What is DHCP (Dynamic Host Configuration Protocol) Relay?

Published on: 2024 May 10

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15 min read

A networking mechanism called the DHCP (Dynamic Host Configuration Protocol) is used to dynamically assign IP addresses to each host on a computer network. Moreover, subnet masks, default gateways, and Domain Name System (DNS) addresses are assigned using DHCP.

Any device that permits access to a network can be referred to as a host in this DHCP sense. Personal devices, thin clients, and desktop and laptop computers are a few examples. All of these devices are given IP addresses thanks to DHCP.

Default gateways, subnet masks, and Domain Name System (DNS) addresses are assigned via DHCP within the framework of this standard. Within the boundaries of a network, all of these allow devices to connect with one another and the internet.

One easy way to send DHCP messages between subnets is to use a DHCP relay. A router or switch that receives DHCP requests on one interface and passes them to another interface, where a DHCP server may be reached, is known as a DHCP relay agent. The relay agent receives a response from the DHCP server and forwards it to the client. In this manner, even if they are not on the same subnet, the client and server can exchange IP addresses.

Before implementing DHCP relay and proxy, there are a few things to keep in mind. These include higher network latency from additional hops and processing for DHCP messages, decreased network reliability from a single point of failure or bottleneck for DHCP service, more difficult network troubleshooting from obscured source and destination of DHCP messages or altered contents, and limited network flexibility from DHCP server or client-only options or features.

The kind and model of the device being used as the relay or proxy agent determines how the DHCP relay and proxy are configured. Generally speaking, you need to provide the interface or interfaces that will receive and pass the DHCP messages, the IP address or addresses of the DHCP server or servers that will give the IP addresses, and the device's DHCP relay or proxy service to be enabled. You may set up any other options or settings that you would like to apply to the DHCP messages.

In addition to all of these, this page covers a plethora of other subjects related to DHCP Relay, including:

• Why is DHCP Needed in Networking?

• Why is DHCP Configuration Important?

• How Does DHCP Relay Differ from DHCP in Terms of Functionality?

• What Role Does DHCP Relay Play in a Network with Multiple Subnets?

• What are the Key Components Involved in DHCP Relay Configuration?

  1. DHCP Relay Agent
  2. Interfaces
  3. IP Helper Address
  4. Subnet Configuration
  5. DHCP Server
  6. DHCP Messages
  7. Network Topology
  8. Routing Configuration
  9. Security Settings
  10. Verification and Testing Tools
  11. Logging and Monitoring

• How Does a Router or Layer 3 Switch Act as a DHCP Relay Agent?

• How to Configure DHCP Relay on a Router or Layer 3 Switch?

• Are There Specific Considerations or Settings When Configuring DHCP Relay for IPv6 Networks?

• What are the Security Implications of DHCP Relay?

• Can DHCP Relay Operate in Environments with Multiple DHCP Servers?

• How Does DHCP Relay Impact Network Performance or Latency?

• How Does DHCP Relay Contribute to Efficient IP Address Management in Large Networks?

• How Does DHCP Relay Interact with VLANs?

Why is DHCP Needed in Networking?

For a device to access the network and its resources on a TCP/IP-based network, it needs a distinct unicast IP address.Without DHCP, IP addresses must be manually assigned to new devices or machines migrating within a subnet, and IP addresses that have been destroyed by the network must be manually retrieved.

This entire process is automated and managed centrally via DHCP. When a DHCP-enabled client joins the network, the DHCP server allocates an IP address from a pool that it maintains. Because IP addresses are leased dynamically rather than statically, they are immediately returned to the pool for reallocation once they are no longer in use. In order to preserve TCP/IP configuration data and deliver address configuration to DHCP-enabled clients in the form of a lease offer, the network administrator sets up DHCP servers. The configuration data is kept by the DHCP server in a database that contains the following details:

• Enough TCP/IP setup options for every network client.
• IP addresses that are excluded and valid that are kept in a pool for client assignment.
• Reserved IP addresses connected to certain DHCP users. This makes it possible to consistently assign one IP address to one DHCP client.
• The term of the lease, or the amount of time that can pass before an IP address needs to be renewed,.

When a DHCP-capable client accepts a lease offer, they get an IP address that is active and connected to the subnet in question. Requested DHCP options are extra settings that clients are set to receive from a DHCP server. The router (default gateway), DNS servers, and DNS domain name are a few instances of DHCP settings.

Why is DHCP Configuration Important?

