HCX PMTU mismatch alarm

Products

• VMware HCX

Issue/Introduction

In some situations where HCX uplink traffic might be double encapsulated, first from the HCX IPsec and second from an upstream IPsec encapsulation it might be necessary to lower the uplink MTU to give headroom for the headers. Due to this extra required header space, HCX can give an alarm since the maximum MTU value is not being used even though it does not affect the actual flow of traffic. 

Environment

VMWare HCX

Resolution

Since this is a function of the PMTU check working as expected, the alarm will need to be reset to green from the HCX or vCenter UI.