MikroTik + Keenetic: FAQ and Step-by-Step Diagnostics

2025-09-21

This article is compiled as a “cheat sheet” for SOHO/SMB networks: common issues, their symptoms, causes, quick fixes, and diagnostic checklists. Suitable for both engineers and admins who maintain the MikroTik ↔ Keenetic bundle.

📑 Navigation

• EoIP “freezes” when transferring large files
• Site-to-Site VPN is up, but traffic doesn’t pass
• NAT breaks VPN/EoIP
• MTU/MSS: how to choose correctly
• Policy Routing (RouterOS 7)
• SMB from another subnet doesn’t work
• Quick diagnostics checklist
• Command cheat sheet
• Typical MTUs for tunnels
• NAT/Firewall exceptions matrix
• Common pitfalls
• Visualizations
• Resources and documentation

1) EoIP “freezes” when transferring large files

Symptoms: SMB/FTP hangs, speed fluctuates, RDP drops. Causes: incorrect MTU/MSS, fast-path with IPsec, NAT/Firewall errors.

MTU Issue on reg.ru and Its Solution via iptables

2025-08-05

Introduction: A Hidden Network Issue

Developers and system administrators using servers on the OpenStack platform (for example, the C*-M*-D* hosting plans from reg.ru) sometimes encounter mysterious network problems. The internet seems to work, but when trying to transfer large amounts of data or establish connections to certain services, requests may hang or fail due to timeouts.

The provider explains this issue as a feature of their infrastructure:

Servers on the OpenStack platform use VxLAN technology, which reserves 50 bytes for service information. Because of this, the maximum transmission unit (MTU) on the server’s main network interface (ens3) is 1450 bytes.