Unreachable nodes in a mixed lan wlan network

Question

I have a home Network starting with my Internet router which contains 300 MBit/s WLAN and a 4 port Gigabit Switch (FB7390).

Attached to that Switch there is anoter 5 port Gigabit Switch. It was necessary because of the 5 Computers, the smart TVs, the smart meter Raspberry Pi and the NAS Storage in the cellar. So some of these devices are on the router itself, some on the cascaded Switch.

Downstairs the WLAN was so bad so i installed another WLAN repeater to extend the bandwidth (FR300e). Attached to that repeater there are two raspberry Pis doing some home Automation stuff.

All devices have dhcp activated. All devices appear in the main router UI as active nodes with unique MAC and IP adresses.

Now the Problem: Some devices can ping or ssh one of the downstairs WLAN Pis and some can not. Especially the one that is in the same WLAN repeaters Network can always.

The important one (the smart home central node) can not always.

I made a Long term ping analysis an found out

29.08.2015 12:18:03 Average roundtrip time is 4 ms. 50% losses.
29.08.2015 12:17:34 100% losses.
29.08.2015 12:17:03 Average roundtrip time is 5 ms. 50% losses.
29.08.2015 12:16:34 100% losses.
29.08.2015 12:16:03 Average roundtrip time is 5 ms. 50% losses.
29.08.2015 12:15:34 100% losses.
29.08.2015 12:15:03 Average roundtrip time is 3 ms. 50% losses.
29.08.2015 12:14:34 100% losses.
29.08.2015 12:14:03 Average roundtrip time is 3 ms. 50% losses.

And some times much worse (100% loss).

At the same time the two WLAN Pis can talk without losses to each other.

What can be the reason for this? How can i get a reliable Network Connection?

Edit:

I got some new test results. I pinged from hop to hop from both sides and found out what I never would have guessed: When I ping from the garden's pi to the WLAN gateway I get a very low packet loss. When I go further to the main router it's the same.

When I ping the main router from the home automation pi I get very quick answers an no packet loss. (1 GBit LAN)

So I have two pis that can ping the central router they are somehow attached to with no or few packet loss - but when I ping from one to another I get over 90% packet loss.

Answer 1

Sounds like your downstairs repeater is doing NAT, which acts as a kind of a poor man's firewall that blocks incoming connections from the upstream side of the NAT. Make it not do NAT.

Answer 2

Think I found the answer. My NAS had been set up to be the IPV6 Gateway by default when enabling IPV6. Since I turned this off the problems disappeared.

All this IPV6 stuff is too complicated, hope there will be easier solutions in the future!