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  • HAN WANG thinks this is interesting:

CIDR masks are not limited to a site but are instead visible to the global routing system. Thus, the core Internet routers must be able to interpret and process masks in addition to network numbers.

From

Cover of TCP/IP Illustrated, Volume 1: The Protocols

Note

The difference between VLSM and CIDR is that CIDR masks are not limited to a site bu are instead visible to the golbal routing system. In other words, VLSM only works on a local site.