Solved: Multi-site / Multi-Pod MTU Jumbo Frames

Fernando Hernández · ‎07-14-2020

Hey Hello guys.

I would like to know if its necessary to use a 9216 MTU for Multi-site and Multi-Pod on the ISN/IPN or if I can use a 9000 MTU size.

I have on the network jumbo frames enabled with an mtu size of 9000 on the Cisco devices, but I would like to know if needed to be changed to 9216 for Multi-site or Multi-Pod. (Some of these devices will be used for the ISN/IPN).

Francesco Molino · ‎07-14-2020

Hi

It will depend on your endpoints configuration.
If your endpoints send a frame of 1500, 9000 is well enough because vxlan add a 50 bytes overhead (or 54 bytes if 802.1q is preserved).
However, if your endpoints are sending the maximum mtu frame 9000, then you'll need to increase it to avoid fragmentation for vxlan.

Thanks
Francesco
PS: Please don't forget to rate and select as validated answer if this answered your question

View solution in original post

Francesco Molino · ‎07-14-2020

Hi

It will depend on your endpoints configuration.
If your endpoints send a frame of 1500, 9000 is well enough because vxlan add a 50 bytes overhead (or 54 bytes if 802.1q is preserved).
However, if your endpoints are sending the maximum mtu frame 9000, then you'll need to increase it to avoid fragmentation for vxlan.

Thanks
Francesco
PS: Please don't forget to rate and select as validated answer if this answered your question

Fernando Hernández · ‎12-10-2020

I have read on documentation that they use 9150 for IPN/ISN. But Could I use the maximum 9216?

Robert Burns · ‎12-10-2020

@Francesco Molino Yes of course. Packet sizes are set by the source device. Any device in the path only needs to support that minimum value. Anything larger is fine and wont hurt anything. With ACI, but default the control plane MTU is 9000B. Add another 50 bytes for VXLAN and you're still under 9100. Anything larger is fine.

Robert