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DHCP server problem

Thu May 31, 2018 9:05 pm

firstly let me explain my network diagram.
There is a mikrotik router in which port 2 is connected to a d link manageable switch. users are connected from that switch via dummy switch. Recently users are not getting their ip through dhcp.
dhcp server has been configured properly on the router. users were getting ip through dhcp. but now without any changing in the configuration of mikrotik router, users aren't getting ip.
again if a tplink router is connected to the d link switch, users are getting ip through dhcp.

Help me to troubleshoot the problem
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Re: DHCP server problem

Tue Jun 05, 2018 10:15 am

I would start with Tools > Packet sniffer. Set it to save to a file and only capture UDP packets. Click Apply, then Start and renew the IP on a client. Wait 10 seconds and stop the packet capture. Copy the file to your computer and open it with Wireshark. In the list of packets, you should see a Discovery, Offer, Request, Ack. Do you see all 4?

The Discovery is your client looking for DHCP Servers on the network. There should only be 1.
The Offer is your mikrotik offering an IP.
The client will then deny or request the IP. If denying, maybe the client detects an IP conflict however RouterOS detects conflicts too and skips bad IPs.
The Mikrotik will then acknowledge that the client accepted the IP.

Also double check the basics:
- IP > Pool, check the "Used IPs". You out of IPs?
- IP > DHCP Server, is the entry red which denotes a misconfig?
DHCP is on the correct interface?
- Enable log topic DHCP and renew a client, anything interesting in the log?

Finally if still no success, set a static IP and ping the Mikrotik. If you can't ping or do an ARP lookup to find the router, then possibly a physical connection issue or your smart switch is blocking the MAC of the mikrotik.
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Re: DHCP server problem

Wed Oct 31, 2018 4:06 am

All Mikrotik products that i have presents these issue... All starts working great but after a while, DHCP Server stop working. Since 6.3X I have this problem and I don't found any solution, just unplug and plug power cable... A simple tplink router does not have these problems and even a 16-core CCR does. Is incredible. A year waiting for solutions.
Mikrotik products have serious problems with DHCP: FIX THEM!
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Re: DHCP server problem

Wed Oct 31, 2018 4:19 am

does really dhcp stop working? Unless you have data from packet sniffer and log, you cant prove that it is mikrotik's fault and such blind blaming is ridiculous - I had never such issue on any of my routers. My ISP has CCRs and also don't have this problem. I am sure that there many other customers who never saw your issue. The issue must be related to your environment/setting.

If you got problem, you cant just say "mikrotik must fix it". You need to point out where exactly is the problem with logs and packet captures.
Van9018 gave you excellent guide so you can debug it and write good bug report. With good bug report, developers will understand where is issue and they can fix it. Without proper bug report, they cant fix it because they dont know where the issue is.
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Re: DHCP server problem

Thu Nov 01, 2018 11:43 am

I have lots of Mikrotik Routers on my network and that of my clients running DHCP server. I have not come across this issue for once. I think the issue must have to do with the specific network. Just like Van said, take more steps to troubleshoot and I'm sure you would see the problem somewhere.
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Re: DHCP server problem

Thu Dec 27, 2018 5:18 pm

We manage 6 mikrotik routers, different models and different RouterOS version, all version up 6.X, and with all of them got problem with DHCP, specially with leased IP address
-=< FErArg >=-
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Re: DHCP server problem

Mon Jan 06, 2020 9:10 am

same here, we have DHCP Problems!
I set up a Kids Control, that based on IP Adresses. But some times the wrong System get the wrong ip.
Happened on Fire TV Sticks (Cable not Wlan) and iMac!


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