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RFC 2131, "Dynamic Host Configuration Protocol", March 1997

Note: This RFC has been updated by RFC 3396, RFC 4361, RFC 5494, RFC 6842

Source of RFC: dhc (int)

Errata ID: 5100
Status: Rejected
Type: Technical
Publication Format(s) : TEXT

Reported By: Fan Wei
Date Reported: 2017-08-29
Rejected by: Eric Vyncke
Date Rejected: 2024-04-23

Section 4.1 says:

Normally, DHCP servers and BOOTP relay agents attempt to deliver
DHCPOFFER, DHCPACK and DHCPNAK messages directly to the client using
uicast delivery.

It should say:

Normally, DHCP servers and BOOTP relay agents attempt to deliver
DHCPOFFER, DHCPACK messages directly to the client using
unicast delivery.


According to prior part description in section 4.1: "In all cases, when ’giaddr’ is zero, the server broadcasts any DHCPNAK messages to 0xffffffff.", the DHCP server should not send DHCPNAK in unicast to client unless 'giaddr' is not zero.
DHC WG feedback on this errata is:
"What's possibly being missed here is that the DHCP server has the client's MAC address, and is not relying on just on the routing table in the kernel, but also on giaddr and chaddr to determine how to send unicast responses. If giaddr is nonzero, the server sends the response using regular unicast through the IP stack's routing table, but if giaddr is zero, the server constructs a layer 2 frame with chaddr as the layer 2 destination address and unicasts that frame out the appropriate interface, bypassing the kernel's routing table and layer 3 processing entirely. So it doesn't actually matter what the IP destination address is other than that the client stack has to recognize that address as its own. The 'broadcast' bit takes care of the case where the client isn't able to do this. The server is always permitted to broadcast if it doesn't have the ability to route the response directly over layer 2, but at the time this RFC was written this was considered suboptimal, and the RFC goes to some lengths to make it possible for DHCP servers and relay agents to avoid sending broadcasts"

I.e., the current text is correct.

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