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May222012

Configuring Jumbo Frames on Cisco Data Center Switches

Ethernet jumbo frames are a common requirement in data center networks, especially ones that rely on Ethernet based storage protocols such as NFS and iSCSI. Jumbo frames are not enabled on Cisco switches by default - here are the commands to configure the larger MTUs on the most common switches seen within the data center.

Nexus 5000s and 5500s

Enabling jumbo frames on the Nexus 5000/5500 platform is done via a policy-map. When applied using class-default, jumbo frames are enabled across the whole switch.

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

Note: The MTU parameter in “show interface” will continute to show a value of 1500. The best way to verify that jumbo frames is enabled is to setup a ping across the switch to endpoints that are also configured with jumbo frames using a packet size of 9216 and the “do not fragment” bit set (e.g. another switch, a server, NAS controller, etc…).

ping 10.10.10.10 packet-size 9216 df-bit count 10

Nexus 7000

Jumbo frame configuration on the Nexus 7000 is much simpler. Simply set the system jumbo MTU in global config mode:

switch-n7k(config)#system jumbomtu 9216

Then specify the MTU for specific interfaces

switch-n7k(config)#interface ethernet x/x
switch-n7k(config-if)#mtu 9216

MTU settings on individual interfaces can be verified via the “show interface” command:

 switch#sh interface vlan10
 Vlan100 is up, line protocol is up
  Hardware is EtherSVI, address is  4055.3927.2cc1
  Description: Sample
  Internet Address is 10.10.10.1/24
  MTU 9216 bytes, BW 1000000 Kbit, DLY 10 usec,

Catalyst 6500 (IOS Native Mode)

Configuring jumbo frames on a 6500 also requires simply setting the MTU on the individual interfaces:

switch-6500(config)#int GigabitEthernet1/1
switch-6500(config-if)#mtu 9216

Verify using the “show interface” command.

Reference

Cisco.com Configuration of Jumbo MTU on Nexus 5000 and 7000 Series

Cisco.com Jumbo/Giant Frame Support on Catalyst Switches Configuration Example

JasonNash.com Enabling Jumbo Frames on the Cisco Nexus 1000v

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