Enabling Jumbo Frame to lmprove Network Performance

 

 


 

Jumbo Frames: is a frame with a payload greater than the standard maximum transmission unit (MTU) of 1,500 bytes. Jumbo frames can carry up to 9000 bytes of payload. Enabling jumbo frames can improve network performance by making data transmissions more efficient, and with less protocol overhead.

But before enabling Jumbo frame, you need to consider the network must support Jumbo frames end-to-end and configure the entire network path, including:

    • VMkernel adaptor
    • Virtual switches
    • Hosts NICs
    • Physical switches
    • Routers
    • Storage devices

You don’t have to use jumbo frames everywhere, and in many cases, they are not needed; With the granularity vSphere networking offers, it is possible to have different MTU settings in your environment. For example, you may want to configure the storage connectivity to use jumbo frames while the virtual machines use the standard 1500 MTU.

The most common application of jumbo frames is on IP storage networks such as iSCSI, NFS, and vMotion networks. These networks are generally closed, and device configuration can be governed. Enabling jumbo frame support on a virtual machine requires a VMXNET3 adapter, and inside the guest operating system, configure the network adapter to allow jumbo frames.

 

For routers and switches must have ports set to an MTU that is greater than 9000 (packet header + packet data). Check the manufacturer’s recommendation when changing these settings, but on a router or switch 9216 is a common MTU size that accommodates an Ethernet packet with a 9000-byte payload. 

Remember: changing one point without changing all related VMkernels or targets. This can cause issues such as vMotion failing, vSAN hosts becoming isolated, or external storage losing connectivity. Mismatched MTU settings cause dropped packets isolating or degrading hosts’ or target’s connectivity. Missing any device or misconfiguring devices for jumbo frames will cause intermittent issues.

 

That being said, you need to check whether the hardware in your environment supports a jumbo frame or not? Then you will begin by changing the MTU for the vMotion only, and its recommended start for one cluster to ensure there is no issue; then you will move to another cluster. Also, When changing the MTU size on a vDS, the attached physical NICs are brought down and up again instantly. This causes a very brief network outage on the vDS.

 

After enabling jumbo frames, it’s important to test connectivity between all devices, by using the Ping command that includes specific parameters to have a packet size larger than 1500, and without fragmenting the packets:

For VMWare: vmkping -I vmk3 -s 9000 -d [Destination_IP]
-I vmk3 tells vmkping to use the interface vmk3 as the source of the packets.

-s 8000 tells vmkping to send an 8000-byte payload.

-d tells vmkping to set the don’t fragment bit (DF). 

For Windows: ping [Destination_IP] -l 9000 -f 

For Linux: ping -s 9000 -M do [Destination_IP] 

 

Making sure that pings are going out the correct interface during the test. Virtual machine hosts, switches, and routers all have multiple ports, networks, and VLANs configured. Then you need to observe the environment for a couple of days.

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