On Junos QFX5120-48YM platforms, auto-negotiation is not enabled for 10ge-type transceivers. Resulting in the port remaining down when connected to a peer device with 1G/10G.

On Junos QFX5120-48YM platforms, due to quad port limitations, need to have the four adjacent ports running at the same speed as the clock is fed from the same source.

The SFP-10G can only have 10G speed on the switch side; it will auto-negotiate at 1g on the line side, but it cannot do AN (auto-negotiation) on the switch side and will always run at 10G XFI (SFI). This means that any 1G transceiver inserted in the shared quad port could remain down on default 10G speed. Similarly, by configuring 1G speed on the quad port, all the ports will be set to 1G, and the 10GE-T SFP could go down. Because of this ambiguity and due to the limitations described above, it is best to avoid SFPs of different speeds on the same quad port.

The 10GE-T can work at both 1G and 10G on the line side. This applies to 25G transceivers as well.

Workaround: For 1G and 10G connections, use 10GE-T type transceivers and avoid configuring speed on the Quad-port, this will ensure that the 10GE-T auto-negotiates properly with the peer regardless of 1G/10G speed. All ports need to be running at the same speed. It is best not to mix and match Optics

Resolved-In

junos:23.2R2-S4 junos:23.4R2-S4 junos:24.2R2-S1 junos:24.4R2

https://prsearch.juniper.net/problemreport/PR1855279