{"id":4429,"date":"2014-02-06T21:06:15","date_gmt":"2014-02-06T21:06:15","guid":{"rendered":"http:\/\/www.wikisee.info\/?p=4429"},"modified":"2016-08-09T12:07:06","modified_gmt":"2016-08-09T12:07:06","slug":"difference-between-cidr-and-vlsm","status":"publish","type":"post","link":"https:\/\/wiki-see.info\/wp\/2014\/02\/06\/difference-between-cidr-and-vlsm\/","title":{"rendered":"Difference between CIDR and VLSM?"},"content":{"rendered":"

Classless Inter-Domain Routing\u00a0is based on\u00a0variable-length subnet masking<\/strong>.<\/p>\n

CIDR<\/span> and VLSM<\/span> both allow a portion of the IP address space to be recursively divided into subsequently smaller pieces. The difference is\u00a0<\/span>that with VLSM<\/span>, the recursion is performed on the address space previously assigned to an organization and is invisible to the global Internet. CIDR<\/span>, on the other hand, permits the recursive allocation of an address block by an Internet\u00a0Registry<\/span><\/a>\u00a0to a high-level ISP, a mid-level ISP, a low-level ISP, and a private organization\u2019s network.\u00a0<\/span><\/p>\n

In CIDR<\/span> , 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. <\/span><\/p>\n

So network 172.16.0.0 255.255.0.0<\/span> can be represented as 172.16.0.0\/16<\/span>. CIDR<\/span> also depicts a more hierarchical Internet architecture, where each domain takes its IP addresses from a higher level. <\/span><\/p>\n

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<\/span>, then the ISP can offer 172.16.1.0\/24<\/span>, 172.16.2.0\/24<\/span>, and so on to customers. Yet, when advertising to other providers, the ISP only needs to advertise 172.16.0.0\/16<\/span>.<\/span><\/p>\n

Variable Length Subnet Masks (VLSM<\/span>) allows you to use different masks for each subnet, thereby using address space efficiently.<\/span>
\nGiven the same network and requirements as in Sample Exercise 2 develop a subnetting scheme with the use of VLSM, given:<\/span><\/p>\n

netA: must support 14 hosts<\/span><\/em>
\n netB: must support 28 hosts<\/span><\/em>
\n netC: must support 2 hosts<\/span><\/em>
\n netD: must support 7 hosts<\/span><\/em>
\n netE: must support 28 host<\/span><\/em><\/p>\n

so the difference is CIDR<\/span> is supernetting while VLSM<\/span> is explained better with the following:<\/span>
\n204.15.5.0<\/span> can be broken down into 5 different networks given the example requirement above into:<\/span><\/p>\n

netB: 204.15.5.0\/27 host address range 1 to 30<\/span><\/em>
\nnetE: 204.15.5.32\/27 host address range 33 to 62<\/span><\/em>
\nnetA: 204.15.5.64\/28 host address range 65 to 78<\/span><\/em>
\nnetD: 204.15.5.80\/28 host address range 81 to 94<\/span><\/em>
\nnetC: 204.15.5.96\/30 host address range 97 to 98<\/span><\/em><\/p>\n","protected":false},"excerpt":{"rendered":"

Classless Inter-Domain Routing\u00a0is based on\u00a0variable-length subnet masking. CIDR and VLSM both allow a portion of the IP address space to be recursively divided into subsequently smaller pieces. The difference is\u00a0that 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 […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[3],"tags":[146,480,658,725],"class_list":["post-4429","post","type-post","status-publish","format-standard","hentry","category-cisco-routers","tag-cidr","tag-mask","tag-subnet","tag-vlsm"],"_links":{"self":[{"href":"https:\/\/wiki-see.info\/wp\/wp-json\/wp\/v2\/posts\/4429","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/wiki-see.info\/wp\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/wiki-see.info\/wp\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/wiki-see.info\/wp\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/wiki-see.info\/wp\/wp-json\/wp\/v2\/comments?post=4429"}],"version-history":[{"count":1,"href":"https:\/\/wiki-see.info\/wp\/wp-json\/wp\/v2\/posts\/4429\/revisions"}],"predecessor-version":[{"id":4932,"href":"https:\/\/wiki-see.info\/wp\/wp-json\/wp\/v2\/posts\/4429\/revisions\/4932"}],"wp:attachment":[{"href":"https:\/\/wiki-see.info\/wp\/wp-json\/wp\/v2\/media?parent=4429"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/wiki-see.info\/wp\/wp-json\/wp\/v2\/categories?post=4429"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/wiki-see.info\/wp\/wp-json\/wp\/v2\/tags?post=4429"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}