Good Evening,
Usually the Client will renew the DHCP-Lease before it expires.
To be more precise, after 50% of the Lease time, the Client will enter the Renewal Period.
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In your Case:
If your DHCP-Server has a lease time of 12 hours...
Your Client will "Renew" the lease automatically after 6 Hours.
To check your Leases in RouterOS :
/ip dhcp-server lease print active
No active* Lease should have a value smaller then 6Hour under the Parameter "EXPIRES-AFTER"
(*active means Clients wo are connected and active in the Network)
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If this doesn't happen, you have a Problem in your Network..
Possible Problem:
- Multiple Client with the same Name
- Client with illegal characters in Netname
- Multiple Client with the same MAC
- Multiple DHCP-Servers
- Firewall