They are not really boolean, because we have both ipv4 and ipv6, but
for each protocol we have either unset, no, and yes.
From https://github.com/systemd/systemd/issues/13316#issuecomment-582906817:
LinkLocalAddressing must be a boolean option, at least for ipv4:
- LinkLocalAddressing=no => no LL at all.
- LinkLocalAddressing=yes + Static Address => invalid configuration, warn and
interpret as LinkLocalAddressing=no, no LL at all.
(we check that during parsing and reject)
- LinkLocalAddressing=yes + DHCP => LL process should be subordinated to the
DHCP one, an LL address must be acquired at start or after a short N
unsuccessful DHCP attemps, and must not stop DHCP to keeping trying. When a
DHCP address is acquired, drop the LL address. If the DHCP address is lost,
re-adquire a new LL address.
(next patch will move in this direction)
- LinkLocalAddressing=fallback has no reason to exist, because LL address must
always be allocated as a fallback option when using DHCP. Having both DHCP
and LL address at the same time is an RFC violation, so
LinkLocalAdressing=yes correctly implemented is already the "fallback"
behavior. The fallback option must be deprecated and if present in older
configs must be interpreted as LinkLocalAddressing=yes.
(removed)
- And for IPv6, the LinkLocalAddress option has any sense at all? IPv6-LL
address aren't required to be always set for every IPv6 enabled interface (in
this case, coexisting with static or dynamic address if any)? Shouldn't be
always =yes?
(good question)
This effectively reverts 29e81083bd. There is no
special "fallback" mode now, so the check doesn't make sense anymore.
The configuration of networkd has a DHCPv6Client setting in its
[IPv6AcceptRA] section, which, according to the man page, can be
a boolean, or the special value "always". The man page states
that "true" is the default.
The default value is implemented in src/network/networkd-network.c
by setting field ipv6_accept_ra_start_dhcp6_client of network to
true. However, this field is not a boolean, but an enum type
IPv6AcceptRAStartDHCP6Client (src/network/networkd-ndisc.h).
Setting ipv6_accept_ra_start_dhcp6_client to true effectively
corresponds to the enum value IPV6_ACCEPT_RA_START_DHCP6_CLIENT_ALWAYS,
resulting in the DHCPv6Client setting having the default value
"always".
This patch changes the initialisation to the correct enum value
IPV6_ACCEPT_RA_START_DHCP6_CLIENT_YES.