When you upgrade your Solaris system from 11.3 to 11.4, you may find that things don’t go well if you have configured the ARP property on the loopback interface (regardless of value, on or off).
This is a little surprising as the ARP property for a loopback interface does not exist in Solaris 11.4. This might be a common problem if you are using the integrated load balancer (ilb) and have configured Direct Server Return (DSR) load balancing. If so, you may recall that you needed to set the ARP property to off in order for a correct DSR setup of the virtual IP address on your load balanced member servers.
If ARP has been set (again, either on or off), when you boot into Solaris 11.4 after upgrading, you’ll find that your loopback interface addresses are all disabled, which of course causes all sorts of problems, including that your primary network interfaces likewise probably won’t be operational.
I’ve reproduced this with a vanilla stock install of Solaris 18.104.22.168.3 upgrading to 22.214.171.124.0.
Solaris 11.4 does away with the network configuration management stored outside of the SMF (previously stored in /etc/nwam, /etc/ipadm, and /etc/dladm). These properties are now persisted in svc://network/ip-interface-management:default (the ip interface settings anyway).
If you’ve stepped into this problem, you’ll notice that you can manually correct the interfaces with ipadm, but you’ll be right back into the same boat if you reboot your server. In order to permanently correct this issue, you need to delete the errant property from the SMF:
svccfg -s network/ip-interface-management:default delprop interfaces/lo0/ipv4/arp delprop interfaces/lo0/ipv4
A reboot after the above changes is the simplest final step. Everything should be clear.
If you haven’t yet upgraded to Solaris 11.4, you can clear the arp property ahead of time with:
ipadm reset-ifprop -p arp -m ipv4 lo0
However, note that if you are using DSR load balancing, you might cause issues just as soon as you reset this property.