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My servers are currently have 25Gbps NIC, but switch ( Cisco Nexus 9300 series) has only 400Gbps.

I would like to be able to break out the 400Gbps connection into four 25Gbps connections. Is this possible? If not, what are my other options?

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  • What Nexus 9300 switch supports 400G?
    – Zac67
    May 24, 2023 at 15:02
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    The 9300 GX and 9300 GX2 models do. May 24, 2023 at 15:55

2 Answers 2

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Yes

According to this page, each port of the Nexus 9300 is breakout capable.

You can configure the interface with the interface breakout module command.

Of course you will need the ad-hoc cable.

It is not obvious from this page from Cisco that you can goes from 400G to 25G (only 400 -> 100 is listed), however, in this guide in scenario 7 and 8, the 400G to 25G options are cited:

enter image description here

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    Just FYI, this solution is not a direct breakout cable and requires additional components (i.e. #2 is an MTP cartridge). If OP needs direct breakout from 400G to 25G, it's standardized as IEEE802.3bs (400GBASE-SR16). Sadly no network vendors support it (yet) and no transceiver vendors sell it (yet). May 24, 2023 at 20:39
  • @JordanHead thanks for the info. I routinely do 100->4x25 but doesn't work with 400G yet.
    – JFL
    May 25, 2023 at 6:50
  • Right, I meant if the interface is strictly 400G vs a multirate one that you can set at 100 and break out from there without additional stuff (i.e. just a breakout cable). May 25, 2023 at 11:27
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That's possible.

Assuming an N9K-C9316D-GX, 9364D-GX2A, 9348D-GX2A, or 9332D-GX2B:

Breakout supported on all ports, 1-16: 2x200, 4x100, 2x100, 8x50, 4x50, 2x50, 4x25, 4x10

https://www.cisco.com/c/en/us/products/collateral/switches/nexus-9000-series-switches/nexus-9300-gx-series-switches-ds.html

https://www.cisco.com/c/en/us/products/collateral/switches/nexus-9000-series-switches/datasheet-c78-743854.html

According to the Breakout Cable Ordering Guide, for instance a QSFP-100G-SR4-S should be able to connect to 25GBASE-SR modules on the server side, using an appropriate optical breakout cable or harness (MPO12↔4x2xLC MMF).

Using a DAC breakout could also be possible but might cause compatibility options with your server NICs. I'd stick to fiber.

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