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High switch CPU utilization due to Windows 10 Clients generating excessive mDNS traffic

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TitleHigh switch CPU utilization due to Windows 10 Clients generating excessive mDNS traffic
Symptoms
  • Switch CLI is slow and unresponsive
  • Excessive mDNS multicast traffic flooded on the network
  • High switch CPU utilization of bcmRX process
  • Multicast traffic slow pathed to CPU
  • Table full messages in switch log
Environment
  • Summit
  • BlackDiamond
  • EXOS
  • Windows 10
Cause
A software defect in Windows 10 causes clients to incorrectly respond to all mDNS requests in the network. This results in excessive multicast traffic being flooded onto the network and can lead to table full conditions in EXOS switches.

More information on this behavior can be found here:
https://social.technet.microsoft.com/Forums/en-US/b334e797-ef80-4525-b74a-b4830420a14e/windows-10-spams-network-with-invalid-mdns-response-packets?forum=win10itpronetworking

 
Resolution
Resolution

Consult with Microsoft to upgrade the Windows 10 clients to a version containing the software fix. 

Workaround

The following changes can be made to help reduce CPU utilization and free up table space:

configure forwarding ipmc lookup-key group-vlan
configure forwarding ipmc local-network-range fast-path


It may also be desirable to block the mDNS traffic until the Windows 10 fix can be implemented.  An ACL can be applied to the affected ports/VLANs to block any unnecessary mDNS traffic.

ACL rule examples that block and count mDNS are provided below:

entry block_IPv4mDNS{
if match all {
destination-address 224.0.0.251/32 ;
}
then {
deny;
count ipv4mDNSdeny ;
}
}

entry block_IPv6mDNS{
if match all {
destination-address ff02::fb/128 ;
}
then {
deny;
count ipv6mDNSdeny ;
}
}
Additional notes

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