07.01.2025 06:01, Muggeridge, Matt wrote:
I have two systems where I need them to assign link-local addresses in a
169.254.4/24 subnet, regardless of any other addresses configured. I'm using a
/24 subnet because I have multiple interfaces on the system that require
link-local addresses; I was placing them in their own subnets.
From this
comment<https://www.freedesktop.org/software/systemd/man/latest/systemd.network.html#:~:text=If%20an%20IPv4%20link%2Dlocal%20address%20(169.254.0.0/16)%20is%20specified%2C%20IPv4%20Address%20Conflict%20Detection%20(RFC%205227)%20is%20enabled%20for%20the%20address.>
in the man page, I was expecting I could configure the interface address identically
on both systems and leave it to collision detection to pick an appropriate available
address.
The 1st interface assigns its link-local address (169.254.4.2/24).
Unfortunately, the next interface to start doesn't assign any link-local
address. I've tried to get more debug information by increasing log-level to
debug, but I get no indications around the address assignments.
As an experiment, I change the 2nd system to use a different host address in
the same subnet, and it gets assigned correctly. I guess that collision
detection is preventing the address assignment.
How do I achieve this or how can I get more debug information?
The relevant snippet from the network config file is:
[Network]
Address=169.254.4.2/24
This is not "dynamic link-local address". It is the fixed address you
assigned. If this address is not available, why do you expect
systemd-networkd to silently substitute it with another one?
Link local addressing is more than just the specific prefix. It is a
separate procedure to configure interface that follows well defined
rules for selecting addresses to use. You cannot really mix it with
fixed address assignment.
What could be done is supporting something like
Address=169.254.4.0/24
with the semantic "pick any unused address in this range".
Full contents of the network configuration follows:
$ networkctl cat 10-eno0.network
# /etc/systemd/network/10-eno0.network
[Match]
KernelCommandLine=!nfsroot
Name=eno0
[DHCP]
ClientIdentifier=mac
RouteMetric=10
UseDomains=yes
UseHostname=yes
UseMTU=yes
[IPv6AcceptRA]
UseRedirect=no
[Link]
RequiredForOnline=no
[Network]
DHCP=yes
Domains=labs.company.net
NTP=10.10.135.123
# LinkLocalAddressing=yes
# IPv4LLStartAddress=169.254.1.1
Address=169.254.4.2/24
# /usr/lib/systemd/network/10-eno0.network.d/10-network.conf
[Network]
MulticastDNS=yes
Regards,
Matt.
