Now my questions are:
a) Do i always need to power off the module before the replace? What is the best practice in module replacement?
No, switching modules are hot-swappable. See below.
Hot Swapping Switching Modules
You can remove and replace switching modules without powering down the switch. This feature is known as hot swapping.
When you remove or insert a switching module while the switch is powered on and operating, the switch does the following:
1. Determines if there is sufficient power for the module.
2. Scans the backplane for configuration changes.
3. Initializes all newly inserted switching modules, notes any removed modules, and places them in the administratively shutdown state.
4. Places any previously configured interfaces on the switching module back to the state they were in when they were removed. Any newly inserted interfaces are put in the administratively shutdown state, as if they were present (but unconfigured) at boot time. If you insert a similar switching-module type into a slot, its ports are configured and brought online up to the port count of the original switching module.
The switch runs diagnostic tests on any new interfaces. If the test passes, the switch is operating normally. If the new switching module is faulty, the switch resumes normal operation but leaves the new interface disabled.
If the diagnostic test fails, the switch crashes, which usually indicates that the new switching module has a problem in the bus and should be removed.
b) What can be the creason of the OSPF flapping on other modules?
I thought you saw the following error on that module:
" %DIAG-SP-3-MAJOR: Module 1: Online Diagnostics detected a Major Error. "
The above could also mean the line card is not properly seated. Re-seat that line card and see if it fails the diagnostic again.
