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End devices connecting to ExtremeWireless networks are receiving and accepting unwanted DHCP server offers

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Information

 
TitleEnd devices connecting to ExtremeWireless networks are receiving and accepting unwanted DHCP server offers
Symptoms
  • End devices connecting to ExtremeWireless networks are receiving and accepting unwanted DHCP server offers.
  • Client devices cannot access the network due to a non-network DHCP IP address.
Environment
  • ExtremeWireless appliances
  • All ExtremeWireless Access Points
  • firmware 10.31.05.0003
Cause
Valid end users, either wired or wireless, have enabled a DHCP server scope and are offering IP addresses to other end client devices, most times the DHCP scope is not within the valid network IP scope/range.
Resolution
The following set of rules have been successfully tested:

User-added image

Five rules in the Policy:

  • First is only to deny all IPv6 traffic.
  • Second rule allows traffic from the client (MU) into the AP, basically allows the initial DHCP Discover.
  • Third rule is to allow the network DHCP server IP traffic from the wired network to the clients.
  • Fourth rule blocks all DHCP Server traffic (destination) from all clients to a DHCP offer.
  • Fifth rule is for DNS traffic.

 

To fully test:

  • Place a second DHCP server on the network. Although the second DHCP server replied to the Discovers, the client only accepted the DHCP offer from the true network server.
  • Remove the second and third rules, and confirm the test clients do NOT receive an IP address when trying to connect to the test BSSID.
Additional notes
There may be other ways to block unwanted DHCP server traffic from end users or non-network devices, but the method tested here was designed for the Wireless Access Point and the first line of client traffic entering the network.

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