Why the first packet is discarded after the Mac-Limit is configured for the S2700 port


After the Mac-Limit is configured for the S2700 port, the first packet learned by each MAC address is sent to the CPU for software learning. If the Mac-Limit is not configured, the hardware directly forwards the first packet, and this problem does not occur.

When the first packet is sent for software learning, the hardware also forwards the first packet for the S3700 or S5700 switch but not for the S2700 switch due to limitations of the S2700 switch.

After the Mac-Limit is configured, the first packet is discarded. However, after the MAC address is learned, the first packet is not discarded.

Other related questions:
What are the limitations for configuring VLAN mapping on the S2700
A maximum of 16 VLANs can be mapped on an interface. The C-VLAN ID must be different from the value obtained through the modulo operation against 128 on the VLAN allowed by the interface (VLAN ID mod 128); otherwise, a conflict occurs. For example, if the interface allows VLAN 130 to pass, the result of VLAN ID mod 128 is 2. In this case, the C-VLAN ID cannot be set to 2. The S2700SI does not support VLAN mapping.

What causes packet loss on the port of S series switches
For S series switches (except the S1700), packets will be discarded if traffic is too heavy or burst traffic occurs.

Why are a large number of packets discarded on an inbound interface of an S series modular switch
S9300 series switches running V100R001 and V100R002 send protocol packets to the CPU for processing and discard the packets at the hardware layer. The number of these discarded protocol packets is counted on inbound interfaces, which does not comply with RFC 2863. For switches running V100R002, patches in V100R002SPH009 and later versions can be installed to fix this problem. According to RFC 2863 and industry norms, only packets discarded due to buffer overflows is counted as discarded packets.

Reason for ping packet loss on S series switch
For S series modular switches: Ping packets sent from other devices to a switch are processed by the switch as fib-hit packets. The switch sends fib-hit packets to the CPU at the default CAR value to protect the CPU from being attacked by these packets. If the rate of ping packets sent to the CPU exceeds the CAR value, the switch discards the excess packets. To resolve the problem, set a larger CAR value for fib-hit packets.

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