Talk:Classless Inter-Domain Routing: Difference between revisions

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==Prefix/suffix==

{{WikiProject banner shell|class=B|

{{WikiProject Computing |importance=mid |network=yes |network-importance=High}}

{{WikiProject Internet |importance=Mid}}

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{{merged-from|CIDR notation|date=2013-03-01}}

{{merged-from|IPv6 subnetting reference|date=2017-08-30}}

{{merged-from|IPv4 subnetting reference|date=2017-09-05}}

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==Confusion==

I'm not quite sure here, but shouldn't "prefix" be replaced with "suffix" instead? --Maik

How in the heck did I interpret 4 minutes as 3 months??!? - [[User:Lucky13pjn|Lucky13pjn]] 19:48, Mar 14, 2005 (UTC)

I think the usual terminology is prefix, since you route packets destined for 193.137.7.30 (for example) through the shortest path to the 193.137.7/24 prefix (which itself is aggregated and reachable through the 193.136/15 prefix (which is composed of the 193.136/16 prefix and the 193.137/16 prefix)).

== External links ==

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There are plenty of online network calculators, and the two ones in the external links are quite limited in functionalities. How about adding [http://www.subnetmask.info/ this one].

--[[User:Olivier Debre|Olivier Debre]] 07:45, 14 April 2006 (UTC)

The term prefix makes sense when you consider how the netmask is expressed in binary [[User:Robertbrockway|Robertbrockway]] 04:40, Apr 18 2005 (UTC)

==Confusion==

How in the heck did I interpret 4 minutes as 3 months??!? - [[User:Lucky13pjn|Lucky13pjn]] 19:48, Mar 14, 2005 (UTC)

==Example==

And how about adding this: [http://vlsm-calc.net/ http://vlsm-calc.net/].

The example about the /22 mask lists a Class-C address (192.168.0.0) but the default mask for Class-C is 255.255.255.0 or /24. I thought that you could only add ones bits to the default mask, not take them away. Wouldn’t a /22 mask have to be associated with a Class-A or B address?

[[User:80.250.189.67|80.250.189.67]]

Both of these are not really CIDR Calculators. A CIDR calculator needs to tell you if your CIDR is valid and then do the expansion and show the mask the range and stuff.

This is the example given:

These two are subneting calculators. The second does not really work. The first would be OK for the subneting article but someone can already see all these tables in the article .

I suggest http://ipduh.com/ip/cidr a calculator actually used by people who use CIDR notation at work. [[User:Tenretnieht|Tenretnieht]] ([[User talk:Tenretnieht|talk]])

:All calculators have since been removed. ~[[User:Kvng|Kvng]] ([[User talk:Kvng|talk]]) 18:48, 20 April 2020 (UTC)

“192.168.0.0 /22 could be written 192.168.0.0 255.255.252.0”

== Refs, history for CIDR Notation? ==

Should it have been something like:

I don't see any refs at all in the section on CIDR Notation. There is also no information about where this notation came from, or where it was first used. It is not used or described in RFC 1518 and RFC 1519, which defined CIDR.

“172.168.0.0 /22 could be written 172.168.0.0 255.255.252.0”

I have heard that [[Phil Karn]] originally came up with the addr/netlength notation as a replacement for the cumbersome addr/dotteddecimalnetmask notation that required manually converting decimal to binary in your head to understand it, but I have no refs for that allegation either. RFC 1878 of December 1995 includes the "CIDR representation form" in a table of network masks, but does not explain the notation. I see that RFC 1918 in February 1996 uses the notation, but does not explain it, and calls previous approaches the "pre-CIDR notation". RFC 1924 from April 1996 describes "standard CIDR address/length notation" but again does not explain it or its history. Similarly RFC 2167 from June 1997 and RFC 2307 from March 1998. So it must have been invented in 1995 or early 1996, but when and by whom?

--[[User:Addnet|addnet]] 18:51, 23 July 2005 (UTC)

The first real *explanation* of CIDR notation in the RFC series is in RFC 2373 of July 1998 -- but that's for IPv6 addresses, not for IPv4 addresses, so not a great ref to use here. Help! [[User:Gnuish|Gnuish]] ([[User talk:Gnuish|talk]]) 13:22, 5 February 2019 (UTC)

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== Host Identifier: Contradictory Claim ==

The restriction on taking bits away from the default mask only applied in the classful networking scheme. Classless routing is just what its name implies — you really don't have any restrictions anymore on what can be done to a "class A" or a "class C" address. With the exception of class D/E, the entire address space is now administered uniformly throughout. So there are no more "classes". Really.

Host identifier is defined as the least significant bits in an IP address following the network prefix bit (which are the most significant bits).

[[User:[e-mail]|[e-mail]]] 06:29, 9 November 2005 (UTC)

"IP addresses are described as consisting of two groups of bits in the address: the most significant bits are the network prefix, which identifies a whole network or subnet, and the least significant set forms the host identifier, which specifies a particular interface of a host on that network."

