We are currently seeing a serious issue on NetScaler SDX 15000-50G appliances after upgrading to software release 14.1-66.55.
On affected systems, the 50G network interfaces that use Mellanox NICs do not come up after the upgrade. The underlying XenServer still detects the Mellanox 50G ports, but their link state remains “not connected”, so they cannot be used for network traffic. The 10G interfaces are not affected and continue to work as expected.
We also have SDX 15000-50G devices equipped with Fortville interfaces, which so far do not show this behavior. This suggests that the problem is limited to the 50G Mellanox-based ports on this platform.
A Priority 1 support case is open with Citrix, and we are already in contact with Product Management to analyze the root cause and identify a fix. Until there is an official statement or patch from Citrix, we strongly recommend postponing upgrades of NetScaler SDX 15000-50G systems to 14.1-66.55, especially where 50G Mellanox interfaces are in use.