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This article currently contains strange paragraphs like
Which is, of course, completely false in the general sense. Has the author not heard of IPv6 for example?
... which raises this question: Should this article really have anything to do with specific protocols, or should it just be an explanation of the term subnetwork with pointers to specific articles about IPv4 subnetting etc? We already have the IPv4 subnetting reference so that seems logical to me.
I would understand links to specific articles from here (such as one for IPv4 subnetworks and another for IPv6 subnetworks), but this seems a bit illogical. How about lifting protocol-specific material out to the revelant articles and pointing to them?
When e.g. IPv6 becomes more common, we'd otherwise have to include that one here as well to be consistent. It's of course another option, but again, we already have a specific IPv4 article for this -- why not use it better? Just a thought. :-) Jugalator 18:39, Aug 21, 2004 (UTC)
In
shouldn't the last eight digits be all zero?
Snip 14:11, 9 September 2005 (UTC)
Putting this here as data for anyone who cares:
The first mention of subnets, in the sense of subdivisions of a classful network, that I know of in Internet documentation occurs in IEN-82, "LCS Net Address Format", from February, 1979. (MIT was using subnets some years before anyone else.) This subnetting scheme, as eventually adopted by the Internet, was more fully described by Jeff Mogul in RFC 917, "Internet subnets", in October 1984.
The notion of subnet masks has to be credited to Dave Moon, though, I think. Although the early LNI hardware supported masks, we didn't really think of using them in the protocol; it was Dave Moon, at an early meeting on an otherwise forgotten piece of technogical detritus named 'MUPPETS' (the name is a play on PARC Universal Packet) - an attempt to deal with the multiplicity of protocol suites inside MIT at the time - who made the mask suggestion at the protocol level, and it was carried forward to Mogul's paper. Noel (talk) 17:52, 19 September 2005 (UTC)
In the example of the chapter "subnetworking concept" it says:
"Determining the number of hosts and subnets on a particular network is quite easy, if you know the subnet mask. Say you have the network address 154.4.32.0 with a subnet mask of 255.255.224.0. This network address can also be written as 154.4.32.0/19
Network address 154.4.32.0 (decimal) => 10011010.00000100.00100000.00000000 (binary) Subnet mask 255.255.224.0 (decimal) => 11111111.11111111.11100000.00000000 (binary) The subnet mask has 19 bits for the network portion of the address, and 13 bits for the host part.
213 = 8192 possible subnets available according to RFC 1812, otherwise using the old RFC 950 standard the number of usable subnets is 6. This is due to RFC 950 (section 2.1, page 5) not supporting subnets with either all 1s or all 0s."
Shouldn't this be 219? - Otherwise, an explanation of why a mask of 19 bits only gives us 213 possible subnets would be nice. (Admitted - I did not read the RFC's, which is also why I didn't just start editing the article on my own, but I think, this explanation goes against a basic sense of math...? —Preceding
unsigned comment added by
62.107.132.247 (
talk •
contribs) 18:46, 11 July 2006
Why ? I mean, why 3? Should we assume this is a class B (/16) network, and we're trying to fit that many /19 in it? So ?—The preceding
unsigned comment was added by
82.238.35.175 (
talk •
contribs) 20:47, October 22, 2006.
The current article says that The 127.0.0.1 Network ID is left out because it is designated for loopback and cannot be assigned to a network. Are there really not more reasons to be mentioned here? It looks very inefficient to take out 224 IP-adresses, and then use only one of them. Bob.v.R 09:03, 15 May 2006 (UTC)
A graphic representation of relationships and source of the various variables representing a chunk of C subnets
"chunk" is an unprofessional term being used here, and that wording is confusing for someone who doesn't already understand subnets, IPv4 and all the terms associated with it. Referring to it as Class C makes it more clear what is being talked about. The other wording:
A graphic representation of the possible lengths of subnets in a class C network
Is a more accurate and concise description of what it is. They are indeed possible lengths, its possible you could have a subnet mask of any of those lengths in a class C network. It will certainly be one of them, but it its possible to be any of them. The image is certainly educational, which is why I didn't remove it, but it needs to be described better.-- Crossmr 16:56, 30 November 2006 (UTC)
In relation to the http://en.wikipedia.org/?title=Subnetwork&diff=91277922&oldid=91271869 edit , i agree with moving the image but otherwise please do not edit my edits anymore , concerning your stated reason for censoring my last edit the data was allready stated , which is false , not once does network address translation is mentioned.
