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How to force 1G speed for Juniper QFX5100 10G ports?

jp flag

I have available a Juniper QFX5100-48S switch (48 SFP 10G ports, 6 QSFP ports) that I cannot join into our network since an SFP DAC 10G cable connecting it to an SFP port on a HP V1810-48G switch does not work (the web panel on the HP switch says that on the connected port the link is down). The very same cable successfully negotiates a connection between the HP switch and a server with a 10G Ethernet port once the server port is forced via OS to 1G so my idea was to somehow force the SFP port on the QFX5100 to 1G speed (unsetting the auto-negotiation on the HP switch for the SFP ports is not allowed from the web panel).

The only instructions I could find to do that (here) on the Juniper switch state that, once logged in the management console and entered the CLI context, then configure, then edit interface, there should be possible to issue set xe-0/0/0 speed 1g to force 1G negotiation for the 10G port 0, which I cannot - there is not any speed subcommand available.

Can someone tell me what I am doing wrong or it is simply not possible?

Score:0
ru flag

DACs use 10G SFP+ modules which are not compatible with the V1810's SFP ports. In theory, they could work between SFP ports when the switch ignores the SFP+ properties - but a 10G port tries to link using 10GBASE-R which cannot work. SFP ports use 1000BASE-X.

The proper syntax for forcing a QFX's port speed to gigabit is link-speed 1g, see https://www.juniper.net/documentation/us/en/software/junos/interfaces-ethernet-switches/topics/ref/statement/link-speed-interfaces-qfx-series.html

If that doesn't work you should use a fiber link, e.g. with 1000BASE-SX modules for multi-mode fiber.

Francesco avatar
jp flag
Thank you for your help; I had already tried the `link-speed 1g` statement, which needs to be applied to an aggregated interface *aeX*, not a plain one). I managed to create an aggregated interface; unfortunately, setting the `link-speed 1g` does not work with either *ge/0/0/X* or *xe/0/0X* interfaces - the former just stays in unconnected state, the latter refuses the command saying that the underlying interface is not compatible with the requested speed. The only way I could make this work was with some old 1GBE optical transceivers on the QFX5100 and some spare optical fiber cabling.
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