Arista 7500 Series router

For a transceiver to transmit traffic, it has to linkup on a switch. Even before that it has to be recognized by the switch.

I found several transceivers that work on one switch("port up" recognized) but not another switch("port down" not recognized). My understanding is that this recognition step of switch queries each transceiver for info using I2C. But what info?

How would I know more if a transceiver was not recognized, and for what reason? The transceiver certainly satisfies the transceiver MSA compliance.

Is there a config or setting file in the switch or online that have the checklist, or is this hard-coded? I want to know exactly how does the switch ask for transceiver.

I heard some Arista switch that rejects anything foreign, how would I be sure?

2 Answers 2


SFP transceivers have a small EEPROM that can be checked for the expected branding. Many devices only support transceivers with the same brand. It can be easily forged, you can buy "XYZ-compatible" transceivers everywhere.


For transceivers to link up you need a few things. The "port down" or not having the port light up does not necessarily mean the optic is not compatible.

First, transceiver needs to be compatible with the switch. This means compatible hardware and the vendor you purchased these from coded these correctly. Arista is an easy one to code so finding a 3rd party for this system is easy.

Second, Both transceivers MUST be the same wavelength (850nm, 1310nm, or 1550nm) and the same speed (1G, 10G, or 40g).

And last, your ports must be configured correctly and enabled. Not all switches are plug and play, some require initial setup and/or provisioning when an optic is installed.

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