Reach a server through a relay
02A relay carries DHCP between a client’s local network and a server elsewhere. Its giaddr field supplies relay context.
Related RFCs and changes
“Updates” changes part of an earlier RFC. “Obsoletes” replaces it. This list shows selected related documents.
DIAGRAM§ 4.1 ↗
RFC 2131 · § 4.1EXAMPLE
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03
Return to the correct client link.
The server responds to the relay, which delivers the response locally.
Protocol participantThreat or exceptionProtocol controlSimplified drawings · precise section references
Read the updated RFC section ↗
Broadcast scope need not limit server placement.
- DHCP uses UDP server port 67 and client port 68.
- A relay populates giaddr when forwarding a client request.
- With nonzero giaddr, the server sends return messages to the relay’s DHCP server port; the relay forwards to the client.
Relay and server policy determine address selection. This example does not imply that relays authenticate every client or that any relay-supplied field can be trusted without deployment controls.
Read the RFC section ↗Diagrams simplify the RFC. Read the linked sections for complete requirements.
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