CIDR

EdTheLad

Whats the difference between, CIDR and network summarization?
For me they are the same thing why are there different names for the same thing?

darkuser

cidr is classless interdomain routing.

I'ts a way to carve up networks to you're liking. (make smaller)
summarization is used to advertise a "summary route" of larger address space for downstream networks.
(make bigger for purpose)

make sense ?
hth

tunerX

The Classless in CIDR means that you do not have to obey the class A,B and C requirements of back in the day. Before CIDR if you had a Class C address 192-223 then then you could only get 8 bits of addressing. An example with CIDR is that you can run 192 with a 16 bit mask and get 16 bits of addressing. A system that does not support CIDR will only let you enter Class based addresses and masks. I don't think there are too many TCP stacks that do not support CIDR.

Route summarization is a broad concept. It can include the use of both CIDR and VLSM.

You can subnet a class C with 2 bits and get 4 networks. If all of those subnets are reachable through a single system or set of systems then you can then summarize your advertisement so only the actual class C network and mask are advertised or used for routing decisions. You used summarization and VLSM but did not use CIDR since you never broke the class based boundary.

You can have 4 class C networks all reachable through a single system or set of systems and use CIDR to "break" the original class C boundary by using left most bits as the mask. You can call this summarization but it is usuall referred to as aggregation.

192.168.0.0 255.255.255.192
gives networks
192.168.0.0
192.168.0.64
192.168.0.128
192.168.0.192

summarized as 192.168.0.0 255.255.255.0 but is still an original class C address and network by definition.

With CIDR you can have the following 4 networks.

192.168.0.0 255.255.255.0
192.168.1.0 255.255.255.0
192.168.2.0 255.255.255.0
192.168.3.0 255.255.255.0

You can aggregate the routes by using CIDR

192.168.0.0 255.255.252.0

This resembles a subnetted class B but the address space was originally defined as that of a class C. So summarization allows you to aggregate to the original network boundary CIDR allows you to aggregate past the network boundary.

EdTheLad

Great explanation turnerX,i wish the books could put it so clearly!
Thank you kindly.

dissolved

tunerx is definitely the man

AceAll

That was pretty good explanation turnerX