What is the difference between CIDR and VLSM ?
In CIDR , an IP network is represented by a prefix, which is an IP address and some indication of the length of the mask. Length means the number of left-most contiguous mask bits that are set to one. So network 172.16.0.0 255.255.0.0 can be represented as 172.16.0.0/16. CIDR also depicts a more hierarchical Internet architecture, where each domain takes its IP addresses from a higher level. This allows for the summarization of the domains to be done at the higher level. For example, if an ISP owns network 172.16.0.0/16, then the ISP can offer 172.16.1.0/24, 172.16.2.0/24, and so on to customers. Yet, when advertising to other providers, the ISP only needs to advertise 172.16.0.0/16.
Variable Length Subnet Masks (VLSM) allows you to use different masks for each subnet, thereby using address space efficiently.
Given the same network and requirements as in Sample Exercise 2 develop a subnetting scheme with the use of VLSM, given:
netA: must support 14 hosts
netB: must support 28 hosts
netC: must support 2 hosts
netD: must support 7 hosts
netE: must support 28 host
so the difference is CIDR is supernetting while VLSM is explained better with the following:
126.96.36.199 can be broken down into 5 different networks given the example requirement above into:
netB: 188.8.131.52/27 host address range 1 to 30
netE: 184.108.40.206/27 host address range 33 to 62
netA: 220.127.116.11/28 host address range 65 to 78
netD: 18.104.22.168/28 host address range 81 to 94
netC: 22.214.171.124/30 host address range 97 to 98
Clear as mud?