Posted on September 14, 2020 7:36 am
 |  Asked by mah m
 |  27 views
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I am new to this MXP/MTP cabling. I understand that, this will break down 100GbE MXP ports to (3) 40GbE QSFP ports or 100GbE to (12) 10GbE ports.

I am referring to the below documentation and understand it has 12 pairs but, How come 100GbE on one side and split into 120GbE ?

https://www.arista.com/en/um-eos/eos-section-11-3-ethernet-physical-layer?searchword=mxp

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Answered on September 14, 2020 7:37 am

Hi Mahesh,

Thanks for reaching out.

Among 12 split ports first port(1) and last port(12) are not used.
So 2-11 ports will be active => 10 lanes *10G = 100 Gb.

Thanks,
Bhavana.

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Posted by Adam Levin
Answered on September 14, 2020 9:49 pm

Hello Mahesh,

To be clear about the previous answer, the MTP24 cable has 12 pairs (24 fibers), so if you breakout into 10G, you get all 12 pairs and can use 12 x 10G ports.  When you use it as a 100G port though, two of the pairs are not used.  This is due to how the hardware is designed and the fact that the standard high speed port is 100G, not defined as 120G (though it could have been).  Just a weird quirk of the standards.

So, you get either 1 x 100G, or you can break out to 3 x 40G or 12 x 10G using the same port with the proper breakout cables.  If you use the 12 x 10G breakout, you get those 12 ports on the transmit side even though it's a single 100G port, and all 12 ports can run at a full 10G.  It will look in the config like you have 12 ports, and they will be numbered with a slash.  So if port 40 is a 100G port, and you set it for 12 x 10G, you will get 40/1, 40/2, 40/3 etc up to 40/12.

I hope this answers your question.  Please let us know if you have additional questions.

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Posted by smunro
Answered on September 15, 2020 2:01 pm

HI Mahesh,

I just wanted to clarify for other readers that didn't check the link, that the breakout on 100G MXP/MTP Ports to 12x10G is only capable on certain devices where embedded optics are present within the switch (and not individually  field replaceable ) and shouldn't be confused with the QSFP 100G Optics.  The two platforms we had were the 7280SE-72 fixed form factor switch and the 7500E-12CM line card for the 7500E Chassis, both of which will be End of Life (EOL) in June of 2021, see the notices below:

DCS-7280SE-72

https://www.arista.com/en/support/advisories-notices/end-of-sale/3765-end-of-sale-of-7280se-series

DCS-7500E-12CM-LC

https://www.arista.com/en/support/advisories-notices/end-of-sale/3764-end-of-sale-of-7500e-series-linecard

There was also the CFP2 optic that was compatible with the DCS-7500E-6C2 line card, which used the 100G-SR10 format allowing you to break out to 10x10G.

One key point here is that the technology was based on 10G per channel or fiber pair, the newer format 100G QSFP optics such as the 100GBASE-SR4 or 100GBASE-PSM are based on 25G per channel and can be broken out to 4 x 25G.

I hope this helps.

Thanks

Stuart

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