CompTIA Network+ (N10-009)Network OperationsHard
A DHCP server issues a lease with a total lease time of 8 hours. According to standard DHCP renewal timer behavior, at approximately what point into the lease will the client first attempt to renew its lease directly with the original DHCP server (T1 timer)?
- A4 hours (50%)
- B7 hours (87.5%)
- C1 hour (12.5%)
- D6 hours (75%)
Show answer & explanationAnswer & explanation
Correct answer: A. 4 hours (50%)
By default, the T1 renewal timer fires at 50% of the lease duration, so with an 8-hour lease the client attempts unicast renewal with the original server at the 4-hour mark (8 x 0.5 = 4 hours). If that fails, the T2 rebinding timer fires at 87.5% of the lease (7 hours), where the client broadcasts to any DHCP server.
Why the other options are wrong
- B. 87.5% corresponds to the T2 rebinding timer (7 hours), not the initial T1 renewal attempt.
- C. 12.5% is not a standard DHCP timer threshold used for T1 or T2.
- D. 75% is not the standard T1 or T2 default threshold.
DHCP T1/T2 Timers
T1 is the renewal timer that defaults to 50% of the lease duration, when the client unicasts a renewal request to the original server; T2 is the rebinding timer at 87.5% of the lease, when the client broadcasts to any DHCP server.
- T1 default = 50% of lease time (unicast renew)
- T2 default = 87.5% of lease time (broadcast rebind)
- If lease expires with no renewal, client must restart DORA process
Memory trick: Half the lease, try to renew; seven-eighths in, broadcast and plead.