VLSM

[krazychinaman]

So i was reviewing on vlsm....i was thinking why do we use vlsm...? i understand vlsm save alot of number of ip....but let say you are using all private ip address...cant you just use a classful address....? and isnt reallly the only time you really use vlsm is when isp give you like a block of ip address?

[warriorfan808]

Just keep in mind management. The smaller your network, the least important. The thing is, it's much easier to manage addresses when you advertise what you use, rather than the entire classful network. Also think of it in terms of security. You want to have complete domination of your entire network topology and the ability to define routes the way you choose. Also, VLSM comes into play when you're dealing with supernetting. One supernetted advertisement can ease route processing and have your network function a lot better.

For example, lets use some class C addresses:

192.168.5.0 /24
192.168.6.0/24
192.168.7.0/24

These three can be advertised as 192.168.4.0/22

Also keep in mind that in order to get the best functionality of your newer routing protocols, you're better off using VLSM.

[krazychinaman]

so i still really dont get summary route...so is summary classless.....or classful....and so like on my ccna book is say that classful network will exchange between foregin network..so does that mean let say you have a router A with

192.168.5.0 /24
192.168.6.0/24
192.168.7.0/24

the summary route will be 192.168.4.0/22

and is connected to another router B and the wan between the two router is let say 10.10.0.0/24....that does mean router A will tell router B that it is a 192.168.4.0/22 network instead of 192.168.5.0/24 192.168.6.0/24 192.168.7.0/24

and one last thing...so in ospf and ripv2 we need to manually summary network since is classless...is that right?