Connected: An Internet Encyclopedia
Restriction: Subnets within networks
Up: Connected: An Internet Encyclopedia
Up: Programmed Instruction Course
Up: Subnetting and CIDR
Prev: Routing Protocols Evolved
Next: Restriction: Fixed-length subnet masks

Restriction: Subnets within networks Subnets can't span across classful network boundaries. Each subnet must be fully contained with a single classful network. For example, 210.22.74/23 is not a valid subnet, because it spans two class C networks: 210.22.74.0 and 210.22.75.0. On the other hand, 150.22.74/23 is a valid subnet, because it is fully contained within the class B network 150.22.0.0.

Even if your routing protocols fully support CIDR, many operating systems disallow the use of subnets that would span classful networks. For this reason, it's usually a good idea to obey this restriction, even in full CIDR environments. You may get away with assigning 210.22.74/23 today, but later on try to attach a host to that Ethernet that refuses to recognize the 23-bit subnet mask.

Next: Restriction: Fixed-length subnet masks
Connected: An Internet Encyclopedia
Restriction: Subnets within networks

 

Dies ist ein Mirror von Connected: An Internet Encyclopedia von Brent Baccala. Die offizielle Projekt-Homepage findet sich im Web unter www.freesoft.org/CIE. Dieser Mirror wurde zuletzt aktualisiert am Samstag, 28 Januar 2006 18:17 +0100.