Enabling Jumbo Frames on N7K VPC Peer Link

[Saroj Pariyar]

I have a 2 Nexus 5k's in a VPC environment. These 2 N5K's connect to the 2 upstream Catalyst 6500. Right now the the port-channels connecting from Nexus 5K's to Catalyst 6500 are enabled with jumbo frames(mtu 9216). As a part of migration work, i am migrating the uplinks from  Catalyst 6500 to Nexus 7000.So my new uplinks from Nexus 5000 will be connecting to Nexus 7000.When i migrate the uplinks to Nexus 7000, i will enable the jumbo frames on the VPC port-channel between Nexus 5000 to Nexus 7000. But my question here is: do i need to enable the jumbo frames(mtu 9216) on the peer link between Nexus 7k also. Please let me know if anyone has gone thruough this issue.

I have attached the diagram of my topology after i migrate to Nexus 7k.

[glen.grant]

   If you are going support jumbo frames throughout your N7k's then yes I would enable it on the peer links.

[Vasilii Mikhailovskii]

Hello.

Per my understanding, jumbo frames are enabled on peer-link by default.

[Saroj Pariyar]

But when i do.... "sh run int po1 all"  i don't see mtu 9216 config over there. In my case, Port-channel 1 is a peer links between Nexus 7K. Could you please let me know how can i verify jumbo frames has been enabled on the peer link.

[Marc Espina]

Saroj,

I believe that mtu 9216 is on the VPC peer-link by default. I attempted to configure it in our lab and received an error when trying to apply it to the port-channel. I then did a show interface and noticed that the MTU was already at 9216.

interface port-channel10
  switchport mode trunk
  switchport trunk allowed vlan 1,810-813,820-823,900
  spanning-tree port type network
  vpc peer-link

N9k-1(config-if)# int p10
N9k-1(config-if)# mtu ?
  <1500-9216>  Enter MTU
N9k-1(config-if)# mtu 9216
ERROR: port-channel10: Cannot configure port MTU on Peer-Link.

N9k-1(config-if)# sho int p10
port-channel10 is up
admin state is up,
  Hardware: Port-Channel, address: f4cf.e237.a524 (bia f4cf.e237.a524)
  MTU 9216 bytes, BW 80000000 Kbit, DLY 10 usec
  reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation ARPA, medium is broadcast

[Kevin Dorrell]

It is a relief to read that!  I thought I was going to have to configure the peer-link MTU on-the-fly, with all the potential production impact that might have!  So thank you.

Kevin

[gijohngeorge]

The interface port-channel command shows MTU as 9216 bytes - refer below.

port-channel1 is up
admin state is up
Hardware: Port-Channel, address:
Description: *** VPC PEER LINK ***
MTU 9216 bytes, BW 40000000 Kbit, DLY 10 usec
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, medium is p2p
Port mode is trunk
full-duplex, 10 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: Eth3/1, Eth3/2, Eth3/3, Eth3/4
Last clearing of "show interface" counters never
1 interface resets
Load-Interval #1: 30 seconds
30 seconds input rate 2598456 bits/sec, 1645 packets/sec
30 seconds output rate 4990280 bits/sec, 1959 packets/sec
input rate 2.60 Mbps, 1.64 Kpps; output rate 4.99 Mbps, 1.96 Kpps
Load-Interval #2: 5 minute (300 seconds)
300 seconds input rate 2601888 bits/sec, 1628 packets/sec
300 seconds output rate 3602864 bits/sec, 1694 packets/sec
input rate 2.60 Mbps, 1.63 Kpps; output rate 3.60 Mbps, 1.69 Kpps
RX
166999124 unicast packets 148259719013 multicast packets 982582596 broadcast packets
149409300727 input packets 30167886083411 bytes
6 jumbo packets 0 storm suppression packets
0 runts 0 giants 0 CRC/FCS 0 no buffer
0 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
5872330332 unicast packets 151062855918 multicast packets 708037234 broadcast packets
157643223427 output packets 34790642329431 bytes
3 jumbo packets
0 output error 0 collision 0 deferred 0 late collision
0 lost carrier 0 no carrier 0 babble 0 output discard
0 Tx pause

But when running the following command, MTU is shown as 1500 bytes:

# show system internal ethpm info interface port-channel 1 | egrep -i mtu
medium(p2p), snmp trap(on), MTU(1500),

Any reason why there is a discrepancy?