DHCPv4 / DHCPv6
DHCP supplies addressing and configuration. Client, server and relay roles have distinct destination ports; DHCPv6 does not replace IPv6 router advertisements.
Scope: DHCPv4 / DHCPv6 — requirements depend on the selected profile.
protocol · Catalog reviewed 2026-10-21
Infrastructure Requirements
- Address pools and options appropriate to each subnet
- reachable servers or relays
- correct client/relay roles
- separate IPv6 router-advertisement planning.
Network & Physical Requirements
| Port / allocation | Transport | Connection / signal flow | Feature and requirement | Evidence |
|---|---|---|---|---|
| 67 | UDP | Client / relay → DHCP server | Profile requirement · Core DHCPv4 requests / relay to server DHCPv4 | Source checked 2026-09-27 RFC 2131, Section 4.1: Constructing and sending DHCP messages |
| 68 | UDP | DHCP server / relay → DHCP client | Profile requirement · Core DHCPv4 replies to client DHCPv4 | Source checked 2026-09-27 RFC 2131, Section 4.1: Constructing and sending DHCP messages |
| 547 | UDP | DHCPv6 client / relay → DHCPv6 server | Optional · IPv6 DHCPv6 client/relay to server DHCPv6 | Source checked 2026-09-27 RFC 8415, Sections 7.1 and 7.2: multicast addresses and UDP ports |
| 546 | UDP | DHCPv6 server / relay → DHCPv6 client | Optional · IPv6 DHCPv6 server to client DHCPv6 | Source checked 2026-09-27 RFC 8415, Sections 7.1 and 7.2: multicast addresses and UDP ports |
| 67 | UDP | DHCP server → DHCP relay agent (giaddr) | Profile requirement · DHCP relay DHCPv4 server replies to a relay agent DHCPv4 relay deployment | Source checked 2026-10-21 Section 4.1: nonzero giaddr, server replies to relay server port |
| 547 | UDP | DHCPv6 server → DHCPv6 relay agent | Optional · DHCPv6 relay DHCPv6 server replies to relay agent DHCPv6 Relay-reply traffic from a server to the configured relay agent. Relay agents listen on UDP 547. Scope this rule to the configured server and relay addresses; direct server replies to a client use UDP 546. | Source checked 2026-10-21 Sections 7.2 (UDP Ports) and 9.2 (Relay-reply)RFC 8415, November 2018 |
Gotchas & IT Notes
- ⚠DHCP broadcasts do not cross routers without an intentional relay. Scope helper configuration, VLAN and trusted server ports.
- ⚠Static addressing can remove the client requirement; reservations and lease/DNS behavior remain project choices.