问题
Every host in an IPv4 network has a 1-second resolution real-time clock with battery backup. Each host needs to generate up to 1000 unique identifiers per second. Assume that each host has a globally unique IPv4 address. Design a 50-bit globally unique ID for this purpose. After what period (in seconds) will the identifiers generated by a host wrap around?
回答1:
There is a system which generates 1000 IDs per second.
You need to design a 50bit globally unique ID.
Now the IPv4 address of each host is already given to be unique. So using the IP within this ID would ensure that IDs generated on one host can't conflict on another (thus ensuring global uniqueness).
This leaves only a part of the full 50bit space available for the "unique" part of each generated ID; random or sequential doesn't matter.
The question can be reworded as follows:
How many bits are left for the "unique" part? And assuming that each hosts generates 1000 IDs per second, how many seconds do you need before you wrap around the available bit space?
来源：https://stackoverflow.com/questions/25201274/in-ipv4-network-finding-the-period-of-identifiers-generated-by-a-host-wrap-aroun