==Origins of CIDR==

"An IP address is interpreted as composed of two parts: a network-identifying prefix followed by a host identifier within that network."

The first person to suggest using a net-mask to cover a ''group'' of [[classful network]]s (as opposed to subnets of a single classful network) was Carl-Hubert Rokitansky (affectionately known as "Roki" to all :-), in his "Cluster Networking" proposal (which long predated CIDR). (See [http://www.postel.org/pipermail/internet-history/2003-January/000204.html this message] and [http://www.postel.org/pipermail/internet-history/2003-January/000246.html this reply] to the internet-history mailing list.)

"An address was considered to be the combination of an 8, 16, or 24-bit network prefix along with a 24, 16, or 8-bit host identifier respectively."

I had thought for a long time that there were no original documents on line for this proposal; web searches revealed nothing. However, I have just discovered that the [http://www.ietf.org/proceedings/prior29/IETF01.pdf online copy] (''large'' [[Portable Document Format|pdf] file) of the Proceedings of the '1st' IETF (there was actually at least one earlier one) includes a copy of Roki's handwritten slides on the matter, on pp. 45-61 (pdf page numbers). Just noting this here for informational purposes! [[User:Jnc|Noel]] [[User_talk:Jnc|(talk)]] 16:11, 16 September 2005 (UTC)

etc.

Under "CIDR notation" the following is simply confusing, "The IP address is expressed according to the standards of IPv4 or IPv6. The address may denote a single, distinct interface address or the beginning address of an entire network. The aggregation of these bits is often called the host identifier."

This statement goes from talking about an IP address, which includes all the bits, to making the statement that "The aggregation of these bits is often call the host identifier." The way I read that is that all the bits in an IP address aggregated together are called the host identifier. This is obviously at odds with the definition of and other uses of "host identifier".

== Order, Order ==

I like the way you use a notation ie : " ... sixteen contiguous /24 networks ... " which is meaningless until you read later what the / means. Maybe you could assume the reader is new to the ideas of Classless Inter-Domain Routing, which is why he/she came to the page.

In fact, this contradictory sentence about the host identifier seems to be entirely unnecessary for the paragraph to make it's point. Host identifier is already defined, there'e little value in defining it again. [[User:Awisemanwillhear|Awisemanwillhear]] ([[User talk:Awisemanwillhear|talk]]) 19:02, 5 May 2020 (UTC)

Similarly " ... The class, and hence the length of the subnet mask ...", before explaining what a subnet mask is. Very odd. I assume you are writing this for the people who already know it all, and just need a reminder?

:{{ping|Kbrose}} You modified the wording in question on [[Special:Diff/670876972|July 2015]] resulting in {{tq|The aggregation of these bits is often called the ''host identifier''}}. Perhaps that sentence should be removed? [[User:Johnuniq|Johnuniq]] ([[User talk:Johnuniq|talk]]) 00:22, 6 May 2020 (UTC)

::Comparing the diff you presented with the current, indeed faulty text reveals that someone else must have jumbled the text later without reading everything for coherence. I reverted to previous prose with some copyediting. [[User:Kbrose|Kbrose]] ([[User talk:Kbrose|talk]]) 00:40, 6 May 2020 (UTC)

:::Thanks, I'm thinking about code at the moment and didn't really absorb what was going on here. [[User:Johnuniq|Johnuniq]] ([[User talk:Johnuniq|talk]]) 01:50, 6 May 2020 (UTC)

== RFC links ==

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RFC links seems broken? <!-- Template:Unsigned --><span class="autosigned" style="font-size:85%;">—&nbsp;Preceding [[Wikipedia:Signatures|unsigned]] comment added by [[User:XP 2600|XP 2600]] ([[User talk:XP 2600#top|talk]] • [[Special:Contributions/XP 2600|contribs]]) 23:26, 21 July 2021 (UTC)</span>

:{{ping|XP 2600}} Please quote some text from the article that we can search for to identify which link has a problem. This example seems to work: {{IETF RFC|1518}}. By the way, click "new section" (might be "+" for you) at the top of the page to start a new topic. [[User:Johnuniq|Johnuniq]] ([[User talk:Johnuniq|talk]]) 02:38, 22 July 2021 (UTC)

::Thank you!, and sorry for late reply! [[User:XP 2600|XP_2600]] ([[User talk:XP 2600|talk]]) 10:52, 7 August 2024 (UTC)

== internet history timeline ==

Point taken. I think it's better now.

internet history timeline at top of page does nothing to contribute to this article other than take up too much space [[Special:Contributions/67.183.216.182|67.183.216.182]] ([[User talk:67.183.216.182|talk]]) 05:56, 3 October 2024 (UTC)

[[User:[e-mail]|[e-mail]]] 06:30, 9 November 2005 (UTC)