Device: CCR2116-12G-4S+
Architecture: arm64
Use case: ISP NAS (DHCPv4-server + RADIUS + VRRP)
RouterOS versions tested:
- 7.16.2 (stable) — works reliably
- 7.20.2 / 7.20.6 (stable) — intermittent issue observed
Configuration overview:
- DHCPv4-server running on VRRP interface
- use-radius=yes
- Static IP assignment via RADIUS (Framed-IP-Address)
- address-pool=static-only
- Only one active DHCP server in the broadcast domain (verified)
Problem description:
On RouterOS 7.20.x DHCPv4-server works in general, but intermittently fails to assign
RADIUS-provided static IP addresses.
The following log message appears occasionally:
"dhcp,critical,error failed to assign ip : already in use"
At the same time, ARP table may contain stale or failed entries for the same IP address.
The IP address belongs to the same client MAC and no actual duplicate client or IP conflict exists.
The issue is not constant and does not affect all clients.
It is observed sporadically, most often after client reconnects or VRRP role changes.
Expected behavior:
DHCPv4-server should successfully assign a RADIUS-provided static IP address when
the IP/MAC binding already exists and no real conflict is present.
This behavior is observed consistently on RouterOS 7.16.2 under the same configuration and load.
Result / workaround:
After downgrading RouterOS from 7.20.x back to 7.16.2, the issue disappears completely.
The system operates stably with identical configuration and traffic conditions.
Conclusion:
This appears to be a regression introduced after RouterOS 7.16.x,
possibly related to DHCPv4-server conflict detection or ARP handling logic
in environments using VRRP together with RADIUS-based static IP assignment.