TravelingPacket – A blog of network musings

Recently have been working with the S4128 switches. These have been great, and the price point is amazing.

The device comes with 2 ports that can be 10/40/or 100 Gig interfaces (given media). I needed to connect the port via a 40 gig DAC to a Dell server. When I plugged this in, a “show interface eth 1/1/26” would show the interface up, show the DAC model number and then would say “Protocol down”. I thought at first this could be mismatching vlans, etc. But after a few minutes found it had to be a negotiation issue.

After some checking I found this in the config:

interface breakout 1/1/25 map 100g-1x
interface breakout 1/1/26 map 100g-1x

Interface 1/1/26 is my connection to the server. After some digging with Dell we have to modify this. I ran the following command:

interface breakout 1/1/26 map 40g-1x

After running that command a sub-interface showed up. A “Show interface status” presents the following Eth 1/1/26:1. After configuring the sub interface as needed all seemed to work great.

I will post images of interface status later.