Close Out Report
The problem/symptom was on two machines–iMac and a MacBook Pro both with up to date OS’s failing to activate mounts (shares) with a Synology NAS (relatively new with up to date OS) on waking from sleep. Before going into sleep, all the mounts worked well. On waking the machines would not recognise the mounts. The Automounter app said “Mounting…” and would eventually time out. The Mountain app didn’t respond. Using the “mount” command in the Terminal would show the shares mounted. Finder would “beach-ball” when clicking on the server. The only way to resolve things I could find would be to re-boot the computers.
I assumed the problem cause resided with the Macs OS or the NAS. I rejected thinking it was hardware related since the odds of failure on the two Macs was low. Cast out for ideas here and with friends. Only when @csf111 came along (after I had given up!) and logically going through it was the role of the Netgear GS108 network switch considered.
@csf111 suggested changing a couple of settings on the switch, assuming it was a “managed” switch. It wasn’t. The GS108 is an unmanaged switch. So to enable this path of solution to progress I purchased a new GS308E Netgear managed switch (8-port) to replace the GS108. Simple to replace–just start up the new switch, move the Ethernet wires. Shutdown and store the old switch. Simple.
I ran a number of tests to try to ascertain which of the settings suggested by @csf111 might be the culprit. All those tests I did, with erroneous conclusions, were flawed (didn’t realise it at the time) because it did not occur to me to have to re-start the switch between changing the config settings. The switch’s web page didn’t remind me, not that it was Netgear’s fault to not tell me that. These flawed tests suggested things working, but turned out not. After an over-night sleep, the “beach-ball” returned on the iMac. It occurred to me that my tests were flawed since I did not re-boot switch between changes. Yes, slapped my head in disgust with not thinking of that!
New switch settings:
Broadcast filtering: enabled. Enabled out of the box.
IGMP Snooping: disabled. ← believe this the critical change. Enabled out of the box.
On re-starting switch without re-staring either Macs, mounts came back “automagically”.
Conclusion: IGMP Snooping must be “disabled” on the network switch connecting the Macs with the Synology NAS, else proper “waking” of Macs from sleep won’t reconnect reliably and/or at all. @csf111 explained what “IGMP snooping” is:
At an abstract level, IGMP snooping monitors IP
multicast traffic. SO, it watches the “dialog” with
all your mounts, and after a while goes, “Ah, you
haven’t used these in a while, shut’em down Dano”
I did not investigate Broadcast filtering (the other setting change suggested by @csf111) having decided to leave well enough alone now as all seems to be working.
Happy camper. Thanks @csf111