MTU and jumbo frame on nexus 9k

[jimirobinson]

I'm seeing jumbo frame incrementing RX and TX however show interface shows MTU set at 1500.

port-channel51 is up
admin state is up,
vPC Status: Up, vPC number: 51
Hardware: Port-Channel, address: 00b7.712e.4580 (bia 00b7.712e.4580)
Description: bondup
MTU 1500 bytes, BW 160000000 Kbit, DLY 10 usec
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, medium is broadcast
Port mode is trunk
full-duplex, 40 Gb/s
Input flow-control is off, output flow-control is off
Auto-mdix is turned off
Switchport monitor is off
EtherType is 0x8100
Members in this channel: Eth1/51, Eth1/52, Eth1/53, Eth1/54
Last clearing of "show interface" counters 18:33:21
0 interface resets
30 seconds input rate 6279336 bits/sec, 1294 packets/sec
30 seconds output rate 4351224 bits/sec, 898 packets/sec
Load-Interval #2: 5 minute (300 seconds)
input rate 21.68 Mbps, 2.41 Kpps; output rate 7.79 Mbps, 1.09 Kpps

RX
342713802 unicast packets 10582812 multicast packets 8336704 broadcast packets
361653357 input packets 434870808283 bytes
262958908 jumbo packets 0 storm suppression bytes
0 runts 20039 giants 0 CRC 0 no buffer
20039 input error 0 short frame 0 overrun 0 underrun 0 ignored
0 watchdog 0 bad etype drop 0 bad proto drop 0 if down drop
0 input with dribble 0 input discard
0 Rx pause
TX
164370593 unicast packets 2305329 multicast packets 79862 broadcast packet
s
167274585 output packets 155818320925 bytes
83969134 jumbo packets
518801 output error 0 collision 0 deferred 0 late collision
0 lost carrier 0 no carrier 0 babble 0 output discard
0 Tx pause

[Mark Malone]

Hi
is it set somewhere globally ? with this system jumbomtu 9216 or something similar
that would override the interface settings

[jimirobinson]

it's not set globally but I've just read this :

In the case of 40-G interfaces, since the MTU limit check is disabled, it ignores the packet size and traffic flows irrespective of its MTU.

[Mark Malone]

hmm wasnt aware of that , it states just 9372s in the community post i seen of it , im checking 9k docs to see if i can find it too , if theres any more on it

[Reza Sharifi]

In the case of 40-G interfaces, since the MTU limit check is disabled, it ignores the packet size and traffic flows irrespective of its MTU.

Eth1/51, Eth1/52, Eth1/53, Eth1/54

So, this is not a 40G interface natively.  These are 4 10Gigs.

HTH

[Joseph W. Doherty]

I recall a Cisco SE telling me that many Cisco switches, that are jumbo capable, will accept jumbo frames even if not configured for them. However, they won't forward/transmit a jumbo frame unless configured to do so.