I’m facing a strange issue on my MikroTik network and need some help troubleshooting it

RouterOS General
1

Hello everyone,

I’m facing a strange issue on my MikroTik network and need some help troubleshooting it.

Problem:
Clients are getting “Connected, No Internet” / “Connected without Internet” messages randomly, even though everything appears to be working normally.

Current Situation:

  • Internet is actually working for many sites/services

  • Ping to public IPs (like 8.8.8.8) works

  • DNS seems mostly fine

  • MikroTik CPU/RAM usage is normal

  • No packet loss found in basic tests

  • WAN interface stays connected

  • DHCP is assigning IPs correctly

  • Clients can sometimes browse normally, but Windows/Android still says “No Internet”

  • Issue happens on multiple devices

What I already checked:

  • DNS configuration

  • Gateway reachability

  • DHCP lease settings

  • NAT masquerade rules

  • Firewall rules

  • MTU/MSS

  • FastTrack

  • IPv6 disabled for testing

  • Changed DNS to Google/Cloudflare

  • Rebooted router and ONU

  • Tested with different devices

Environment:

  • Router: MikroTik

  • Clients: Windows + Android

  • ISP connection stable

  • No major bandwidth saturation

Possible Symptoms:

  • Sometimes captive portal detection fails

  • Sometimes apps work but browser shows limited connection

  • Random intermittent issue

Has anyone experienced this before?
Could this be related to:

  • DNS timeout?

  • MTU/MSS issue?

  • IPv6?

  • FastTrack?

  • TCP/UDP blocking?

  • Windows NCSI detection?

  • ISP-side routing issue?

Any suggestions on what else I should check would be appreciated.

Thanks.

2

Check IPv6 MTU and how often prefix expires............. on both ISP and Router side......

3

I don't think that the IPv6 MTU and/or the prefix settings would affect this at all because IPv6 is disabled.

4

Are your clients wired or wireless?

5

Have him answer, also because he requested it and disabling IPv6 does not mean making it disappear from the devices or filtering it into the router, whose configuration is not even known.

6

The answer might be:
Yes.
Yes.
Yes.
Yes.
Yes.
Yes.
Yes.

Just try to reset settings to default ones. Do not tweek and check if problems gone away. If yes, then start reconfiguring step by step doing proper backups to be able to roll back when you figure out problems..