Can't ping one PC from another PC. Actiontech MI424WR

[Serniks]

Can't ping one PC from another PC on my home network connected to Actiontech MI424WR.

I have 4 PCs in my network.

All PINGs,  router->PC  and PC->router,   work fine.  

Internet connection is fine.

However, no one PC can ping or see another PC in the network.

If I take additional switch (Netgear 5 ports),  connect all 4 PC to the switch, and connect the switch to the router - everything works fine. Now one PC can see and ping another PC on network.

What could be the problem with router? Why the connection between different sockets on the router lost?

Thank you. 

[Anti-Phish1]

From the fact that it works with an external switch, I have to conclude that your router is bad.

The 4 ports on the router are in fact a switch and should operate just like the external switch you tried.

[smith6612]

What revision of the MI424WR router do you have? There has been some talk lately about a "Hardware Acceleration" option in the web administration for the Rev. I causing issues if it is unchecked. I believe you may find this in the advanced home network settings. This setting started to show up around the time IPv6 support did in the router.

Just a thought.