Firewall blocking ethernet access to NAS - but not wifi access

I recently replaced a Linksys wifi modem/router (it failed completely) with a new Netgear N600 wifi modem/router.

I'm having some odd problems accessing a Synology NAS HDD on my LAN - I never had these problems with the Linksys router/modem ...

1. The only connection problem I see relates to the Synology NAS HDD. All internet connections work fine. I see the same problem connecting from a browser (Firefox, Chrome, Safari) and directly from Time Machine.

2. If I connect to the Netgear modem/router by wifi, I can connect with Firefox to the NAS by IP address and URL. This is the case with the iMac (Yosemite 10.10.1) firewall on and off.

3. If I connect to the Netgear modem/router by ethernet, I can connect with Firefox to the NAS only by IP address but not by URL. This is the case with the iMac firewall on.

4. If I turn the iMac firewall off and connect to the Netgear modem/router by ethernet, I can connect with Firefox to the NAS by IP address AND by URL.

So, iMac firewall off, no connection problems at all.

Firewall on, ethernet connection by url blocked but wifi connection by url allowed. Connection by IP address allowed via ethernet and wifi with firewall on and off.

This seems to confirm it is an issue with the iMac firewall not liking something coming from the NAS HDD via the modem/router.

Incidentally, I see the same problem with a Macbook ...

I guess I could just run with the iMac firewall off as the Netgear router/modem also has a firewall - except I have a lot more faith in the Mac firewall.

Any suggestions?

Thanks,

Larry

iMac, OS X Yosemite (10.10.1), iMac (20-inch, Early 2008)

 

I noticed from the firewall log that some incoming UDP requests were being ignored because the firewall was in Stealth Mode.

Turned off the firewall Stealth Mode and everything is working properly ... ?

Not entirely happy about Stealth Mode being off but it is much better than turning the whole firewall off.

My understanding is that when in Stealth Mode, the firewall ignores UDP requests from "closed" ports?

So, I guess the Netgear router/modem is using a UDP port that the iMac thinks should be closed?

Any suggestions for a "proper" solution?

Thanks,

Larry