Issues have been reported when upgrading from NetScaler 11.1 Build 56.19 to 11.1 Build 57.11. The secondary NetScaler crashes continuously when syncing the DHT sessions from primary NetScaler.

1. Customer is using HA and upgrading from 11.1.x to  11.1.57.11.
2. During upgrade at one point of time one NetScaler will be at 11.1.57.11 and other NetScaler will be at lower version.
3. At that point of time there will be crash if DHT namespace sync happens between primary and secondary. Typically DHT  sync happens to sync the active traffic sessions between primary and secondary. So if any traffic is running on the box there is highly likelihood of DHT sync resulting in crash

If you want to upgrade from NetScaler 11.1-56.x or older 11.1 builds to the latest 11.1 build, then the recommended builds are 11.1-57.13 or 11.1-58.x build, once it becomes available.

If customer has already downloaded and upgraded to 11.1.57.11, then customer need not do anything .The issue is seen only during upgrade when primary and secondary are of different NetScaler versions. So if the upgrade is successful then there is no action required.

Problem Cause

This is due to the change in the order of the DHT namespace between 11.1 Build 56.19 and 11.1 Build 57.11. So the issue will be seen if customer upgrades from 11.1.x to 11.1.57.11. But the issue will not be seen when customer upgrades from 11.0 or below build and the reason being NetScaler during upgrades between major version the DHT namespace is expected to be different and NetScaler handles the difference gracefully.