Cat 9500 and 9300 MTU conflicts

[kalen4101]

 Hello all,

  So I know with the Cat 9500 and 9300 it's a global config "system MTU xxxx" and this sets all interfaces to the new MTU. We are having issues of slowness to the VMware servers and in between servers. They are connected via 10G ports, ping is 1ms or less. So I was going to go into Vsphere and set the MTU to 9000 (max) on all switches and then set the  Cat 9500 to MTU 9000. Then also got to the 9300 which is also a 10G connection and increase it's MTU.

 Question is on all the other devices, for instance a ASA 55xx, or PC's plus  controllers for EMC and such? Are they going to have issues with the MTU mismatch?

 Should I go into the 9300 and set all 48 1 gig ports to "IP MTU 1500"? Then 9500 ports that are going to MTU 1500 devices?

[Reza Sharifi]

Hi,

The higher MTU is usually required for VMs and storage and not so much for users facing ports. So, if the 9500 is is device that provide connectivity between VMs, servers and storage than you need it on 9500, storage controllers and the VMs.

HTH

[kalen4101]

 Thanks for the response.

 So the 9300's I shouldn't bother with as they have only users and such, even though there is a 10G connect between them and the 9500?

[Reza Sharifi]

Correct. You don't need it on the user facing switches, as by default laptop/Desktop, printers, etc.. are not doing jumbo frames.

HTH

[Joseph W. Doherty]

"Question is on all the other devices, for instance a ASA 55xx, or PC's plus controllers for EMC and such? Are they going to have issues with the MTU mismatch?"

Depends on the host. In theory, any NIC receiving an oversized frame should consider it an error, but some NICs (like on many Cisco switches capable of jumbo Ethernet) will accept the frame. However, I understand, generally, such switches will not transmit a jumbo frame unless the port (perhaps via global setting) is configured for jumbo Ethernet.

One possible downsize of setting a Cisco device to a allow jumbo Ethernet, if not being used, the device might buffer fewer packets and/or frames since each can be potentially larger.