There is a problem with the DES 3828 switch, everything is fine on the local network, the sites do not open. What is the reason?

Question

Computer networks

There is a MicroTIK router, with an Internet connected to it. There are also 3 switches connected in series. on the first switch everything is OK. The problem, as I mean, is in 3828, even if you directly plug a router and a computer through it - there is no Internet. Correct IPs are bound, servers work stably, port 80 opens on the router, sites ping, but do not open, what could be the reason?

Answer 1

mtu look.