` We want 4 subnets. /24 → split into /26: Subnets: ``` 192.168.1.0/26 192.168.1.64/26 192.168.1.128/26 192.168.1.192/26 ``` Each subnet contains **64 addresses, 62 hosts**. --- ## Subnet = broadcast domain All devices in one subnet: - are in the same broadcast domain - can communicate directly (without a router) - use ARP to find each other To cross subnet boundaries, a **router or VLAN routing** is required. --- ## Ready answer for an interview > **A subnet is a logically distinct part of an IP network, defined by the subnet mask.** > **It sets the address range, broadcast behavior, and the boundaries of the broadcast domain.** > **All hosts within a subnet can communicate directly, while a router is required to connect different subnets.** > **Subnets are used for network segmentation, security, and routing optimization.** --- ## Cheat sheet (5 seconds) - Subnet = part of a network, defined by the **mask**. - Contains: **network**, **hosts**, **broadcast**. - All hosts → one broadcast domain. - A router is needed to connect subnets. - Used for segmentation, security, and optimization.For the reviewerNote to the moderator (optional)Visible only to the moderator. Helps review go faster.