Short note: DHCP

Short answer

DHCP automatically assigns IP addresses and network settings via DORA process (Discover, Offer, Request, Acknowledge) using UDP ports 67/68. It provides lease-based allocation with renewal at 50% lease time, supports dynamic/automatic/manual allocation, and uses relay agents for cross-subnet communication.

Write a short note on DHCP.

DHCP (Dynamic Host Configuration Protocol, RFC 2131) automatically assigns an IP address and other network settings to a host when it joins a network, so an administrator need not configure every host manually. It runs on UDP: the server uses port 67 and the client uses port 68. It is an extension of BOOTP.

Information supplied

IP address, subnet mask, default gateway, DNS server addresses, lease time.

Operation: DORA

 Client                        DHCP server
   |--- DISCOVER (broadcast) ------>|
   |<-- OFFER (IP, mask, lease) ----|
   |--- REQUEST (accept offer) ---->|
   |<-- ACK (confirmed) ------------|

Discover: client broadcasts (src 0.0.0.0, dest 255.255.255.255) to find servers.
Offer: server offers an unused IP address and lease time.
Request: client requests the offered address (and informs other servers).
Acknowledge: server confirms and the client configures its interface.

Features

Lease: the address is given for a limited time; the client renews at 50 % of the lease (T1). On expiry the address returns to the pool.
Allocation methods: dynamic, automatic, manual (static by MAC).
A relay agent on a router forwards DHCP messages to a server on another subnet.
Advantages: less configuration work, fewer address conflicts, efficient reuse of addresses, mobile users supported.

✓ Answer checked by Claude Opus 5.5 (high effort)

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