All devices functioning in a Transmission Control Protocol/Internet Protocol network require an IP address, which is an essential component. This procedure is simplified and made less laborious by a set of rules called DHCP.

Devices need to have IP addresses assigned to them, whether or not DHCP is in place. This is because device IP addresses have the data necessary to precisely guide the transport of packets over networks. In the absence of DHCP, machines that are relocated to a different network will need to manually configure themselves in order to receive new IP addresses. Likewise, it is necessary to manually retrieve the IP addresses given to machines that have disconnected from the network. On the other hand, DHCP handles everything automatically. Any client that is on its radar can lease an IP address from the pool of available addresses that the DHCP server maintains. When a client uses DHCP, the addresses are leased; they are not permanently linked to that device, but rather assigned to it for a brief period of time. Because the leased address is dynamic, any devices that are not in use are promptly returned to the pool and can be assigned to another device.

By assigning an IP address to several computers simultaneously, DHCP reduces address conflicts and typographical mistakes that might occur when configuring IP addresses manually.

The following functions of DHCP are included to lessen network administration:

• TCP/IP setting that is automated and centralized.
• The capability of centrally defining TCP/IP setups.
• The use of DHCP options to allocate a whole range of extra TCP/IP configuration settings.
• The effective management of IP address changes for clients that need to be updated often, such mobile devices on a wireless network that roam around.

A DHCP server is not required on any subnet thanks to the delivery of initial DHCP messages via a DHCP relay agent.

How Does DHCP Relay Differ from DHCP in Terms of Functionality?

A DHCP server may automatically provide an IP address to each DHCP client when necessary, thanks to the Dynamic Host Configuration Protocol (DHCP). In order to locate the DHCP server, a client connects to a network and sends an IP broadcast packet that is only viewable inside the subnet that the requester is on. DHCP servers are usually not distributed across all subnets; instead, they are centralized.

When there are no DHCP servers accessible on their local subnet, DHCP clients can still connect with one another using DHCP Relay. Discover messages are routed to a configured DHCP server by a relay agent using IP routing. The DHCP offer is then returned to the client network by the relay agent.

What Role Does DHCP Relay Play in a Network with Multiple Subnets?

An essential component of network communication are DHCP relay agents. They make it possible for devices to join a network even if they are not in the same broadcast domain or subnet.

They assist in making sure that devices receive the right IP address and other configuration data required for network communication by transmitting DHCP signals between clients and servers. Organizations may effortlessly manage their networks with their assistance, free from the fear of IP address conflicts or other issues brought on by improper configuration settings.

Requests between DHCP clients and servers are handled by the DHCP relay. Relays are typically employed when a company manages sizable or intricate networks.

The subnet, lease, IP address pool, and DHCP communications protocol are further elements.

The broadcasted DHCP discovery is received by the DHCP relay, which then transforms it into a unicast packet meant for the DHCP server.

What are the Key Components Involved in DHCP Relay Configuration?

Devices that join your network get signals from DHCP protocols that provide them with the information they need to interact with basic network activities. Consider a scenario in which your phone, tablet, and laptop could all connect to a tiny home network. Given that there are just three devices, it might not be too tough to issue an IP address to each of them. However, if you had to issue IP addresses, subnet masks, DNS addresses, and other necessary information for a few hundred devices, it would be significantly more laborious and time-consuming. This information is immediately sent to all connected devices using DHCP.

Any TCP/IP host that is used to transfer requests and answers between the client and DHCP server when the server is located on a separate network is known as a DHCP relay agent. After receiving DHCP messages, relay agents create a fresh message to be sent across a different interface. In addition, if enabled, the DHCP relay agent adds the relay agent information option 82 and the giaddr (gateway address of the packet) field. When the host receives the server reply, the options field is deleted.

In big business networks, when the DHCP server is situated on a separate network segment from the client devices, DHCP relay agents are frequently employed. After receiving DHCP broadcast messages from client devices, the DHCP relay agent encapsulates those messages in a unicast packet and delivers them to the DHCP server. One or more DHCP server IP addresses that the DHCP relay agent can route requests to may be put into its configuration. The IP address of the relay agent interface on which the message was received is shown in the giaddr field of the DHCP relay agent message. You can add more information to the DHCP request message (such as the VLAN ID of the requesting device or the interface or port number on which the request was received) by using the Relay Agent Information option (option 82). DHCP relay agents can be installed as software on routers or other network devices, or they can be deployed as dedicated hardware. Additional functionality like DHCP packet filtering, rate limitation, or access restriction based on the source or destination IP address may be included in some DHCP relay agents. Inadequate configuration of a DHCP relay agent can result in DHCP process delays or failures, which affect client devices' ability to connect to the network.

