Something that came up in the field, a ESXi host for some reason magically lost connection to our vCenter cluster. I checked the networking side and nothing came up (just connection down for the ports connecting to the host). I then KVMed into the server and the NICs looked like they were up as well! What? I couldnt ping or RDP to any vm on the host — what gives??
The decision from mgmt was to reboot the box. After rebooting the host, I was able to ping/RDP to the device and it came back into the vCenter. OK so what happened?

Generally I keep the SSH on the ESXi Firewall turned off for obvious security reasons. I went into ESXi to turn it on and I SSHed into the host.

login as: root
Using keyboard-interactive authentication.
The time and date of this login have been sent to the system logs.
VMware offers supported, powerful system administration tools.  Please see for details.
The ESXi Shell can be disabled by an administrative user. See the vSphere Security documentation for more information.

OK so now that I’m in, lets run a few commands….

~ # esxcfg-nics -l

Name    PCI           Driver      Link Speed     Duplex MAC Address       MTU    Description

vmnic0  0000:0b:00.00 bnx2        Up   1000Mbps  Full   34:40:b5:d4:4e:c4 1500   Broadcom Corporation Broadcom NetXtreme II BCM5709 1000Base-T

vmnic1  0000:0b:00.01 bnx2        Down 0Mbps     Half   34:40:b5:d4:4e:c6 1500   Broadcom Corporation Broadcom NetXtreme II BCM5709 1000Base-T

vmnic2  0000:10:00.00 bnx2        Down 0Mbps     Half   5c:f3:fc:9e:c7:d8 1500   Broadcom Corporation Broadcom NetXtreme II BCM5709 1000Base-T

vmnic3  0000:10:00.01 bnx2        Down 0Mbps     Half   5c:f3:fc:9e:c7:da 1500   Broadcom Corporation Broadcom NetXtreme II BCM5709 1000Base-T

vmnic4  0000:1a:00.00 be2net      Up   10000Mbps Full   00:00:c9:da:3a:62 1500   Emulex Corporation OneConnect 10Gb NIC

vmnic5  0000:1a:00.01 be2net      Up   10000Mbps Full   00:00:c9:da:3a:66 1500   Emulex Corporation OneConnect 10Gb NIC

vusb0   Pseudo        cdc_ether   Up   10Mbps    Half   36:40:b5:f9:3d:8f 1500   Unknown Unknown

This command list out the NICs I got on this host. It also tells me the name VMware gives it. In this case, we got I’m interested in 2 NICs on this host named vmnic4 and vmnic5. So to get more details on them run the following…

~ # ethtool -i vmnic4
driver: be2net
firmware-version: 4.2.433.3
bus-info: 0000:1a:00.0

~ # ethtool -i vmnic0
driver: bnx2
version: 2.0.15g.v50.11-7vmw
firmware-version: bc 7.4.0 NCSI 2.0.11
bus-info: 0000:0b:00.0

OK this gives me the driver version and the firmware version. Why is this information important for this post? After the VMware Admin went through the logs and found nothing showing why the host lost networking connectivity, and after I looked on my end and nothing looked out of the ordinary, we called up VMware Support and sure — a BUG with this version. The fix was to upgrade this code to a newer code and as of one week (when we did it), so far so good!

William Zambrano

William Zambrano

NYC networkers is run by William Zambrano, a passionate network engineer who has been in the IT industry for eight years who posts up blog articles, YouTube videos, and holds events in the NYC area. He lives in Queens, New York and has consulted in various different companies in the NY area. Previously William worked as a Cisco Certified Systems Instructor (CCSI) but now currently works for Arista Networks serving as a Systems Engineer. William can be reached by email at

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