I am in the process to rewrite this article in concordance with the Wikipedia:WikiProject_Computer_networking guidelines , and i was pointing out the history of subnets (reasons why it exists , alternatives) data that need to be in the header
Please comment on the talk page next time you have a issue about my edits not censor them.-- Mancini 15:11, 1 December 2006 (UTC)
I don't see the point of a merge here unless its to make the CIDR article huge. I could only see it being merged to have someone suggest that it be split up because both pieces are quite lengthy.-- Crossmr 02:31, 4 December 2006 (UTC)
Several people have been expressing concern that this was hard to understand. I've spent the last 90 minutes rewriting this article in, what I hope, an easier to understand method. I included some binary examples. I found that when I learned how to subnet seeing it as binary really made things easy for me to understand and grasp the concept. I've only copy edited it a small amount, so I'm sure it does require some of that. I've kept the links as I didn't have the time right now to go through them and make sure they all apply and I've kept a few of the paragraphs and one of the tables that was there before. I've tried to lay down a foundation of what a subnet mask is, what a network address is and how they work together. Any comments are welcome.-- Crossmr 17:47, 28 November 2006 (UTC)
Currently, the article has the following table:
Class | Leading bits | Start | End | Default Subnet Mask in dotted decimal | CIDR notation |
---|---|---|---|---|---|
A | 0 | 0-127.x.x.x | 126.255.255.255 | 255.0.0.0 | /8 |
B | 10 | 128-191.x.x.x | 191.255.255.255 | 255.255.0.0 | /16 |
C | 110 | 192-223.x.x.x | 223.255.255.255 | 255.255.255.0 | /24 |
D | 1110 | 224-239.x.x.x | 239.255.255.255 | ||
E | 1111 | 240-255.x.x.x | 255.255.255.0 |
Shouldn't it be 0-126.x.x.x in the field Start | A? -- Abdull 17:23, 10 April 2007 (UTC)
I consider myself fairly technically savvy, but I’m no network admin. I found this article is highly technical and presents more theory rather then explanations. I might suggest it’s a challenging for anyone to understand this who doesn't already have an extensive knoweldge of networking terminology. I found the external link to the about.com article far more effective at describing what subnetworking really is with better examples. -- Trode 18:31, 1 December 2005 (UTC)
i added a "simplify" tag for the reasons stated here—The preceding unsigned comment was added by 165.173.14.76 ( talk • contribs) 01:30, December 14, 2006.
Is there a typo under the 'Private subnets' subtitle? When you borrow 2 bits and examine the networks, shouldn't you get 192.168.1.0, .64, .128 and .192 networks only? .0 being all zeros and .192 being all ones taking those out. Then the theory behind calculating the amount of networks you get would match also (2^2-2 = 2).
It would be useful to find on this page something defining the format of a subnet mask. What I've not found is: subnet mask can be only in the format 1...10...0 or can zeros be also inside 1s part?
I deleted some stuff earlier from the page (end of Subnets and host count, after 2nd table), which subsequently got added back in (along with some constructive additions). I still think the portion significantly detracts from the article, but rather than end up in an edit war I'll just put my thoughts here and leave it up to someone else to decide.
Firstly the section was surrounded with comment tags, some of which were nested meaning that only part of the text was rendered (about 50% was just a waste of bandwidth). What is left is a rambling rehash of earlier parts of the article, including parts where the author has added '???' to show they aren't sure what is happening and sections highlighted in bold for no apparent reason.
