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.
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
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,
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.
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