Flint2 - Unable to access Synology NAS from 2,5Gb port

Technical Support for Routers
1

Hello,
I recently installed my Flint 2 and it works perfectly fine, except for one point. I cannot access my Synology NAS from my computer when the computer is connected to the 2,5Gb port.

I have the 4.6.6-op24 Firmware version (from GL iNet) installed on the Flint 2.

Short summary of my network to make it easier to understand:

I did not deeply change the configuration of the Flint 2. I simply configured some address reservation and changed DNS to cloudflare.

The WAN port of the Flint2 is connected to my Internet provider box. The Flint 2 WAN IP is defined as DMZ. Everything is turned off on my Internet provider box (Wifi, DHCP, etc....), it just gives Internet access to my main router, the Flint 2.

My computer is connected to WAN/LAN 1 port, so it can have 2,5Gb.
The LAN 2 port is connected to a gigabit non managed switch and the Synology NAS is connected to this Switch, with other devices (home assistant server, etc...) also connected to the switch.

Internet provider box : 192.168.1.1 (DMZ => 192.168.1.253)

Flint 2 Wan IP : 192.168.1.253

Flint 2 Router IP : 192.168.0.100
Synology IP : 192.168.0.169
Computer : 192.168.0.110

In this configuration, when I try to connect to the Synology admin interface (192.168.0.169:5000 or 5001 in https), I get a timeout... I see a redirection from 5000 to 5001 and it does not load in the end.
I can ping the Synology from the computer, it works. I can also connect to my home assistant server (which is also connected to the switch) without any problem, the same for proxy manager etc...

The ports 5000 and 5001 seem to be ok also...

Test-NetConnection 192.168.0.169 -Port 5000
ComputerName : 192.168.0.169
RemoteAddress : 192.168.0.169
RemotePort : 5000
InterfaceAlias : Ethernet 2
SourceAddress : 192.168.0.110
TcpTestSucceeded : True

Test-NetConnection 192.168.0.169 -Port 5001
ComputerName : 192.168.0.169
RemoteAddress : 192.168.0.169
RemotePort : 5001
InterfaceAlias : Ethernet 2
SourceAddress : 192.168.0.110
TcpTestSucceeded : True

The strange thing is that if I connect my computer to the switch, then it works perfectly, but I would be restricted to 1Gb in that case due to the switch.
So it seems there is some non working connection between the 2,5Gb port and the other 1Gb ports on the Flint 2 but I am really not experienced enough to determine if it is a bug or a feature :slight_smile:

Do I miss something ? Or maybe it is an option on the NAS that prevent the connection in that case ? But 2,5Gb or 1Gb port, it should be the same behavior...

Thanks a lot.

2

I solved my problem on my own. Here is the solution in case someone would have the same problem one day.

After some testing, I found that it is because I activated, long time ago, the jumbo frames on my Synology NAS (MTU 8000). I switched back to MTU 1500 and it works fine now, the NAS is reachable again from the 2,5Gb port. But I never had such problem with my previous router...

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