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dhcp: allow to not send client-id (option 61) in IPv4

Íñigo Huguet requested to merge ih/dhcp-client-id-none into main

Summary

Add new special value "none" to ipv4.dhcp-client-id to allow not to send any DHCP Client-ID (Option 61), instead of sending a default generated one.

Purpose

Sending a client-id is not mandatory according to RFC2131. It is mandatory according to RFC4361 that superseedes it.

Some weird DHCP servers conforming RFC2131 can get confused and break existing DHCP leases if they start receiving a client-id when it was not being previously received. Users that were using other DHCP client like dhclient, but want to use NetworkManager's internal DHCP client, can suffer this problem.

Add "none" as accepted value in ipv4.dhcp-client-id to specify that client-id must not be sent. Note that this is generally not recommended unless it's explicitly needed for some reason like the explained above.

Client-id is mandatory in DHCPv6.

RHEL-1469
NetworkManager-ci!1525 (merged)

Checklist

Please read https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/blob/main/CONTRIBUTING.md before opening the merge request. In particular, check that:

  • the subject for all commits is concise and explicative
  • the message for all commits explains the reason for the change
  • the source is properly formatted
  • any relevant documentation is up to date
  • you have added unit tests if applicable
Edited by Íñigo Huguet

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