How do I enable jumbo frames on externally managed switches?

Infrastructure & Networking Switches and Gateways
1

I purchased a Mellanox MSB-7890 36-port 4x EDR IB externally managed switch a while ago and my question is how do I enable jumbo frames (i.e. MTU=9216) on it?

Your help is greatly appreciated.

Thank you.

2

Hello Ewen,

Many thanks for posting your question on the Mellanox Community.

Based on your question, we want to clarify the MTU on an InfiniBand network. By default the MTU on an InfiniBand network is set to 4K. You cannot change this InfiniBand MTU size.

However, when you run IPoIB, you can change the IPoIB MTU size, based on the mode, connected or datagram, to respectively 2K, 4K for datagram mode or 65K for connected_mode.

For more information on IPoIB MTU, we recommend to review the following links:

https://docs.mellanox.com/pages/viewpage.action?pageId=12013510

https://www.rdmamojo.com/2015/04/21/working-with-ipoib/

Many thanks,

~Mellanox Technical Support

3

I’ve also tried this as well.

But whenever I try to change the MTU on the adapter, it even in connected mode, it says that it’s an invalid configuration because according to ibv_devinfo, the max MTU that it can have is 4kiB.

So, it will only take 4092 as the maximum MTU that I can set in /etc/sysconfig/network-scripts/ifcfg-ib0.

Again, I am using CentOS 7.6.1810.

Thanks.