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DHCP server sending DHCPNAK packets

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TitleDHCP server sending DHCPNAK packets
Symptoms
  • Devices are not getting IP addresses from DHCP server
  • If you configure IP addresses statically, devices can browse internal and external resources with no issues.
  • Packet capture shows DHCP Requests make it to the server, however, the DHCP server responds with a DHCP NAK instead of a DHCP ACK
Environment
  • EXOS ALL
  • EOS
  • Bootprelay
  • DHCP
Cause
DHCP NAKs are usually sent due to the receipt of two DHCP request packets from the same DHCP client. Once the server receive two DHCP requests, it responds to one and NAK (deny) the other. 
Resolution
  • Ensure the port where the DHCP server is connected is only configured for the VLAN the server is part of. Remove all other VLANs from that server port. 
  • Ensure there are no Loops across VLANs. Since some DHCP packets are broadcast, packets will be flooded to all ports. Some of those ports might be erroneously connected to other VLANs (directly or indirectly, via a hub or another switch).
Additional notes

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