If anyone can see any redeeming information in this portion it would be useful if they could reformat it and move to the relevant sections of the article. Tjpayne 20:19, 24 July 2007 (UTC)
I propose that IPv4 subnetting reference be merged into this. There's redundant information, and the other article seems very incomplete. —Preceding unsigned comment added by Reinderien ( talk • contribs) 02:36, 11 June 2008 (UTC)
I disagree. If any merge is to be done, sections of this page should be merged into IPv4 subnetting reference. The title is more descriptive, and the information is more detailed than on this page. NetworkFloridaDOTcom ( talk) 15:26, 24 October 2008 (UTC)
I disagree. This page is strictly about IPv4 addressing, whereas the Subnet article should discuss subnetting in all versions of IP. I will remove the template, since this has been posted for some time. Kbrose ( talk) 21:35, 31 October 2008 (UTC)
Are the changes made in this 31 Dec 2008 edit http://en.wikipedia.org/?title=Subnetwork&diff=261020601&oldid=260259765 really an improvement? Seems to be a fair bit of material deleted and the opening sentence seems worse. However I do not have the knowledge to know for sure. Nurg ( talk) 23:10, 14 January 2009 (UTC)
Please move the example with the cable modem near the bottom of the article to be near the top, its the clearest explanation of the concept across the whole article. If a diagram illustrating the relationships could be added that would really make it clear! —Preceding unsigned comment added by 65.91.42.118 ( talk) 14:23, 7 May 2009 (UTC)
From the standpoint of a Wikipedia reader (and not an editor), it would make sense that one of the more common subnet mask addresses lead here. For example, I typed in 192.168.1.1 and it lead to the localhost article. Should 255.255.255.0 similarly be redirected here? I would do it myself but I have no idea how to do it. Thanks for reading —Preceding unsigned comment added by 207.255.210.182 ( talk) 14:24, 10 May 2009 (UTC)
I see the logic, and it seams like a sensible idea. But then the question comes up "where do you see 255.255.255.0 and not be told it is a subnet mask?" As for the example you gave, I could see 127.0.0.1 redirecting to localhost, but shouldn't 192.168.1.1 either to default gateway or more likely the article focusing on private addresses? But I'm no editor, a poor writer, an just use Wikipedia anon. 97.122.165.186 ( talk) 22:29, 31 July 2009 (UTC)
I came to the page looking for answers and information for implementing subnets, this page didn't really help. While it may be very useful in some categories, and KUDOS to those editing it, it is missing a section on how to implement subnets. Sure subnets are useful, here is what they are useful for, here are some changes occurring in the networking space, etc. Where is the implementation section? How to use a subnet. Think of your audience as technically inclined individuals who are trying to set up home networks, or office networks that don't feel like calling the cable guy. eximo ( talk) 22:22, 12 October 2009 (UTC)
per request. Not suitably reference (only 4 at the time of writing!). Airplaneman talk 05:14, 14 November 2009 (UTC)
Whoever wrote up the total useable hosts bit is smoking crack. Someone please fix this so I dont have to find some other random article on subnet masks to show people who dont know what subnetting is. I'll let a wiki savvy person do that, but I wanted to point out this serious fundimental error. -- 64.69.87.237 ( talk) 07:06, 7 January 2010 (UTC)
To me it sort of seems to be the other way around, since each device needs one adress in each subnett it is a part of. So subnetting means that routers needs more adresses. In addition each subnett must have a power of two adresses, so some adresses will be unused. It would seem to me to be more efficient, in terms of adress use, to not subnett at all, although this would make routing a nightmare. So in conclusion, isn't the reason for subnetting facilitation efficient routing, rather than saving adresses? 213.161.190.227 ( talk) 05:41, 28 April 2010 (UTC)
This article is way too confusing and haphazard. A far better and to-the-point explanation about subnets and masks and what those numbers mean is here: http://www.iplocation.net/tools/netmask.php — Preceding unsigned comment added by 24.22.219.163 ( talk) 12:01, 23 July 2012 (UTC)
I'm not going to make the edit in the article for fear of not being clear enough. :) But I will add it here.