There are several parts that make up DHCP, including the relay, client, and server. The main components of DHCP Relay can be enumerated as follows:

DHCP Component	Description
1. DHCP Relay Agent	Requests between DHCP clients and servers are handled by the DHCP relay. Relays are typically employed when a company manages sizable or intricate networks.
2. DHCP Client	Any IP device connected to the network and set up to function as a host, seeking setup settings from a DHCP server, such as an IP address, is known as a DHCP client.
3. IP Helper Address	The set of addresses that are accessible to DHCP clients is known as the IP address pool. Usually, IP addresses are distributed in descending order of value.
4. Subnet Configuration	Subnets are smaller IP network segments that are divided to maintain network management. These are connections inside a larger network.
5. DHCP Server	The networked device that runs the DHCP service is called the DHCP server, which is usually either a server or a router. IP addresses and associated configuration data are stored on the DHCP server.
6. DHCP Messages	Eight common message types are used by DHCP, and they are recognized by an option type number in the message.
7. Network Topology	A number of things need to be taken into account when designing your Dynamic Host Configuration Protocol (DHCP) configuration, including your network topology, network devices (such as routers), and the way you wish to support your customers using DHCP.
8. Routing Configuration	DHCP messages can be relayed by the firewall or router. You must enable DHCP relay on the firewall or router interface where the DHCP requests are coming from (the client's network) if DHCP messages are routed through the firewall (from one isolated network segment to another).
9. DHCP Leases	It is only the period of validity for the data obtained from the server; if the lease expires, the tenant will need to reassign it.
10. Documentation and Testing Tools	A program that assists you in keeping track of your DHCP setup and use is known as a DHCP documentation tool. Software that assists you in confirming the security and operation of your DHCP server and clients is known as a DHCP testing tool.
11. Logging and Monitoring	Administrators may see which devices are utilizing which IP addresses and when leases are given or renewed by using the audit logs that DHCP servers can save of all DHCP operations.

Table 1. DHCP Components

1. DHCP Relay Agent

Any TCP/IP host acting as a DHCP relay agent is one that transfers DHCP messages between servers and clients when a DHCP server and a DHCP client are located in separate subnets. For instance, with the aid of DHCP relay agents found on the connecting routers, a single DHCP server may service every client in a sizable network with several subnets.

2. DHCP Client

Any IP device connected to the network and set up to function as a host, seeking setup settings from a DHCP server, such as an IP address, is known as a DHCP client. An external DHCP server provides the IP address and TCP/IP parameters for every device operating as a DHCP client.

3. IP Helper Address

IP helper address defines the address of a remote DHCP server or DHCP relay agent.

4. Subnet Configuration

Subnets are smaller IP network segments that are divided to maintain network management. These are connections inside a larger network. Each network that your DHCP server serves needs a subnet declaration. Numerous subnet declarations are needed for numerous subnets. The DHCP server does not serve a network if it does not have a network interface within the range of a subnet declaration.

The range of IP addresses and subnets that the server can give to clients, as well as the lease term for each address and subnet, must be specified when configuring a DHCP server.

5. DHCP Server

The device that connects to your network is automatically assigned an IP address and other network information by the system using a DHCP server. It can supply dynamic or transitory IP addresses that are drawn from a pool of accessible addresses.

Furthermore, permanent IP addresses and DHCP setup parameters—such as subnet masks, default gateways, and DNS servers—are provided by DHCP servers.

The client device is assigned the following configuration settings by the DHCP server:

• gives all clients on a certain subnet temporary IP addresses from an IP address pool (dynamic binding)
• depending on the media access control (MAC) addresses of particular clients assigns persistent IP addresses to such clients (static binding).

6. DHCP Messages

Eight common message types are used by DHCP, and they are recognized by an option type number in the message. For instance, a client sends a DHCPDISCOVER message on its local physical subnetwork when it wishes to locate a DHCP server. The message is sent to DHCP servers on a separate physical subnet if there isn't a DHCP server on its subnet and DHCP Helper or DHCP Relay is set up correctly. If not, the message will only reach the subnet from which it came. A DHCPOFFER message containing an available network address and additional setup details will be returned by one or more DHCP servers.

The client sends a DHCPREQUEST to one or more servers when it wants an IP address. RFC 2131 stipulates that the broadcast message sent by the client must have a source address of 0 in its IP header since the client is seeking an IP address, it doesn't yet have one.

