[c-nsp] Nex3K and MTU

[CiscoNSP List]

Ok - Well another "surprise" for me on these boxes, you cant set MTU the "normal" way (Well normal for me, coming from Cat/routers)...i.e. you cant set it globally (system mtu), nor per Int...you have to do it via QOS(Interesting decision by NXOS developers lol)


Anyway - What Im a little confused about is this....the 3Ks automatically place a rather extensive "default" QOS policy (Copp/control plane), which doesnt have any reference to an MTU of 9216.


QOS to "add" MTU of 9216 is this (From what Ive researched):

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


Without this added though, VPC link (20Gb portchan), it is stating MTU of 9216:

# sh int port-channel 10
port-channel10 is up
  Hardware: Port-Channel, address: 30f7.0da0.7378 (bia 30f7.0da0.7378)
  Description: 20Gb_VPC_PEER_LINK_TO_TORSW02-EQ-SY3-1806B
  MTU 9216 bytes, BW 20000000 Kbit, DLY 10 usec
  reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation ARPA
  Port mode is trunk



Yet "other" ports show 1500bytes:

# sh int eth 1/1
Ethernet1/1 is down (Link not connected)
Dedicated Interface
  Hardware: 10/100/1000 Ethernet, address: 547f.ee7b.ff28 (bia 547f.ee7b.ff28)
  MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec
  reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation ARPA
  Port mode is access


Where is the switch getting this 9216mtu for the VPC/Portchan link from?  (It def. isnt set on the member Ints(You are unable to set MTU on Ints on these boxes), and you cant set it globally)?


Cheers