<div dir="ltr">Hi Thomas Haller<div> <div>Thanks for your valuable information and clarification. I tested the behaviour of a change in IPv4 address at device side, when another device is in link local network for the same static IPv4 address. </div><div> </div><div><div><div dir="ltr" class="gmail_signature" data-smartmail="gmail_signature">Regards Manjunatha Srinivasan N</div></div> </div></div></div> <div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Thu, 19 Oct 2023 at 18:04, Thomas Haller <<a href="mailto:thaller@redhat.com">thaller@redhat.com</a>> wrote: </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">On Thu, 2023-10-19 at 17:48 +0530, manjunatha srinivasan wrote: > Hi > I have 2 following ethernet profiles at /etc/NetworkManager/system- > connections: btw, you can also enable LL additionally with DHCP. Then DHCP is attempted in the background, while you always have a LL address. See "ipv4.link-local" setting in `man nm-settings`. That is IMO better than two profiles. > One for dynamic ip configuration and other for link local as fallback > when DHCP server is not reachable. As expected when DHCP server is > not reachable, fall back IPv4 address happens e.g. 169.254.105.20 > with subnet mask as 255.255.0.0 by the NetworkManager. > This particular IP address is always the same which is expected one. > Please let me know how this constant IPv4 address is decided by the > NetworkManager. IPv4LL is documented by RFC <a href="https://datatracker.ietf.org/doc/html/rfc3927#section-2.1" rel="noreferrer" target="_blank">https://datatracker.ietf.org/doc/html/rfc3927#section-2.1</a> The code is here: <a href="https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/blob/94ead251ded1ed7d3a1ea9953f041708daf3787f/src/core/nm-l3-ipv4ll.c#L382" rel="noreferrer" target="_blank">https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/blob/94ead251ded1ed7d3a1ea9953f041708daf3787f/src/core/nm-l3-ipv4ll.c#L382</a> It basically hashes the MAC address and a generation counter. > Also let me know if there is any configuration option in > NetworkManager to change last 2 octets (i.e.105.20) represented in > the decimal value of last 2 values of ethernet MAC hex address. The address couldn't be fixed, because there is always the possibility that another host on your network already picked this address. It falls back to a retry via the generation counter. In any case, there is no option in NetworkManager (or RFC) to influence the IPv4LL address in a more immediate way. > > Ethernet (eth0) method based on DHCP: > [connection] > id=my-eth0 > uuid=8466b654-0183-4900-a2d6-26a9e6af275e > type=ethernet > autoconnect-priority=1 > interface-name=eth0 > timestamp=1697699281 > > [ethernet] > > [ipv4] > dhcp-timeout=10 > method=auto > > [ipv6] > addr-gen-mode=stable-privacy > method=auto > ra-timeout=10 > > [proxy] > ------------------- > Ethernet (eth0) method based on link-local: > root@FXR90D5FB72:/etc/NetworkManager/system-connections# cat rfid- > ll-eth0.nmconnection > [connection] > id=ll-eth0 > uuid=f07f43e6-59c8-428f-bc04-55a0e581e621 > type=ethernet > interface-name=eth0 > > [ethernet] > > [ipv4] > method=link-local > > [ipv6] > addr-gen-mode=stable-privacy > method=auto > > [proxy] > ------ > > When DHCP request fails, the IPv4 address fallback to > > > > Thanks & Regards > Manjunatha Srinivasan N </blockquote></div>