DHCP Protocol Explanation
Slide 1: DHCP Overview
1. Goal:
- DHCP (Dynamic Host Configuration Protocol) allows devices (hosts) to dynamically get
an IP address when they connect to a network.
- Benefits:
- Dynamic IP allocation: Assigns IPs automatically to devices joining the network.
- Lease renewal: Devices can renew their IP addresses if still in use.
- Address reuse: Frees up IP addresses once a device disconnects.
- Support for mobility: Works for mobile devices that frequently join or leave networks.
2. DHCP Process Overview:
- DHCP Discover: The device sends a broadcast message to find a DHCP server.
- DHCP Offer: The server replies with an available IP address.
- DHCP Request: The device requests the offered IP address.
- DHCP ACK: The server confirms and assigns the IP to the device.
Slide 2: DHCP Client-Server Scenario
1. Diagram Explanation:
- The network contains a DHCP server connected to several devices.
- Devices in the network need IP addresses, and the DHCP server allocates them.
- Example:
- Devices like 223.1.1.1 and 223.1.2.1 are already configured.
- New devices like 223.1.1.3 request IPs dynamically.
2. DHCP Server Placement:
- Often integrated into routers managing subnets.
- Ensures new devices arriving on a network can get an IP address immediately.
Slide 3: Detailed Client-Server Communication
1. Steps in Communication:
- Step 1: Client sends a DHCP Discover broadcast (e.g., “Is there any DHCP server?”).
- Step 2: DHCP server responds with a DHCP Offer, offering an IP address.
- Step 3: Client sends a DHCP Request message to confirm it wants the offered IP.
- Step 4: DHCP server sends an ACK (Acknowledgment) to finalize the assignment.
2. Example:
- Client requests IP 223.1.2.6. The server assigns this address and provides lease details,
DNS, and router information.
Slide 4: DHCP Provides More than IPs
1. Additional Configuration:
- DHCP can deliver extra network settings to the client:
- Router Address: The gateway for accessing external networks.
- DNS Server Address: For resolving domain names.
- Subnet Mask: To distinguish the network and host portions of the IP.
Slide 5: DHCP Example (Client Request)
1. Network Structure:
- A router has a DHCP server built-in and connects multiple devices.
2. Steps for Client to Get an IP:
- Step 1: Client sends a DHCP Request encapsulated in UDP and Ethernet frames.
- Step 2: Broadcasts are sent to all devices on the LAN.
- Step 3: Ethernet and UDP headers are stripped off when the request reaches the DHCP
server.
Slide 6: DHCP Example (Server Reply)
1. How the Server Responds:
- DHCP server sends a DHCP ACK, confirming the IP address, router, and DNS server
details.
- The reply is encapsulated in the same layers (UDP/IP/Ethernet) for delivery.
2. Client Configuration:
- The client saves the provided IP address, router info, and DNS settings for use.
Slide 7: IP Addresses: How to Obtain One
1. How Networks Get IPs:
- Networks receive a block of IP addresses from their ISP (Internet Service Provider).
- Example: ISP assigns a block (e.g., 200.23.16.0/20).
- The /20 indicates the network size.
2. Subnet Allocation:
- The ISP can divide its block into smaller subnets for organizations (e.g., 200.23.16.0/23).
Slide 8: Hierarchical Addressing
1. Purpose:
- Simplifies routing by aggregating IP addresses.
- ISPs advertise routes for large blocks of addresses instead of individual ones.
2. Example:
- Organizations under an ISP share a common prefix (e.g., 200.23.x.x).
- Reduces complexity in routing tables.