What might help people is seeing how the bits get added up. Everything progresses rather logically when you look at it in binary but it's the translation to decimal that makes everything look so random.
Bit 1 | Bit 2 | Bit 3 | Bit 4 | Bit 5 | Bit 6 | Bit 7 | Bit 8 |
---|---|---|---|---|---|---|---|
0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
128 | 64 | 32 | 16 | 8 | 4 | 2 | 1 |
With no bits selected, the value is 0.
Bit 1 | Bit 2 | Bit 3 | Bit 4 | Bit 5 | Bit 6 | Bit 7 | Bit 8 |
---|---|---|---|---|---|---|---|
1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
128 | 64 | 32 | 16 | 8 | 4 | 2 | 1 |
1+2+4+8+16+32+64+128=255
Bit 1 | Bit 2 | Bit 3 | Bit 4 | Bit 5 | Bit 6 | Bit 7 | Bit 8 |
---|---|---|---|---|---|---|---|
1 | 1 | 0 | 0 | 0 | 0 | 0 | 0 |
128 | 64 | 32 | 16 | 8 | 4 | 2 | 1 |
128+64=192
This should make the whole idea of borrowing bits here and there more sensible.
-- Gmuir 13:40, 17 May 2007 (UTC)
EMBOH ORA WERO AQ — Preceding unsigned comment added by 114.79.48.34 ( talk) 05:32, 15 December 2012 (UTC)
"When Foo sends data to example.com at 208.77.188.166, the router performs a logical AND of the destination example.com address with the subnet mask. It also performs a logical AND of the origin address (17.76.99.1) and recognizes that these two results are different, and therefore sends the data over the Internet, via the subnet's default gateway." "It also performs a logical AND of the origin address (17.76.99.1)" It performs a logical AND with the origin address and what? AND operations involve two cases. It would also help to have the binary code stacked on top of eachother so you do the AND operation for yourself in your head more easily. 173.70.15.67 ( talk) 14:24, 13 September 2009 (UTC)flat9@hotmail.com
to point out, it's not a LOGICAL AND, its a BITWISE AND. logical and is eg. if(1>2 && 2<3) while bitwise and would be eg. 3 & 2 = 2 (tus) — Preceding unsigned comment added by 74.84.117.50 ( talk) 18:15, 18 April 2013 (UTC)
"For example, 255.255.255.0 is the network mask for the 192.168.1.0/24 prefix." while this is true, 255.255.255.0 is the network mask for anything that ends in 0. so it's also the mask for 208.33.47.0 a more accurate mask would be 192.168.1.0. applying that mask to anything in the 192.168.1.0/24 range will always yield 192.168.1.0 (so 192.168.1.101 masked with 192.168.1.0 will yield 192.168.1.0 but 208.33.47.0 masked to 192.168.1.0 will yield 208.33.47.0 and thus not be routed with this mask — Preceding unsigned comment added by 74.84.117.50 ( talk) 18:35, 18 April 2013 (UTC)
As far as I know, the term "subnetting" has no formal meaning since the introduction of CIDR. The term "subnetwork" is sometimes used as a synonym for "network" but no longer have a formal meaning either.
The process of subnetting was the process of splitting a Class A, B or C network into multiples subnetworks. It can be seen as the ancestor of CIDR. It used the concept of subnet mask which was later re-used by CIDR in a slightly different way and notation. Since the network classes no longer exist because CIDR was introduced, there is no more such a thing as "subnetting".
The article is very misleading as it try to explain the concept of subnetting without specifying that it is an outdated concept and while using newer concept that didn't existed at the times subnetting was used.
