We were troubleshooting an issue with the N1K, where random VMs would lose network connectivity. Upon running a “show mod” on the N1K we saw the following:

switch# show mod | no-more
Mod Ports Module-Type Model Status
--- ----- -------------------------------- ------------------ ------------
1 0 Virtual Supervisor Module Nexus1000V active *
3 248 Virtual Ethernet Module NA licensed
4 248 Virtual Ethernet Module NA licensed
5 248 Virtual Ethernet Module NA licensed

Mod Sw Hw
--- ---------------- ------------------------------------------------
1 4.2(1)SV1(4b) 0.0
3 4.2(1)SV1(4b) VMware ESXi 4.1.0 Releasebuild-348481 (2.0)
4 4.2(1)SV1(4b) VMware ESXi 4.1.0 Releasebuild-348481 (2.0)
5 4.2(1)SV1(4b) VMware ESXi 4.1.0 Releasebuild-348481 (2.0)

Mod MAC-Address(es) Serial-Num
--- -------------------------------------- ----------
1 00-19-07-6c-5a-a8 to 00-19-07-6c-62-a8 NA
3 02-00-0c-00-03-00 to 02-00-0c-00-03-80 NA
4 02-00-0c-00-04-00 to 02-00-0c-00-04-80 NA
5 02-00-0c-00-05-00 to 02-00-0c-00-05-80 NA

Mod Server-IP Server-UUID Server-Name
--- --------------- ------------------------------------ --------------------
1 192.168.1.139 NA NA
3 192.168.1.134 00000000-0000-0000-0000-000000000000 localhost1.
4 192.168.1.136 00000000-0000-0000-0000-000000000000 localhost2.
5 192.168.1.137 42343a8f-65b9-e0ae-acf2-b6d4e3995147 localhost3.

Two of the VEM modules were showing up with the UUID value of all zeros. Running ‘vemcmd show card’ on the working host we saw the following:

~ # vemcmd show card | grep UUID
Card UUID type 2: 42343a8f-65b9-e0ae-acf2-b6d4e3995147

On one of the two non-working hosts, we saw the following:

~ # vemcmd show card | grep UUID
Card UUID type 2: 00000000-0000-0000-0000-000000000000

I then ran across this cisco forums page. And from that page:

startDpa calls a script in /opt/cisco/vXXX/nexus/vem-vXXX/shell/vssnet-functions and extracts the UUID from the ESXi host:

setBiosUuid() { local UUID UUID=$(esxcfg-info -u | awk ‘{print tolower($1)}’) if [ “${UUID}” != “” ] ; then doCommand ${VEMCMD} card uuid vmware ${UUID} fi }

So the UUID is obtained from “esxcfg-info -u”. Running that command on working and non-working hosts, I saw the following:

~ # esxcfg-info -u
42343A8F-65B9-E0AE-ACF2-B6D4E3995147

and from one of the non-working host:

~ # esxcfg-info -u
00000000-0000-0000-0000-000000000000

Looking over VMware KB 1006250, we see the following:

The UUID is read by the ESX host from the SMBIOS … … This UUID is not generated by VMware. It is unique to the hardware and is set in the BIOS by the vendor. The output of the dmidecode command may show other examples of missing data.

We were using ESXi and no ‘dmidecode’ utility is available. However we can use ‘vsish’ and ‘vim-cmd’ to query the same information. Here is output for a good host:

~ # vsish -e cat /hardware/bios/dmiInfo | head -5
System Information (type1) {
Product Name:R250-2480805W
Vendor Name:Cisco Systems Inc
Serial Number:FCH1551v06J
UUID:[0]: 0x42

and here is the vim-cmd results:

~ # vim-cmd hostsvc/hosthardware | grep uuid -B 6
(vim.host.HardwareInfo) {
dynamicType = ,
systemInfo = (vim.host.SystemInfo) {
dynamicType = ,
vendor = "Cisco Systems Inc",
model = "R250-2480805W",
uuid = "42343a8f-65b9-e0ae-acf2-b6d4e3995147",

And here were the results from a non-working host:

~ # vsish -e cat /hardware/bios/dmiInfo | head -5
System Information (type1) {
Product Name:
Vendor Name:
Serial Number:
UUID:[0]: 0x00

and the vim-cmd results:

~ # vim-cmd hostsvc/hosthardware | grep uuid -B 6
(vim.host.HardwareInfo) {
dynamicType = ,
systemInfo = (vim.host.SystemInfo) {
dynamicType = ,
vendor = "",
model = "",
uuid = "00000000-0000-0000-0000-000000000000",

So the BIOS of the Cisco Servers were not returning the smbios information. We rebooted the host and the issue persisted. We then powered off the host and unplugged the power cables for 5 minutes and then powered it back on and the values showed up without issues. When the host came back up, the ‘show mod’ had the new modules connected but it also had the old 0’ed modules as well. It looks like this:

switch# show mod | no-more
...
...
Mod Server-IP Server-UUID Server-Name
--- --------------- ------------------------------------ --------------------
1 192.168.1.139 NA NA
3 192.168.1.134 00000000-0000-0000-0000-000000000000 localhost1.
4 192.168.1.136 00000000-0000-0000-0000-000000000000 localhost2.
5 192.168.1.137 423416ec-385c-3be9-c26c-2f01b6b48ca7 localhost3.
6 192.168.1.134 42343a8f-65b9-e0ae-acf2-b6d4e3995147 192.168.1.134

We tried to remove the VEM module manually:

switch# conf t
Enter configuration commands, one per line. End with CNTL/Z.
switch(config)# no vem 3
ERROR: module 3 is inserted, cannot remove

But it failed. So we ran the following:

switch# system switchover

That failed over to the other HA standby VSM (if you have it setup) and then the stale module was gone. We did the same thing for the other host that had all zeros for it’s UUID and it worked just fine.

One last note, don’t confuse this UUID for the “System UUID”, they are two completely different UUIDs. To find out the “System UUID” you can do the following:

~ # grep uuid /etc/vmware/esx.conf
/system/uuid = "4ff35a91-ab62-fc60-8199-0050561721df"
~ # esxcfg-info -y | grep "System UUID"
|----System UUID.................................................4ff35a91-ab62-fc60-8199-0050561721df

VMware KB 1024791 talk about it’s uses. Here are a couple:

  1. For locking files
  2. Generating Mac Addresses for management interfaces

And I am sure there are lot of other VMware functions that rely on that value, but again it’s different from the “BIOS UUID”, which the Cisco VEM depends on. Here are both values seen from the same host:

~ # esxcfg-info -a | grep -E 'BIOS UUID|System UUID'
|----BIOS UUID................................................0x42 0x34 0x3a 0x8f 0x65 0xb9 0xe0 0xae 0xac 0xf2 0xb6 0xd4 0xe3 0x99 0x51 0x47
|----System UUID..............................................4ff35a91-ab62-fc60-8199-0050561721df

Published by Karim Elatov

14 January 2013

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