Final answer:
The default NHRP cache timer is 2 hours, which is the duration an NHRP entry remains in the cache before it needs to be refreshed.
Step-by-step explanation:
The default NHRP (Next Hop Resolution Protocol) cache timer is 2 hours. This time value is the duration that an NHRP entry will remain in the cache before it is considered stale and therefore must be refreshed. NHRP is used in technologies such as DMVPN (Dynamic Multipoint Virtual Private Network) to dynamically discover the IP address of the next hop server or router.
In the context provided, with regards to the amount of time passed, such as 0 (before any time has passed), 1 hour (1 half-life), and 2 hours (2 half-lives), the default NHRP cache timer would correspond to the duration mentioned for 2 half-lives, which is 2 hours.
NHRP stands for Next Hop Resolution Protocol, which is a protocol used in computer networking to map virtual private network (VPN) end devices to their physical network addresses. The NHRP cache timer determines how long an entry will stay in the cache before being automatically removed if it is not refreshed. In the case of the default NHRP cache timer, entries will automatically be removed after 30 minutes if they are not refreshed.