I don't have the time and the motivation to fix the article but here is some tip to correct/understand it:
Pyrrhonist05 ( talk) 15:53, 6 August 2017 (UTC)
While in IPv6 the prefix must consist of a set of contiguous 1-bits, in IPv4 this is not enforced
As noted under "Routing prefix" above, the article is still (or once more) inconsistent in its terminology. The intro now refers to "the network number or routing prefix" but the diagram uses network identifier and the later tables refer to network prefix. I don't have the subject expertise (or, it appears, the Inkscape expertise – see File:Subnetting Concept-en.svg) to fix it. Dave.Dunford ( talk) 13:51, 16 February 2019 (UTC)
This was referred to as network number, routing prefix and network prefix. For consistency and clarity, I've changed all to routing prefix (and prefix for short) because that's what was predominantly used in the article. We probably want to go with the term used predominantly in the literature. I'm thinking that's network number but I'd like to solicit opinitions and citations on this. -- Kvng ( talk) 21:15, 4 October 2010 (UTC)
This sentence appears wrong to me: "The recommended allocation for an IPv6 customer site is an address space with an 80-bit (/48) prefix". I think it should be 80 bit suffix. The referenced page (ref 16 - getipv6.info) says: "No subnets will use prefixes longer than /64. " which to me says the maximum prefix length is 64 bits. — Preceding
unsigned comment added by
209.228.188.200 (
talk) 11:37, 5 March 2012 (UTC)
It is still impossible, by reading this article, to understand what a subnet mask is (beyond (in IPv4 at least) the fact that it is a 32 bit number) and what it actually does. This confusion may be caused by trying to relate what is written here to many (most?) people's experience of a subnet mask as being a mysterious dotted quad in their Windows network adapter's configuration which seems to serve no purpose (I can set mine to any acceptable number greater or equal to 254 and everything still works), and is never explained in MS help.
It would help if there could be some explanation of what the subnet mask actually does on a single system using an IP address exclusively?
What does it do if you have a single internet connection and, say, 6 computers attached to a router?
In which pieces of equipment is the mask actually used and what does it do in each?
I have a suspicion that this is one of those articles that makes perfect sense if you already know what a subnet mask is but is absolutely opaque if you don't. PRL42 ( talk) 17:10, 30 June 2014 (UTC)
This article needs a lot of improvement. It states the same common simple basics, and leaves unclear the crucial practical implications.
My current understanding is this: each network device starts with a MAC address and sooner or later has an IP address and a subnet mask. Ordinarily the subnet mask would be configured to be consistent with all the other locally directly connected devices; if not, the situation is complicated and confusing. But in the simple ordinary case, the subnet masks will all be consistent within the local network. Each time each device wants to initiate a communication, it uses the subnet mask to calculate whether the other party it wants to reach is in the same subnet. If it thinks so, it uses a simple set of local methods to communicate rather directly. But if it thinks the other party is not in the same subnet, then it will try to use completely different indirect methods, by reaching out to a gateway etc in hopes of eventually reaching the desired party. This seems to be the key practical significance of subnet masks. If this is true, the article should clearly convey this key significance.
It may also be that within subnets most communications are by ARP MAC and between subnets most by IP, which is pretty simple and important to understand and worth stating in the article, if so. - 71.174.178.251 ( talk) 18:08, 4 July 2014 (UTC)
When was subnet addressing added to IPv4? We should probably also say when CIDR was added. I almost remember before subnets, but not close enough. Gah4 ( talk) 06:15, 9 September 2021 (UTC)
I'm a little concerned that third-party Cisco certification preparation guides are being listed, here and in other networking articles, as references seemingly at the same level of authority as RFCs and even vendor-independent texts. From personal experience both as a Cisco instructor and in the preparation of certification preparation material, these sometimes differ from such things as the primary standard, because the author(s) understand that the certification tests are usually based on Cisco courseware, which sometimes has obsolete or proprietary material. This is not to say that the certification guides aren't accurate for the purpose, but they aren't definitive for the field.
