(UDP) Packet Fragmentation not working correctly with 3.4.3.8.088 (RT-N56U)?

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What steps will reproduce the problem?
1. Coming from previous FW Version on RT-N56U, which had no problems in this 
case so far
2. Now my PS4 complains about the Router not supporting Packet Fragmentation 
(and i check this often, and this was the first time appearing and the only 
thing changed since the last PS4 Network-Test was the Routers Firmware-Version).
3. I found this issue from 2012 which seems pretty identical:
https://code.google.com/p/rt-n56u/issues/detail?id=277
4. Even "dirty-flashing" back to the previous Firmware did not resolve this?! 
Didn't have time yet to test it with a complete reset and re-flashing the older 
version, and i'd like to keep away from that for time-reasons. ;)
5. My ISP is a cable-provider in Germany (UnityMedia), i got a 
business-contract, pure IPv4-connection with my own subnet and a static IP so 
the RT-N56U is the device sitting on the public IP-Address, pretty much nothin 
"in its way" besides the modem, which pretty much does nothing in terms of 
networking - no nat, dhcp, dns or whatever...

If you could please have a look into it (has to be something in your latest 
code-contributions, doesn't it? ;) ) and if you find something, fix it?

Thanks in advance and keep going on this great Firmware, your work is pretty 
amazing! :)

Original issue reported on code.google.com by bassmasc...@gmail.com on 9 Dec 2014 at 11:56

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I have this issue to with all routers (ASUS RT-N65U, FRITZ!Box 3390, NETGEAR 
Nighthawk) in combination with PS3, PS4 and PS Vita!

In my opinion it is not the router/modem or the internet service provider like 
Unitymedia. The problem is related to the PlayStation Network.

Even if this message appears during the internet connection test on my 
PlayStation device I have not any problems to play games online or to use the 
online features of the PlayStation Network.

The problem should be reported in the official PlayStation forum.

Original comment by pastorel...@googlemail.com on 10 Dec 2014 at 11:45

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Just want to give an update on my latest findings.
I noticed that after updating the firmware as described in the first post some 
displayed gui-settings didn't match the actual config. For example, even if the 
GUI showed SSH disabled, a portscan from my internal network showed the 
SSH-server up, running and reachable. Enabling, saving, disabling and saving 
the SSH GUI-Switch disabled the SSH Server and closed the port. This is just a 
sidenote and had nothing to do with my original problem. ;)

Adding to the first post: I found that having the DDoS-Protection enabled 
somehow limits the MTU. I used http://www.letmecheck.it/mtu-test.php to test 
the connection right to my MODEM. The expected 1500 showed up as a result.
Using the test on my static IP, where the RT-N56U is reachable directly behind 
the modem it showed a far lesser value somewhere in the 145x if i remind 
correctly - can't check right now for the detailed value, but i think it's not 
even that important.
Disabling just the DDoS-Protection (the SYN Protection does not affect 
anything, on a sidenote) allowed the MTU size to the router to be 1500 again. 
That's what i wanted.

So, is this by design or is there an error in the DDoS-Protection-Implemention 
that somehow caps the MTU-Size?

Original comment by bassmasc...@gmail.com on 31 Dec 2014 at 10:49

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Short Update: OP issue seems fixed in 3.4.3.9-091, working fine since updating 
my RT-N56U with the base-version...

Original comment by bassmasc...@gmail.com on 26 Jan 2015 at 2:23