NX7000 - MTU Size

[sadik.bash]

Hello,

I configured 4 port channels with mtu size 9000. The VM engineers requested me to configre the same mtu size on the vlans assiged to those 4 port channels. I wasn't sure if I needed to configure the MTUs on the VLANs since I already configured them on the port channels.

My question is, do I need to set the MTU size per VLAN if I already set it up on the port-channel?

Thanks in advance, ~sK

Example of the port channel and vlan config:

interface Vlan101

  ip address 172.22.101.253/24

  ip router eigrp 10

  hsrp version 2

  hsrp 101

    preempt

    priority 90

    timers  2  6

    ip 172.22.101.254

  ip dhcp relay address x.x.x.x

  ip dhcp relay address x.x.x.x

  no shutdown

  delay 2000

interface Ethernet6/1

  description ESX-BC-11(#1)

  switchport

  switchport mode trunk

  switchport trunk allowed vlan 68,71,100,108-113,119,136,152,175

  switchport trunk allowed vlan add 202,214,221,223,231-232,241,243

  switchport trunk allowed vlan add 300,800,1200,1300-1302,1321,1400

  switchport trunk allowed vlan add 1600,1800,3712

  spanning-tree bpduguard enable

  mtu 9000

  channel-group 11

  no shutdown

[Steve Fuller · Accepted solution]

Hi,

The ESX host will be able to communicate with other systems in the same VLAN with 9000-byte jumbo frames, but if the traffic from the ESX host will be routed via the SVI i.e., interface vlan 101, then you will need to change the MTU on the SVI with the mtu interface sub-command, where is the maximum frame size you want to allow.

If you don't set this, when the ESX host tries to route any jumbo frames, the router will respond with an ICMP Type 3 Code 4 message (Fragmentation Needed and Don't Fragment was Set) causing the host to reduce the maximum packet size it sends.

Regards