I still don't have an understanding of how exactly "Maximum Client Lead Time" works.
I have even done some testing by in my environment everything just works which is suspicious and I wan to have a better understanding before implement this on the production server.
The first question - am I right that "Maximum Client Lead Time" is completely irrelevant if the IP address is reserved for this particular mac address. So the client PC will get the same reserved IP address from either of the servers anyway? Even if one of them is down and "Maximum Client Lead Time" is expired?
To give my questions some context I will explain what my test environment is.
I have two servers in "load balance mode" let's say 50 - 50. (I suppose they divide the zone of authority like - 192.168.1.1 -> 192.168.1.128; 192.168.1.129 -> 192.168.1.256). let's name them server1 and server2 respectively.
Maximum Client Lead Time - 10 hours.
Auto State Switchover Interval - 1 hour.
The global maximum lease time is 8 days. (it is in the scope's options).
My client (PC1) gets an IP address from DHCP server1 - 192.168.1.44 (lease time is 8 days).
Just suddenly server1 goes down. What will happen then?
Am I right that if the PC1 stays online for 8 days straight, the IP address will stay the 192.168.1.44 for all this time? And after this, it will try to automatically renew the IP address from the server2. And it will get an address in the range that starts from 192.168.1.129.
What will happen if the PC1 is restarted just after the server1 has gone down? I suppose it will try to renew its address, in this case, it must try to reach server2. What address will it get? Will it continue to use 192.168.1.44 (that has been given by server1) for 10 hours (Maximum Client Lead Time). Or will it use it for 8 days? What will happen after "Auto State Switchover Interval" has expired - does it mean that the server2 will start to give out scope form 192.168.1.129 only for new clients or if the PC1 released the previous address?
What will change after "Maximum Client Lead Time" has been expired? Will it no longer try to prolong the IP address lease after 8 hours? Or will it try to prolong all addresses for 8 days?
The short explanation for MCLT is that having a too-small value will cause performance problems in normal operation (but will indeed buy you a quicker recovery if one of the pair fails).
Why is that? How is MCLT can cause performance problems? I thought (maybe wrongly) that "Auto State Switchover Interval" can cause performance problems because it will send a lot of messages to ask the second server about its status.
And how the low MCLT value could help to recover faster? Does it only apply to newly added devices? So if the client already was given an address before server1 had crashed, it really won't matter?
Is there a big difference in these options for “Hot Standby” and ”Load balance“ modes?
In the case of DHCP failover, the downtime is minimal and can basically be ignored.
From the perspective of the client, it is basically impossible to detect downtime.
>>In what circumstances will not Client1 be able to gen an IP address? (Considering that one of the two servers is working).
Generally, client 1 should be able to get an IP address when one DHCP is working. If it can't get IP address then we need to do further troubleshooting like analyzing network traffic.
Am I right that regardless of the "Maximum Client Lead Time" setting of 10 hours, one hour, or several days, the client will notice nothing in any case?