Cisco Nexus 9000 Series Configuration Manual page 90

Guidelines and Limitations for Switching Modes
Because it waits to forward the frame until the entire frame has been received and checked, the switching
speed in store-and-forward switching mode is slower than the switching speed in cut-through switching mode.
Guidelines and Limitations for Switching Modes
Consider the following guidelines and limitations for each of the switching modes:
Cut-Through Switching Mode Guidelines and Limitations
• show commands with the internal keyword are not supported.
• When an FCS error is discovered, FCS error packets are not immediately dropped. (The packet
• Packets with FCS errors are not mirrored if SPAN is configured.
• By default, all HiGig
• Beginning in 7.0(3)I1(2), cut-through switching is supported on the Cisco Nexus 9500 Series switch
• Cut-through switching is supported on Cisco Nexus 9300 Series switches for traffic from 40G ports
• The Cisco Nexus 31128PQ switch operates in over-subscribed mode only and therefore is unable to
Store-and-Forward Switching Mode Guidelines and Limitations
• show commands with the internal keyword are not supported.
• The store-and-forward switching mode is supported on Cisco Nexus 9300 Series switches, Cisco Nexus
• The store-and-forward switching mode is supported on the following devices:
Cisco Nexus 9000 Series NX-OS Layer 2 Switching Configuration Guide, Release 7.x
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transmission may have already been in progress.) For this situation, the packet is truncated and marked
with error marking in EOF. The packet is then dropped at the next node.
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links operate at 42G to compensate for the HiGig
support the full line rate of 40G from the front-panel ports. However, the speed mismatch could result
in packets being forwarded in store-and-forward mode. To make sure that the traffic is cut through, you
can use the switching-mode fabric-speed 40g command to change the HiGig
to operate at 40G and use the show switching-mode fabric-speed command to verify the configuration.
This feature is supported only for the Cisco Nexus 9500 Series switches with the 9636PQ line card. It
is not supported for the Cisco Nexus 9300 Series switches. Operating at 40G improves latency but
prevents the fabric from supporting the full line rate. See the Cisco Nexus 9000 Series NX-OS Layer 2
Configuration Guide for more information.
with the 9636PQ line card.
(ALE ASIC) to 10G ports (NFE ASIC). It is also supported for traffic between 10G ports (NFE ASIC)
to 10G ports (NFE ASIC) only when buffer-boot is not enabled. Traffic going from 10G ports (NFE
ASIC) to 40G (ALE ASIC) ports will always be store and forward.
support cut-through switching mode.
9500 Series switches, and Cisco Nexus 3164Q, 31128PQ, 3232C, and 3264Q switches.
◦ N9K-C9508-FM2
◦ N9K-X9432PQ
◦ N9K-X9536PQ
◦ N9K-X9632PC-QSFP100
Configuring Switching Modes
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header over fabric and to
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links on the 42G ports