The DHCP messages are included in the table below.

• A DHCP Discovery: To locate accessible DHCP servers, use client broadcast.

• DHCPOFFER: In response to a client's DHCPDISCOVER request, the server provides configuration parameters.

• DHCPREQUEST: The client sends a message to one or more servers requesting the following actions:

  • One server may give parameters, while other servers may tacitly reject proposals.
  • Verify the accuracy of an address that was previously assigned, maybe following a system reboot.
  • Extend a network address's lease.

• DHCPACK: Acknowledgment message from the server to the client that includes configuration information, such as a verified network address.

• DHCPNAK: A negative acknowledgment from the server to the client indicates that either the client's lease has ended or the client believes the network address is wrong (for instance, if the client has relocated to a new subnet).

• DHCPDECLINE: Communication from the client to the server saying that the network address is already in use.

• DHCPDISCLOSURE: Sending a message from the client to the server, the user surrenders the network address and the remaining lease period is canceled.

• DHCPINFORM: The client has an externally defined network address; the server is receiving a message from the client seeking only local configuration details.

7. Network Topology

A number of things need to be taken into account when designing your Dynamic Host Configuration Protocol (DHCP) configuration, including your network topology, network devices (such as routers), and the way you wish to support your customers using DHCP.

A key component of DHCP deployment planning is comprehending the topology or network configuration. Knowing your network architecture can help you rapidly determine which IP address ranges are available for DHCP, what configuration details each client needs, which devices need to be set up to forward DHCP messages, and whether DHCP can be used with your DNS or PPP servers. You could even wish to draw your network architecture on a piece of scrap paper, depending on how complicated your network is. All LANs, the devices that link the LANs, and the IP addresses of clients and equipment (such as printers) that require a specified IP address must be included. Consider examining a few of the DHCP situations to assist you in designing your network topology.

8. Routing Configuration

DHCP messages can be relayed by the firewall or router. You must enable DHCP relay on the firewall or router interface where the DHCP requests are coming from (the client's network) if DHCP messages are routed through the firewall (from one isolated network segment to another). DHCP relay supports addresses that are both IPv4 and IPv6. On the same firewall interface, IPv4 and IPv6 DHCP relays can be enabled.

9. DHCP Leases

The IP address block is under the DHCP server's authority. It permits the lease-based usage of IP addresses by DHCP clients. The customer "leased" the IP address for a certain period of time. The lease time is determined by the administrator and can range from 120 seconds to infinity. DHCP ensures that the IP address allocated to a client won't be transferred to another client for the duration of the lease.

The DHCP client automatically seeks an extension of its lease before the expiration date. The DHCP server will extend the lease as long as the client is able to reach it. For instance, client A tries to extend its lease before shutting off when it reboots. Client A may be given a different IP address if it is turned off at the end of the renewal period. When client A reconnects to the network, the server may assign client A the same IP address if it is still available. However, client A will receive a different IP address if the server sends the IP address to client B while client A is offline.

10. Documentation and Testing Tools

Software that assists you in confirming the security and operation of your DHCP server and clients is known as a DHCP testing tool. You may use it to check vulnerabilities, create traffic, and simulate scenarios. To test your DHCP server's ability to handle various request types, reply to malicious or invalid packets, resolve conflicts or failures, and enforce regulations or rules, for instance, you can use a DHCP testing tool. Nmap, DHCP Test Client, and DHCP Explorer are a few DHCP testing tools.

A program that assists you in keeping track of your DHCP setup and use is known as a DHCP documentation tool. You may use it to record your leases, scopes, options, reservations, exclusions, logs, and DHCP settings. Additionally, it may assist you in creating reports, charts, or diagrams that will make your DHCP data easier to see and comprehend. To view the configuration of your DHCP server, IP address space allocation, DHCP option application, and DHCP event logging, for instance, utilize a DHCP documentation tool. Infoblox IPAM, NetBox, and Microsoft DHCP Server Callout DLL are a few examples of DHCP documentation tools.

11. Logging and Monitoring

Administrators may see which devices are utilizing which IP addresses and when leases are given or renewed by using the audit logs that DHCP servers can save of all DHCP operations.

How Does a Router or Layer 3 Switch Act as a DHCP Relay Agent?

