[c-nsp] Nex3K and MTU

CiscoNSP List CiscoNSP_list at hotmail.com
Thu Mar 3 17:30:37 EST 2016

Thanks very much Christophe - why does "sh int port-chan 10" show mtu of 9216?  Shouldnt it show 1500bytes?

# 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

And Id love to know the logic behind the decision to use qos to "change" mtu, on this platform....seems the larger Nexus's you can change it on a per Int basis?  lol....Or is logic a paradox when it comes to the differences between Cisco platforms/OS's/Feature disparities...

From: Christophe Fillot <cf at utc.fr>
Sent: Thursday, 3 March 2016 7:34 PM
To: CiscoNSP List; cisco-nsp at puck.nether.net
Subject: Re: [c-nsp] Nex3K and MTU

On 03/03/2016 02:10 AM, CiscoNSP List wrote:

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

To see the real MTU you have to use "show queuing interface <phys_int>".
For example:

# sh int e1/45
Ethernet1/45 is up
 Dedicated Interface

  Hardware: 1000/10000 Ethernet, address: 8c60.4f96.2cf4 (bia 8c60.4f96.2cf4)
  Description: storage2-01
  MTU 1500 bytes,  BW 10000000 Kbit,, BW 10000000 Kbit, DLY 10 usec

# sh queuing int e1/45
n5k-pg2-a# sh queuing int e1/45
Ethernet1/45 queuing information:
  TX Queuing
    qos-group  sched-type  oper-bandwidth
        0       WRR            100

  RX Queuing
    qos-group 0
    q-size: 100160, q-size-40g: 100160, HW MTU: 9216 (9216 configured)
    drop-type: drop, xon: 0, xoff: 0

Hope this helps


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