CCNA - VLSM vs. CIDR

Author

VLSM vs. CIDR

AndreMCSE

2004-05-15, 10:02 pm

I was going to ask the question what was the difference between VLSM and CIDR, but after reading this http://www.3com.com/other/pdfs/infr...n_US/501302.pdf that I found from a question that was already posted.

From the file:

quote:
CIDR and VLSM both allow a portion of the IP address space to be recursively divided into subsequently smaller pieces. The difference is that with VLSM, the recursion is performed on the address space previously assigned to an organization and is invisible to the global Internet. CIDR, on the other hand, permits the recursive allocation of an address block by an Internet Registry to a high-level ISP, a mid-level ISP, a lowlevel ISP, and a private organization’s network.

Ok what I get form that is that with VLSM the IP address are not on the Internet and CIDR is.

But what is:

quote:
Internet Registry to a high-level ISP, a mid-level ISP, a lowlevel ISP

Well basicly I want some one to translate that whole paragraph for me so I'll understand more about IP addrssing.

Thks in Adv ...

AndreMCSE

2004-05-15, 10:22 pm

Yea one more thing what the heck is the second no. doing the one before and after the () like at the begining there two no. like 232 (4,294,967,296) and 126 (27 -2) ,512 (29)65,536 (216)128K
(131,072)8 = 23, 254 valid host
addresses (28 -2). lastly
16 = 24,

That is all the ones in the file so help me out and please tell what they are.

mikop

2004-05-15, 10:34 pm

think of it as

same thing, but in different scale.

vlsm IS on the internet.

forexample, you are a small business owner who has a T1 line, you have say an estimated need of 80 ip addresses, do the isp give you a whole class C? and with the other half of the class C, is it waiting for another customer who can use it, or can you further make it into smaller networks that can satissfy the need of smaller SOHO customers.

This techniques applies to customers, departments, internal routing etc.

CIDR is the large picture. B4, internet addresses are assigned to organization in large blocks and the distribution is far from balanced. You would find corporations, many now sold to others such as DEC in holding of class A addresses and unwilling to relinquish it. This leave everyone else, like MS with a class B, or an entire continent with a Class A. This is in part why others in the world are so much ahead in moving to ipv6 and US still relatively comfortable with ipv4 + NAT. The trillions of ip mobile phone users in asia and europe aren't very happy with the necessity to have the assignment to be in such a large block. SO ... CIDR address that, boom bye bye class A, now there are more flexibility, instead of 3 choices
/8 /16/ 24, we can assign it base on need/requirement. such as /12 which better distribute and utilize the limited ip addresses.

same coin, different side.

mikop

2004-05-15, 10:58 pm

quote:
Originally posted by AndreMCSE
Y the begining there two no. like 232 (4,294,967,296) and 126 (27 -2) ,512 (29)65,536 (216)128K
(131,072)8 = 23, 254 valid host
addresses (28 -2). lastly
16 = 24,

2^*

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