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What happens when an Extreme switch receives an LACP PDU of size greater than the IEEE recommended size of 128 bytes?

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TitleWhat happens when an Extreme switch receives an LACP PDU of size greater than the IEEE recommended size of 128 bytes?
Question
What happens when an Extreme switch receives an LACP PDU of size greater than the IEEE recommended size of 128 bytes?
Environment
  • Summit
  • Blackdiamond
  • EXOS
  • 3rd party vendor switch (eg: HP)

 
Answer
  • Please check the output of 'show log' and you will find messages related to the reception of such 'invalid' PDUs. 
07/27/2017 04:42:31.14 <Erro:LACP.RxPDUSizExcd> Slot-1: Received PDU LACP size exceeded. Incoming Port: 2:54 PDU size: 132 required size: 128 
  • The output of 'show lacp counters' confirms the rejection of these invalid PDUs
# show lacp counters
 
LACP PDUs dropped on non-LACP ports : 11959
LACP Bulk checkpointed msgs sent    : 0  
LACP Bulk checkpointed msgs recv    : 0  
LACP PDUs checkpointed sent         : 0  
LACP PDUs checkpointed recv         : 0  
 
Lag        Member     Rx       Rx Drop  Rx Drop  Rx Drop  Tx       Tx     
Group      Port       Ok       PDU Err  Not Up   Same MAC Sent Ok  Xmit Err
--------------------------------------------------------------------------------
53         53         0        0        0        0        0        0       
           54         0        1948     0        0        1882     0       
 

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  • A tcpdump from the Extreme switch confirms the same. 
User-added image
  • As per the IEEE recommendations of 802.3ad the maximum size of an LACP PDU is only 128 bytes. 
  • Therefore, this is expected behavior as per design and cannot be altered. 
  • Request the customer to check with the 3rd party vendor switch on why they are sending LACP PDUs of size greater than 128 bytes. 

 
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