Solved: Re: Catalyst 9k Switching Modes ( Cut-Through vs Store-and-Forward)

chira.cipri@gmail.com · ‎08-01-2021

Hello community,

What is the default switching mode on the Catalyst 9K series of switches ? Store-and-forward or Cut-through ? Can the switching mode be changed from the configuration ?

I have searched through Cisco docs and I can't find anything on the Cat 9Ks. I can only find information about the Nexus line of switches, and it seems a lot of them support cut-through switching, which is even the default switching mode at least for the Nexus 3Ks and Nexus 9Ks.

https://www.cisco.com/c/en/us/td/docs/switches/datacenter/nexus9000/sw/7-x/layer2/configuration/guide/b_Cisco_Nexus_9000_Series_NX-OS_Layer_2_Switching_Configuration_Guide_7x/Configuring_Switching_Modes.html

https://www.cisco.com/c/en/us/td/docs/switches/datacenter/nexus3000/sw/layer2/503_U3_1/b_Cisco_n3k_Layer_2_Switching_Config_503_U31/b_Cisco_n3k_Layer_2_Switching_Config_503_U31_chapter_01000.html

Scott Hodgdon · ‎08-03-2021

chira.cipri@gmail.com ,

Catalyst 9K platforms use only Store-and-Forward. You can see this in the packet walk slides of the Cat 9K architecture sessions on ciscolive.com. Go to the on-demand library and search for:

Catalyst 9000 Series Access Switching Architecture - BRKARC-3863 (Barcelona 2020), Minhaj Uddin Presenter
https://www.ciscolive.com/c/dam/r/ciscolive/emea/docs/2020/pdf/BRKARC-3863.pdf (if you can go directly there)

Slide 66 has the Unicast packet walk and shows the packet being buffered while the UADP ASIC operations take place. All Cat 9K have UADP ASICs, and so they all use this same mechanism.

Cheers,
Scott Hodgdon

Senior Technical Marketing Engineer

Enterprise Networking and Cloud Group

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