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Will ELRP packets be discarded in case mcast flood rate-limit enabled and threshold exceeded?

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TitleWill ELRP packets be discarded in case mcast flood rate-limit enabled and threshold exceeded?
Question
Will ELRP packets be discarded in case mcast flood rate-limit enabled and threshold exceeded?
Environment
  • all EXOS platforms
  • ELRP
  • multicast flood rate-limit
Answer
Locally generated ELRP packets will not be discarded. Transit ELRP packets will be treated as regular multicast packets.

It can be demonstrated using following topolgy:
[port3]SW1[port2]——[port2]SW2[port1]
      \——[port3]SW3[port1]——/


When create 300 VLANs and enable ELRP in each of them, switch will generate 1 ELRP packet per second per VLAN to detect loop in each of them (by default configuration):
SW1.1 # show ports 2,3 utilization packets
Port     Link    Rx              Peak Rx          Tx               Peak Tx
         State   pkts/sec        pkts/sec         pkts/sec         pkts/sec
================================================================================
2         A           311            311              311             311
3         A           312            312              312             312
================================================================================
          > indicates Port Display Name truncated past 8 characters
          Link State: A-Active, R-Ready, NP-Port Not Present, L-Loopback

ELRP packets generated locally don’t being dropped by mcast flood rate-limiter:
SW1.2 # show configuration | i flood
configure port 2 rate-limit flood multicast 100
configure port 3 rate-limit flood multicast 100
SW1.3 # show ports 2,3 utilization packets
Port     Link    Rx              Peak Rx          Tx               Peak Tx
         State   pkts/sec        pkts/sec         pkts/sec         pkts/sec
================================================================================
2         A           317            317              317             317
3         A           317            317              317             317
================================================================================
          > indicates Port Display Name truncated past 8 characters
          Link State: A-Active, R-Ready, NP-Port Not Present, L-Loopback
SW1.4 # show ports 2,3 rate-limit flood no-refresh
Port Rate-Limit Discard Monitor
Port      Link        Rx Pkt      Rx Byte       Rx Pkt       Rx Pkt   Flood Rate
          State        Count        Count        Bcast        Mcast     Exceeded
================================================================================
2         A           711379     49802534            0       711379            0
3         A           711379     49802534            0       711379            0
================================================================================
          > indicates Port Display Name truncated past 8 characters
          Link State: A-Active, R-Ready, NP-Port Not Present L-Loopback

If we enable mcast flood rate-limit on SW2 or SW3 we will see that transit ELRP packets will be dropped if rate-limit exceeded:
SW2.1 # show configuration | i flood
configure port 1 rate-limit flood multicast 100
configure port 2 rate-limit flood multicast 100
SW2.2 # show ports 1,2 rate-limit flood no-refresh
Port Rate-Limit Discard Monitor
Port      Link        Rx Pkt      Rx Byte       Rx Pkt       Rx Pkt   Flood Rate
          State        Count        Count        Bcast        Mcast     Exceeded
================================================================================
1         A          2529474    177421592            0      2529057        53579
2         A          2156357    151268524            0      2155971        56278
================================================================================
          > indicates Port Display Name truncated past 8 characters
          Link State: A-Active, R-Ready, NP-Port Not Present L-Loopback
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