DHCP support in ifupdown is severely outdated:

1) The interfaces(5) manual page states that:

DHCPv4 support: "dhclient, pump, udhcpc, dhcpcd. (They have been listed in their order of precedence.)"

$ LC_ALL=C apt-cache search dhcp | grep client | grep -v dbgsym | grep -v dev | sort
dhcpcanon - DHCP client disclosing less identifying information
dhcpcd5 - DHCPv4, IPv6RA and DHCPv6 client with IPv4LL support
dibbler-client-dbg - portable DHCPv6 client
dibbler-client - portable DHCPv6 client
isc-dhcp-client-ddns - Dynamic DNS (DDNS) enabled DHCP client
isc-dhcp-client - DHCP client for automatically obtaining an IP address
openstack-cluster-installer-cli - automatic PXE and puppet-master installer for OpenStack - API client
udhcpc - Provides the busybox DHCP client implementation
wide-dhcpv6-client - DHCPv6 client for automatic IPv6 hosts configuration

Two of the DHCP clients supported by ifupdown no longer are in the archive (pump, dhcpd). The later may have been replaced by dhcpcd5, but the man page isn't clear on whether this is supported. The man page probably needs to be updated.

DHCPv6 support: The man page suggests that only dhclient is supported. However wide-dhcpv6-client is mentioned earlier as possibly providing its own hooks. The man page probably needs to be updated.

2) Upstream will discontinue the ISC DHCP codebase by the end of 2022.

a) ifupdown will have to implement support for some of the alternatives listed at <https://www.isc.org/blogs/dhcp-client-relay-eom/> before Bookworm is released.

b) Debian will have to select a replacement for isc-dhcp-client as its stock Priority:Important DHCP client to ship. By all counts, dhcpcd5 seems to have the best potential for this. However, I find its "Recommends: openresolv | resolvconf" excessive. This should be Suggests at most.

Best Regards,

Martin-Éric
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This is still broken.

"dhclient, udhcpc, dhcpcd. (They have been listed in their order of precedence.)"

This really is a problem if someone wants to use udhcpc or dhcpcd, because dhclient is installed by default, so it always gets used. ifupdown really needs a way to configure the precedence order.

Martin-Éric

- -- System Information:
Debian Release: 12.0
  APT prefers testing-security
  APT policy: (500, 'testing-security'), (500, 'testing-debug'), (500, 'stable-security'), (500, 'testing')
Architecture: i386 (i586)

Kernel: Linux 6.1.0-9-686 (SMP w/1 CPU thread; PREEMPT)
Kernel taint flags: TAINT_CPU_OUT_OF_SPEC
Locale: LANG=fi_FI.UTF-8, LC_CTYPE=fi_FI.UTF-8 (charmap=UTF-8), LANGUAGE=fi:en
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages ifupdown depends on:
ii  adduser   3.132
ii  iproute2  6.1.0-2
ii  libc6     2.36-9

Versions of packages ifupdown recommends:
ii  dhcpcd-base [dhcp-client]  9.4.1-21

Versions of packages ifupdown suggests:
ii  ppp     2.4.9-1+1.1+b1
pn  rdnssd  <none>

- -- debconf information:
  ifupdown/convert-interfaces-hotplug: true
  ifupdown/convert-interfaces: true
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El 15/05/23 a las 14:17, Martin-Éric Racine escribió:

Indeed. I will work on this after the upcoming release.

Thanks for pointing this out,

As discussed in bug #1038882, ifupdown needs to change its precedence order for DHCP clients. The new order of precedence should be: dhcpcd, dhclient, others (see above). This is necessary to ensure that dhcpcd-base will become the new default DHCP client after upgrades.

Martin-Éric
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