The DHCP relay agent's job is to forward DHCP messages to other subnets, allowing the DHCP server to reside on a different subnet than the DHCP clients. The DHCP relay agent routes DHCP messages from DHCP clients on a network without a DHCP server to other subnets. It also sends responses from DHCP servers to DHCP clients. Routers and layer 3 switches have a DHCP relay option. The DHCP relay agent is compatible with layer 3 interfaces, layer 3 VLAN interfaces, and LAG interfaces. The DHCP relay is not supported by the administration interface. Moreover, the DHCP relay agent is VRF aware and acts as follows when VRFs are defined on the switch:

• DHCP client requests received on an interface are routed to the specified servers via the VRF that the interface is a member of.

• DHCP server replies received on an interface are routed to the client that may be reached via the VRF that the interface is a member of.

• DHCP Server Interoperation

The same VRF can be used for both DHCP relay and DHCP server configurations.

How to Configure DHCP Relay on a Router or Layer 3 Switch?

The general steps to configure the DHCP relay on a router or L3 switch are as follows:

1. Access the router or Layer 3 switch configuration interface.
2. Locate the DHCP settings and enable the DHCP relay feature. This may involve selecting a specific interface or VLAN for relaying DHCP requests.
3. Configure the IP address of the DHCP server that will be responsible for assigning IP addresses to clients.
4. Configure the IP helper address on the interface or VLAN where DHCP requests need to be relayed.

Are There Specific Considerations or Settings When Configuring DHCP Relay for IPv6 Networks?

While DHCP relay in IPv6 functions similarly to IPv4, there are specific considerations:

• Unicast vs. Multicast: IPv6 DHCP servers typically use multicast for client discovery, while IPv6 relays use unicast to forward requests and replies. This requires configuration on both the relay and server.

• VRRP Support: The relay can be a VRRP address, forwarding messages only when in the Master state. This ensures redundancy and avoids forwarding loops.

• Interface Configuration: The relay interface requires specific IPv6 settings, including enabling DHCP relay and specifying the server's address.

What are the Security Implications of DHCP Relay?

Here are the security implications of the DHCP relay.

• Rogue DHCP servers: A rogue DHCP server is an unauthorized device that provides DHCP services to network clients. A maliciously designed DHCP server might issue inaccurate or conflicting IP addresses, subnet masks, gateways, or DNS servers to network clients. This can result in network interruption, misrouting, denial of service, and man-in-the-middle attacks. To avoid rogue DHCP servers, utilize DHCP snooping, which filters DHCP communications depending on the sender's source port and MAC address. You should enable port security, which limits the number of MAC addresses permitted on a switch port.

• DHCP starvation: DHCP starvation is an attack that depletes a DHCP server's available IP address pool by delivering a high number of DHCP requests using faked MAC addresses. This may prohibit genuine network clients from gaining IP addresses and accessing the network. To avoid DHCP hunger, you should enable DHCP snooping, which restricts the number of DHCP queries per port. You should enable dynamic ARP inspection, a capability that checks ARP packets using the DHCP snooping database.

• DHCP spoofing: DHCP spoofing is an attack that intercepts and changes DHCP communications sent between a DHCP server and a network client. A DHCP spoofer can change the IP address, subnet mask, gateway, or DNS server issued to a network client. This allows the attacker to divert network traffic, launch man-in-the-middle assaults, and steal sensitive data. To prevent DHCP spoofing, employ IP source guard, a feature that checks the source IP address of packets against the DHCP snooping database. You should enable DHCP authentication, which uses digital signatures to verify the authenticity and integrity of DHCP communications.

• Unauthorized DHCP clients: An unauthorized DHCP client is a device that connects to a network without authorization and requests an IP address from a DHCP server. An illegal DHCP client might deplete network resources, create security flaws, or disrupt other network devices. To prevent unauthorized DHCP clients, you should enable MAC address filtering, which accepts or refuses DHCP requests depending on the device's MAC address. You should enable network access control, which enforces security standards and compliance on network devices.

• DHCP Relay Attacks: A DHCP relay attack is one that targets the DHCP relay agent, which is a device that forwards DHCP signals across network segments. A DHCP relay attack can circumvent the security features of the DHCP server or the network segment, including the DHCP relay agent. An attacker, for example, can use a compromised DHCP relay agent to send malicious DHCP signals or get access to restricted network segments. To avoid DHCP relay attacks, enable DHCP relay authentication, which uses digital signatures to verify the authenticity and integrity of DHCP communications. You should utilize firewall rules, which are features that restrict how traffic flows across network parts.

