Order and Impact of implementing Jumbo Frames UCS Environment

[CiscoMedMed]

I have Jumbo frames enabled at the upstream Nexus 9k switch and on one of the classes in QoS System Class in LAN/LAN Cloud. I'm wondering which operations in the enabling of jumbo frames could impact traffic flows.

1) Enabling 9000 frame size in remaining QoS System Class.  Impacting or not? (I think not.)

2) Applying a new vNIC template with MTU 9000 to a server . Impacting of not> (I think yes)

3) VMWare Distributed Switch MTU change to 9000.

https://www.cisco.com/c/en/us/support/docs/servers-unified-computing/ucs-b-series-blade-servers/117601-configure-UCS-00.html

[Sergiu.Daniluk · Accepted solution]

Hi @CiscoMedMed 

Adjusting/modifying the vNIC template requires a blade reboot (supposing you have an updating template). If you have the service profiles set to UserACK (in the maintenance policy) , then you can do the changes and perform the reload one server at a later time when you want. If not, then all affected blades (where the vNIC template is used) will reboot once you click OK.

All the other steps are not impacting.

Stay safe,

Sergiu

[Steven Tardy · Accepted solution]

#1 CAN cause a short pause/drop in network traffic when doing some changes QoS parameters. Enabling/disabling classes for sure will cause a <1second hiccup. Some changes on some platforms will even reboot the Fabric Interconnect[1]. Changing just Best Effort MTU should not impact, but don't know for sure.

99% of the time UCS QoS changes to unnoticed, but have seen a handful of instances where applications get grumpy when UCS QoS changes make the network "go away" for just a moment.

[1] https://www.cisco.com/c/en/us/td/docs/unified_computing/ucs/ucs-manager/GUI-User-Guides/Network-Mgmt/4-2/b_UCSM_Network_Mgmt_Guide_4_2/b_UCSM_Network_Mgmt_Guide_chapter_01000.html

#2 Like Sergiu said should prompt for server reboot.

#3 Haven't ever seen this cause an issue, but I'm not VMware TAC either to see the corner cases where it could.