When RFCs from the IETF address the subject, especially if they are Standards Track, they are authoritative. Now, with all proper disclaimers, I have written vendor-independent networking books, such as Designing Addresing Architectures for Routing and Switching from MacMillan. Other authors also have written books that were not strictly written for Cisco purposes. I have also written certification study aids at certificationzone.com, and I would consider the vendor-independent material more definitive. In some of the study aids for which I was responsible, the authors would point out there is a "right way, a wrong way, and a Cisco way." Bottom line: if an RFC speaks to a subject, it should be considered definitive unless there is overwhelming evidence to the contrary, or it is superceded by another RFC. Howard C. Berkowitz 13:20, 19 July 2007 (UTC)
![]() | This page is an archive of past discussions. Do not edit the contents of this page. If you wish to start a new discussion or revive an old one, please do so on the current talk page. |
This article currently contains strange paragraphs like
Which is, of course, completely false in the general sense. Has the author not heard of IPv6 for example?
... which raises this question: Should this article really have anything to do with specific protocols, or should it just be an explanation of the term subnetwork with pointers to specific articles about IPv4 subnetting etc? We already have the IPv4 subnetting reference so that seems logical to me.
I would understand links to specific articles from here (such as one for IPv4 subnetworks and another for IPv6 subnetworks), but this seems a bit illogical. How about lifting protocol-specific material out to the revelant articles and pointing to them?
When e.g. IPv6 becomes more common, we'd otherwise have to include that one here as well to be consistent. It's of course another option, but again, we already have a specific IPv4 article for this -- why not use it better? Just a thought. :-) Jugalator 18:39, Aug 21, 2004 (UTC)
In
shouldn't the last eight digits be all zero?
Snip 14:11, 9 September 2005 (UTC)
Putting this here as data for anyone who cares:
The first mention of subnets, in the sense of subdivisions of a classful network, that I know of in Internet documentation occurs in IEN-82, "LCS Net Address Format", from February, 1979. (MIT was using subnets some years before anyone else.) This subnetting scheme, as eventually adopted by the Internet, was more fully described by Jeff Mogul in RFC 917, "Internet subnets", in October 1984.
The notion of subnet masks has to be credited to Dave Moon, though, I think. Although the early LNI hardware supported masks, we didn't really think of using them in the protocol; it was Dave Moon, at an early meeting on an otherwise forgotten piece of technogical detritus named 'MUPPETS' (the name is a play on PARC Universal Packet) - an attempt to deal with the multiplicity of protocol suites inside MIT at the time - who made the mask suggestion at the protocol level, and it was carried forward to Mogul's paper. Noel (talk) 17:52, 19 September 2005 (UTC)
In the example of the chapter "subnetworking concept" it says:
"Determining the number of hosts and subnets on a particular network is quite easy, if you know the subnet mask. Say you have the network address 154.4.32.0 with a subnet mask of 255.255.224.0. This network address can also be written as 154.4.32.0/19
Network address 154.4.32.0 (decimal) => 10011010.00000100.00100000.00000000 (binary) Subnet mask 255.255.224.0 (decimal) => 11111111.11111111.11100000.00000000 (binary) The subnet mask has 19 bits for the network portion of the address, and 13 bits for the host part.
213 = 8192 possible subnets available according to RFC 1812, otherwise using the old RFC 950 standard the number of usable subnets is 6. This is due to RFC 950 (section 2.1, page 5) not supporting subnets with either all 1s or all 0s."
Shouldn't this be 219? - Otherwise, an explanation of why a mask of 19 bits only gives us 213 possible subnets would be nice. (Admitted - I did not read the RFC's, which is also why I didn't just start editing the article on my own, but I think, this explanation goes against a basic sense of math...? —Preceding
unsigned comment added by
62.107.132.247 (
talk •
contribs) 18:46, 11 July 2006
Why ? I mean, why 3? Should we assume this is a class B (/16) network, and we're trying to fit that many /19 in it? So ?—The preceding
unsigned comment was added by
82.238.35.175 (
talk •
contribs) 20:47, October 22, 2006.