• DHCP scripting vulnerabilities: DHCP scripting is a way for automating and customizing DHCP processes via scripts. DHCP scripting can help manage big or complicated networks, but it can bring security flaws if the scripts are not properly designed, tested, or secured. For example, a DHCP script may have mistakes, vulnerabilities, or backdoors that might compromise the DHCP server or the network. To avoid DHCP scripting vulnerabilities, use recommended practices while creating, testing, and securing DHCP scripts. You should employ code review, which is a technique for ensuring the quality and security of DHCP scripts prior to deployment.

Can DHCP Relay Operate in Environments with Multiple DHCP Servers?

Yes, An interface can be set up with several DHCP relays. When a client sends a DHCP request, the server delivers it to all specified servers at the same time, without waiting for a response. Each server returns an IP address to the client, but the client typically uses the IP address from the first answer it gets. This allows DHCP queries to be sent to all specified servers concurrently, decreasing wait times and possible bottlenecks.

How Does DHCP Relay Impact Network Performance or Latency?

DHCP relay agents enhance network speed and minimize latency by transforming broadcast DHCP messages into unicast messages, which are then sent straight to the DHCP server. This minimizes the network congestion and enhances the effectiveness of the DHCP service. The proximity of the DHCP server to the distant client does not have a direct impact on network speed or latency, since DHCP is a relatively low-impact protocol. Nevertheless, greater distances may lead to somewhat extended DHCP response times.

How Does DHCP Relay Contribute to Efficient IP Address Management in Large Networks?

DHCP makes IP address administration easier by automating the allocation, renewal, and release of IP addresses. This eliminates the need for network managers to manually issue IP addresses to each device, track which addresses are in use, or deal with conflicts or duplicates. DHCP enables network managers to centrally monitor and update network setup settings, such as DNS servers or domain names, eliminating the need to configure each device separately. DHCP allows for dynamic network changes, such as adding or deleting devices, altering network architecture, or scaling up or down network size, without impacting IP address availability or performance.

IT pros may face difficulty managing several devices on a single network. DHCP (Dynamic Host Configuration Protocol) Relay is a useful technology for managing several devices in a single network. It enables the user to assign IP addresses to all connected devices without needing to setup each one manually. This enables customers to control their whole network from a single location and ensures that all connected devices have legitimate IP addresses.

The DHCP relay protects network resources by preventing unwanted access and avoiding device conflicts caused by multiple IP addresses. It allows users to simply add new devices to their networks since they will obtain proper IP configuration from the DHCP server. All of these qualities make DHCP Relay an indispensable tool for managing numerous devices on a single network, and it contributes to effective IP address management in large networks.

How Does DHCP Relay Interact with VLANs?

A virtualized connection, known as a virtual local area network (VLAN) unites various network nodes and devices from several local area networks (LANs) into a single logical network. In technical terms, a segment serves a specific department and is separated from the rest of the LAN by a bridge, router, or switch. This indicates that all workstations within the VLAN get packets broadcast by a workstation, but none outside of it.

VLAN is a characteristic of switches. It establishes a collection of devices inside the local network that exchange broadcast messages. A broadcast message that originates in one VLAN does not make its way to another. Clients and a DHCP server converse via broadcast messages. Therefore, DHCP clients won't ever get IP configurations if a DHCP server is configured in one VLAN and DHCP clients are configured in another VLAN. When clients and the DHCP server are accessible inside the same VLAN, DHCP functions. Every VLAN in a network that has more than one must have its own DHCP pool configured.

Switches employ VLANs to regulate and limit broadcast messages. A VLAN establishes a broadcast message's logical border. The switch only forwards broadcast messages inside the designated VLAN if one is specified. Although VLANs save broadcast message space, they present issues for programs that depend on broadcast messages. This is how they improve networks. For instance, broadcast messages are used by DHCP to facilitate communication between the DHCP server and DHCP clients.

It is not possible for clients to get IP configuration from the server if the DHCP server and clients are set up in separate VLANs. We have two choices for resolving this problem. Either set up a DHCP server for every VLAN or set up many DHCP pools on the DHCP server and enable DHCP relay for each VLAN interface. DHCP relay enables communication between DHCP clients located on separate VLANs and a centralized DHCP server. The switch's DHCP relay agent transfers DHCP requests from clients in a specific VLAN to the DHCP server and then transmits the DHCP server's replies back to the corresponding VLAN.

In order to enable DHCP relay across VLANs, it is necessary to set up a switched virtual interface (SVI) on the switch for each VLAN and include the "ip helper-address" command to specify the DHCP server. This guarantees that Dynamic Host Configuration Protocol (DHCP) requests from clients located in various Virtual Local Area Networks (VLANs) are appropriately sent to the designated DHCP server.