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Jumbo frames Nexus 3k along with other traffic


Hi Guys

Probably a bit noobish question - how do we enable jumbo frames on Nexus 3k device. We have server VLAN and all my Windows server traffic such as DNS, DHCP SMB etc is going through there along with iSCSI traffic. 

We also have separated VLAN for clients and another VLAN for VOIP.

From what i'm reading seems like jumbo frames on Nexus 3k are enabled on the whole device which means that will effect all VLANs... what would be the impact on VOIP and regular clients traffic? 

Any feedback is greatly appreciated!




2 Replies 2

Reza Sharifi
Hall of Fame Expert Hall of Fame Expert
Hall of Fame Expert

Hi Chris,

That is correct.  You enable it for the whole device.  Enabling it this way does not have any impact on other vlans and/or client traffic.  Here is a sample config

policy-map type network-qos jumbo
class type network-qos class-default
mtu 9216
system qos
service-policy type network-qos jumbo


Joseph W. Doherty
Hall of Fame Master Hall of Fame Master
Hall of Fame Master
". . . what would be the impact on VOIP and regular clients traffic? "

Usually not, but there a couple of potential conflicts.

First, one possible area of impact, again unlikely, would be using jumbo frames might use up buffer RAM sooner than standard size Ethernet frames, which might impact even non-jumbo sized frames. (Not too likely on a Nexus, more of a concern on low end edge switches.)

Second, again unlikely, assuming your edge ports are high speed, a preceding jumbo frame (or frames) will delay a following VoIP frame longer (as jumbo size frames take longer to transmit). (For this issue, if you think QoS will mitigate, it will, but not totally. Again, though, for high speed [e.g. gig] ports the extra delay is generally not an issue for VoIP. If you're concerned about extremely low latency apps [i.e. the type where you need to use cut through switching], then it might become an issue.)
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