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IdentiFi Wireless clients having intermittent DHCP issues - AP dropping DHCP offer packets

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TitleIdentiFi Wireless clients having intermittent DHCP issues - AP dropping DHCP offer packets
Symptoms
  • IdentiFi Wireless clients having intermittent DHCP issues - AP dropping DHCP offer packets
  • The AP Minimum basic rate can affect how many packets per second (PPS) the AP can process for wireless clients
Environment
  • IdentiFi Wireless
  • All software versions
  • Bonjour
Cause
Summary of the AP Minimum Basic Rate setting and how it can affect packet processing (based in management frame receival of multicast/broadcast packets including IPv6):
1. If Min Basic Rate = 6mbit, Max of 512pps can be processed
2. If Min Basic Rate = 12mbit, Max of 1024pps can be processed
3. If Min Basic Rate = 24mbit, Max of 2048pps can be processed
Resolution
  • If the topology being used is Bridged at AP (B@AP) take a real-capture remote trace as follows: How to use Real Capture to capture wireless and wired traces from an IdentiFi Access Point
  • If the topology is Bridged at Hardware Controller (B@HWC) you will want to setup a port mirror of the wireless controller and take a trace on a destination PC port.
  • In wireshark, click Statistics dropdown menu > IO Graph
  • This will show you the number of frames being seen in packets per second (default values set).
  • If seeing over 500pps of multicast/broadcast traffic, track down the source of the flooding.
  • Common issues seen can be a device or devices on the LAN flooding IPv6 Multicast Solicitation packets, so options are to either:
  • Block IPv6 on the switch ports.
  • Block IPv6 on the wireless Rules section (Ethertype = IPv6 with deny rule at top of the rules list).
  • Determine cause for source of flood on LAN segment and resolve (faulty PC NIC flooding traffic, network loop, network reflection, etc)
  • Verify under Wireless topologies under Multicast Filters you are only allowing necessary multicast groups, and not 0.0.0.0/0 (ALL) groups
  • Multicast Filters under the topology should not be set to allow all, be as specific as possible with your rules
  • If Topology is B@HWC, ensure Subnet Mask is matching on both DHCP Server and the layer-3 interface on the controller (if applicable)
Additional notes

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