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S-Series Printing HostDOS messages with C-tag Repeating in Logging Buffer After Connecting EXOS Switch

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TitleS-Series Printing HostDOS messages with C-tag Repeating in Logging Buffer After Connecting EXOS Switch
Symptoms
  • Connecte  Summit
  • Intermitttent traffic loss
    • S-Series logs error
<165>Feb 23 18:22:53 203.0.113.1 Last message repeated 21 times
<165>Feb 23 18:22:53 203.0.113.1 HostDoS[1] Attack ( arpNd ) detected on vlan.0.34 
[ InPort(ge.1.19) LEN(68) DA(FF:FF:FF:FF:FF:FF) SA(00:CA:FE:24:12:52) C-TAG(8100:0022) ETYPESummit(0806) ]


 
Environment
  • S-Series
  • Summit
  • IP Phones
Cause
Network loop originating from an edge switch can trigger messages of type "HostDoS[1] Attack ( arpNd )" on the S-Series. 
The message could be an indication of a possible loop originated in an edge switch (i.e. Summit switch). For example, if an IP Phone that has two Ethernet interfaces have both interfaces connected to the same Summit switch, since spanning tree is not configured/enabled by default on the switch, the 'double' connectivity will cause a loop in the network. and the S-Series will interpret such event as a HostDos Attack.
Resolution
Locate the source from where the messages are coming from and do the following: 
  1. Disconnect any redundant link connected to the target switch.
  2. Configure spanning tree on the summit switch as to prevent future problems.
Additional notes

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