Cisco 2K FEX 40/100 BiDi

The question comes up often about using the Cisco 40/100G BiDi QSFP28 optic for use with the Cisco Nexus 2348UPQ, or even other current Nexus 2300 FEX modules, instead of using the older 40G BiDi QSFP optic.

The quick answer is, no. The 40/100G BiDi optic is based on the QSFP28 standard and all the Cisco Nexus 2300 FEX QSFP up-link ports are based on the older QSFP standard. Since the 40G BiDi has a long lead time as of this writing, the best alternative option are Active Optical Cables (AOC).

Find number of ports by type

One common issue, and question, I get in the field is determining how many of a particular port type and speed is deployed in your data center network? This post will provide you a quick little command you can run on your Cisco Nexus switches, which outputs the interface and the type in a single line. You can manipulate manually, or export to a text file and send somewhere else for import into Excel:

show interface capabilities | section Ethernet | egrep ^Ethernet|^\s+Type | awk 'NR%2{printf "%s ", $0;next;}1'

A note for those using Nexus 7K and/or 5K infrastructure, you may run into issues with awk, so for now, this would work for you, just not as clean:

show interface capabilities | section Ethernet | egrep Ethernet|Type

Reset ESXi evaluation license

A quick and simple way to reset the evaluation license, never to be done to avoid properly licensing either is to SSH into the ESXi host and execute the following command:

rm -r /etc/vmware/license.cfg && cp /etc/vmware/.#license.cfg /etc/vmware/license.cfg && /etc/init.d/vpxa restart

No gateway or traffic reachability with Nexus FEX and Nexus 9000

If you have deployed a FEX with a Cisco Nexus 9K switch, either the 23XX or an integrated FEX within a chassis, and you’re unable to reach the gateway and/or having general traffic issues, you need to look at your FEX configuration on your Cisco Nexus 9000 series switch. For those who’re familiar with deploying FEX with Cisco Nexus 5000 series switches it can be possible to get the configuration incorrect if you follow the method of deploying a FEX as you’ve always done. Here below is the basic configuration for getting a FEX up and running:

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Virtualbox Linux guest DNS problems Anyconnect

If you’re running a Linux guest in Virutalbox with a Windows host and you’re using AnyConnect, primarily connected to a VPN, you may experience issues with DNS resolution in your Linux guest, generally in NAT mode. The fix isn’t very obvious up front but isn’t too hard to fix. Below is how to use the VBoxManage.exe tool to setup a “DNS Proxy” on the Windows host for your Linux guest; thus, your DNS resolution will come from the Windows host itself.


cd c:\Program Files\Oracle\Virtualbox
VBoxManage.exe modifyvm "your_Linux_VM_guest_name_here" --natdnshostresolver1 on

Note: You still need to keep the double quotes around your guest name.

No matching key exchange method found – Linux and Mac OSX

Lots of people get this error because most OS developers are deprecating the use of insecure key exchanges; however, there are many equipment and other OS vendors which still require use of this. This modification is for permanent resolution of the matter, may not be the most “hardened” manner, but solves your problems moving forward.

I have a YouTube video that’ll help guide you through this:

Nexus 93180YC-EX with Cisco Nexus 2348UPQ 40GbE

I  have seen this around the Internet and a lot of the information is old, and incorrect at the date of this blog post. Thus, what I will link here is the official support matrix Cisco provides for the Cisco Nexus 9000 series switches and the support Cisco Nexus FEX models. One thing to note, if you hover over the “YES” in the cell you choose, it will provide you with the supported connectivity options.

Now, to answer the question above, yes, you can connect the Cisco Nexus 2348UPQ to the Cisco Nexus 93180YC-EX using 40GbE from the FEX uplink ports to the 40GbE ports on the 93180YC-EX. If you are reading the guidelines and limitations where it states something like this “FEX is not supported on 40GbE ALE uplinks” then you need to understand the Cisco Nexus 93180YC-EX does not use the older generation ALE, instead it uses the newer, 2nd generation, Cloud Scale ASIC LSE (Leaf-and-Spine Engine); thus, this limitation does not apply.