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ELRP is unable to detect a loop when the looped packets are within QP8

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TitleELRP is unable to detect a loop when the looped packets are within QP8
Symptoms
ELRP is unable to detect a loop when the looped packets are within QP8.

* X430-48t.22 # show ports 12,13 utilization bandwidth
Port     Link    Link   Rx             Peak Rx       Tx            Peak Tx
         State   Speed  % bandwidth    % bandwidth   % bandwidth   % bandwidth
================================================================================
12        A       1000    100.00        100.00        100.00          100.00
13        A       1000    100.00        100.00        100.00          100.00
================================================================================
          > indicates Port Display Name truncated past 8 characters
          Link State: A-Active, R-Ready, NP-Port Not Present, L-Loopback

* X430-48t.27 # show ports 12,13 qosmonitor no-refresh
Port Qos Monitor
Port   QP1      QP2      QP3      QP4      QP5      QP6      QP7      QP8
       Pkt      Pkt      Pkt      Pkt      Pkt      Pkt      Pkt      Pkt
       Xmts     Xmts     Xmts     Xmts     Xmts     Xmts     Xmts     Xmts
===============================================================================
12     0        0        0        0        0        0        0        39576272
13     0        0        0        0        0        0        0        39525695

* X430-48t.28 # show elrp
ELRP Standalone Client:       Enabled

Number of ELRP sessions:          1
Number of ELRP pkts transmitted:  144
Number of ELRP pkts received:     0

                                                Pkts     Pkts            Disable
Client  Vlan        Ports  Int.    Count Cyclic Xmit     Rcvd     Action Port (sec)
--------------------------------------------------------------------------------
CLI     vl-100       All   1        0     Yes    144       0         L     15
--------------------------------------------------------------------------------
Action : (P) Print , (L) Log , (T) Trap , (C) Callback
Environment
  • EXOS
  • Summit X430
Cause
By default we use QP8 (highest CPU queue) while lifting the ELRP packets to CPU. As both the broadcast storm as well as ELRP packets are in the same queue, it is very much possible for the ELRP packets to get lost.
With the result that the loop is not being detected.
Resolution
The workaround/solution for this would be to avoid having user traffic within QP8, but only have control traffic within QP8.
In general it would be good to use rate limiting of unknown/broadcast data to limit the impact of a loop condition.
Additional notes

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