Address reserved for standby server question

Question

_{Wednesday, November 6, 2019 2:13 AM}

Hi,

In hotstandby mode does the field "Address reserved for standby server" mean that only a certain percentage is leased out by the primary server? Say for the standby server the address reserved is 40% does that mean only 40% is leased out by the primary?

Thanks,

Janus

All replies (6)

_{Wednesday, November 6, 2019 7:19 AM ✅Answered}

Hi ,

>>So in this scenario if address reserved for standby server is set to 30% and primary is leasing already 90% of the ip addresses and it goes down, only 10% free will be taken over by the standby?

No, the primary will not lease the IP address more than 70%. 30% of the IP address will be reserved and not be leased by primary server.  

>>What if only 50% is leased out by the primary and it goes down, would the standby server just take 30% free or will it take the 50% free?

If address reserved for standby server is set to 30%, the standby server will just take 30% free.

Best Regards,

Candy

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_{Wednesday, November 6, 2019 5:32 AM}

Hi ,

"In a hot standby failover mode, free IP address pool is owned by the Active server entirely as it is serving all the client requests. In the event of an outage of the active server, the standby server needs to be able to renew existing IP address leases as well as give out new IP address leases to clients who request a new lease. For the later scenario – leasing new IP addresses to clients, the standby server needs a free IP address pool available to it from which it can give out new leases.

The standby server will take over the free IP address pool of the active server only after it transitions into Partner Down state from Communicated Interrupted state and a time period of MCLT (Maximum Client Lead Time) has expired.

To enable the standby server to serve new IP address leases to clients during this interim period - i.e. till it transitions to Partner Down and takes over the entire free IP address pool of a scope – a percentage of free IP address pool needs to be available to standby server. "

This is the function of reserve address percentage. In addition, since the reserve address percentage is used in an interim period as discussed above, the value chosen for it can typically be small (5-10%).

For more details about it , please refer to the following article:

DHCP Failover Hot-Standby Mode

If you have anything unclear , please free feel to let me know.

Best Regards,

Candy

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_{Wednesday, November 6, 2019 7:01 AM}

So in this scenario if address reserved for standby server is set to 30% and primary is leasing already 90% of the ip addresses and it goes down, only 10% free will be taken over by the standby?

What if only 50% is leased out by the primary and it goes down, would the standby server just take 30% free or will it take the 50% free?

_{Thursday, November 7, 2019 1:39 AM}

Hi ,

Just checking in to see if the information provided was helpful.

Please let us know if you would like further assistance.

Best Regards,

Candy

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_{Thursday, November 7, 2019 1:53 AM}

Thank you so much Candy Luo! You have been very helpful!

_{Thursday, November 7, 2019 1:57 AM}

Hi ,

I am pleased to know that the information is helpful to you!

Have a nice day!

Best Regards,

Candy

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