There is a small issue that I noticed in the UAP-AC-PRO firmware images — I’ve posted this issue on the community forums and also filed a tracker report. It’s a shell script (or incomplete image) type of error depending on how you look at it but if you SSH into the AP you’ll notice this trace file:

home-BZ.v4.3.28# cat /tmp/rc.txt
...
+ [ -e /usr/etc/rc.postconf ]
+ [ -e /etc/ltecfg/lteUpgradeSierraWireless.sh ]
+ init -q
+ bgnd -r garp -- /sbin/garp -s 2
ERROR: bgnd: EXEC FAILED! Executable: /sbin/garp

If you check to see where this binary executable exists on the firmware image itself, it turns out it is indeed missing:

# echo $PATH ; which garp ; ls -l /sbin/garp
/usr/bin:/bin:/usr/sbin:/sbin
ls: /sbin/garp: No such file or directory

And if you look at which shell script is responsible for this error message (it’s an rc startup script):

# grep -in '' /etc/rc.d/rc
...
92:start() {
93:	# assumes a good starting point (module unloaded, processes stopped)
94:
95:	# update running config
...
194:	# done.
195:	bgnd -r garp -- /sbin/garp -s 2 &
196:	# NOTE: we didn't set the LED here. instead, we rely on the management agent (mcad)
197:	# to call syswrapper.sh:set-ready
...
215:	# make new /etc/inittab takes effect
216:	init -q
217:}
...

–
Either the image needs to include this referenced binary or the shell script needs extra logic to determine when to call the gratuitous ARP command successfully!