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Old 04-04-2020, 03:52 AM   #1
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Registered: Apr 2020
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NetworkManager and IPv4LL (link-local)


i am struggling with the following simple case for a while now.

I have a custom embedded Linux board running Debian Buster and using NetworkManager (1.14.6-2+deb10u1) for networking. Now i would like to get a link-local address as fallback whenever DHCP fails on the eth0 device (pretty normal default behavior IMO), but i never get an address in the range assigned - the DHCP case works. Can someone please enlighten me what i am missing?

# interfaces(5) file used by ifup(8) and ifdown(8)
# Include files from /etc/network/interfaces.d:
source-directory /etc/network/interfaces.d
auto lo
iface lo inet loopback


I tried to use the internal dhcp implementation (using libsystemd - as seen in the logs below) since i thought this should minimize issues, but the result is the same as with dhclient and dhcpcd installed (currently i have uninstalled both of them).
dhcpcd seems to be never called at all anyway?

Heres the NM log (journalctl -u NetworkManager) - with mostly removed wifi related stuff:

"nmcli con up eth0" (eth0 is the NM connection profile name)
ends up with
Error: Connection activation failed: IP configuration could not be reserved (no available address, timeout, etc.)

"eth0" connection profile:


Old 04-06-2020, 04:57 AM   #2
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Registered: Apr 2020
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over the weekend i had the following insights:

i created the following wired connections profiles:
nmcli connection add type ethernet ifname eth0 con-name eth0-auto
nmcli connection modify eth0-auto connection.autoconnect-priority 100
nmcli connection modify eth0-auto connection.autoconnect-retries 2 # reduce DHCP retries [since NM v1.6]
nmcli connection modify eth0-auto ipv4.dhcp-timeout 3 # reduce timeout time for each DHCP probe [since NM v1.2]

nmcli connection add type ethernet ifname eth0 con-name eth0-ll
nmcli connection modify eth0-ll connection.autoconnect-priority 50 ipv4.method link-local
This way it seems that NM "falls back" to link-local if no address via DHCP could be aquired.

My initial assumption was that link-local should work as fallback on the same connection, instead of specifying another separate fallback connection.
Can someone confirm if this is the way to go with NM?


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