I have a mellanox sn2700 switch with qsfp28 100g ports and meet to connect a router for DHCP and internet that only has rj45 ports.

Is there a way to connect the two via an adapter/cable?


I am eyeballing the following two adapters and wonder whether anyone ever got this to work:




You'll need an interim device. A QSFP28 port can generally be broken out into four 10G interfaces (there are multiple ways of doing this, you'll need to find one that works with both of the devices).

You would need to a device that accepts a 10G QSFP+ that can also accept a RJ45 that also runs at the speed of your router. For example, not all QSFP+ ports can run at 100Mbps or lower - some can only do 10G or 1G.

There are 10G switches that have both QSFP+ and 10GBASE-T support, although you may need to insert a regular 1000BASE-T GBIC. Without knowing more about your router it's hard to say.

Based on the information in the comments, a small device like a Mikrotik CRS305-1G-4S+IN would suffice:

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Get a 10G breakout cable for your QSFP28 interface and compatible optics for the Mikrotik, then plug your router into the gigabit ethernet interface (or keep that for a management network and throw a regular 1Gb GBIC into one of the SFP+ ports)

  • Just to clarify did you mean you have never seen a SFP+ device that can be plugged into QSFP28 ports? Cause QSFP generally works with QSFP28 ports on most switches. Or is "QSFP+" a synonym for "SFP+"? – Matt Mar 6 at 10:31
  • I have a Cisco RV325 router with RJ45 1Gb ports, and my Mellanox SN2700 has 16 QSFP28 ports. – Matt Mar 6 at 10:34
  • Uh I'm not entirely sure what I meant when I wrote that line to be honest. I think I meant I've never seen a QSFP28 device that will accept a base-t connection. I'm just going to delete it because you're right it doesn't make sense – Mark Henderson Mar 6 at 10:40
  • You're going to need another device sitting between your switches then. It can be something basic. I'll update my answer with a suggestion. – Mark Henderson Mar 6 at 10:41
  • I wonder whether the following might also work: 1Gb GBIC into a QSA and that into the switch. store.mellanox.com/products/…. I am asking because your suggestion still requires a QSA adapter to connect SFP+ to QSFP+ or, as you suggested, breakout cables. I wonder how this is better than 2 adapters (please see edit of my question). – Matt Mar 12 at 4:30

I actually found a better answer to what @Mark Henderson suggested. I received the QSA adapter and GBIT adapter and both in combination allow for a RJ45 1Gbit connector to be plugged into a QSFP28 port on my Mellanox Switch. Here are the components I got which are confirmed to work with the Mellanox SN2700 and HPE SN2700M switches. Total Cost: Around USD 25 (I bought both adapters new on Taobao.com)

Components needed:

  • 10Gtek for Cisco GLC-T/SFP-GE-T Gigabit RJ45 Copper SFP Transceiver Module, 1000Base-T
  • Mellanox Network Adapter, SFP+ to QSFP (MAM1Q00A-QSA)

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