The current article says that The 127.0.0.1 Network ID is left out because it is designated for loopback and cannot be assigned to a network. Are there really not more reasons to be mentioned here? It looks very inefficient to take out 224 IP-adresses, and then use only one of them. Bob.v.R 09:03, 15 May 2006 (UTC)
A graphic representation of relationships and source of the various variables representing a chunk of C subnets
"chunk" is an unprofessional term being used here, and that wording is confusing for someone who doesn't already understand subnets, IPv4 and all the terms associated with it. Referring to it as Class C makes it more clear what is being talked about. The other wording:
A graphic representation of the possible lengths of subnets in a class C network
Is a more accurate and concise description of what it is. They are indeed possible lengths, its possible you could have a subnet mask of any of those lengths in a class C network. It will certainly be one of them, but it its possible to be any of them. The image is certainly educational, which is why I didn't remove it, but it needs to be described better.-- Crossmr 16:56, 30 November 2006 (UTC)
In relation to the http://en.wikipedia.org/?title=Subnetwork&diff=91277922&oldid=91271869 edit , i agree with moving the image but otherwise please do not edit my edits anymore , concerning your stated reason for censoring my last edit the data was allready stated , which is false , not once does network address translation is mentioned.
I am in the process to rewrite this article in concordance with the Wikipedia:WikiProject_Computer_networking guidelines , and i was pointing out the history of subnets (reasons why it exists , alternatives) data that need to be in the header
Please comment on the talk page next time you have a issue about my edits not censor them.-- Mancini 15:11, 1 December 2006 (UTC)
I don't see the point of a merge here unless its to make the CIDR article huge. I could only see it being merged to have someone suggest that it be split up because both pieces are quite lengthy.-- Crossmr 02:31, 4 December 2006 (UTC)
Several people have been expressing concern that this was hard to understand. I've spent the last 90 minutes rewriting this article in, what I hope, an easier to understand method. I included some binary examples. I found that when I learned how to subnet seeing it as binary really made things easy for me to understand and grasp the concept. I've only copy edited it a small amount, so I'm sure it does require some of that. I've kept the links as I didn't have the time right now to go through them and make sure they all apply and I've kept a few of the paragraphs and one of the tables that was there before. I've tried to lay down a foundation of what a subnet mask is, what a network address is and how they work together. Any comments are welcome.-- Crossmr 17:47, 28 November 2006 (UTC)
Currently, the article has the following table:
Class | Leading bits | Start | End | Default Subnet Mask in dotted decimal | CIDR notation |
---|---|---|---|---|---|
A | 0 | 0-127.x.x.x | 126.255.255.255 | 255.0.0.0 | /8 |
B | 10 | 128-191.x.x.x | 191.255.255.255 | 255.255.0.0 | /16 |
C | 110 | 192-223.x.x.x | 223.255.255.255 | 255.255.255.0 | /24 |
D | 1110 | 224-239.x.x.x | 239.255.255.255 | ||
E | 1111 | 240-255.x.x.x | 255.255.255.0 |
Shouldn't it be 0-126.x.x.x in the field Start | A? -- Abdull 17:23, 10 April 2007 (UTC)
I consider myself fairly technically savvy, but I’m no network admin. I found this article is highly technical and presents more theory rather then explanations. I might suggest it’s a challenging for anyone to understand this who doesn't already have an extensive knoweldge of networking terminology. I found the external link to the about.com article far more effective at describing what subnetworking really is with better examples. -- Trode 18:31, 1 December 2005 (UTC)
i added a "simplify" tag for the reasons stated here—The preceding unsigned comment was added by 165.173.14.76 ( talk • contribs) 01:30, December 14, 2006.
Is there a typo under the 'Private subnets' subtitle? When you borrow 2 bits and examine the networks, shouldn't you get 192.168.1.0, .64, .128 and .192 networks only? .0 being all zeros and .192 being all ones taking those out. Then the theory behind calculating the amount of networks you get would match also (2^2-2 = 2).
It would be useful to find on this page something defining the format of a subnet mask. What I've not found is: subnet mask can be only in the format 1...10...0 or can zeros be also inside 1s part?
I deleted some stuff earlier from the page (end of Subnets and host count, after 2nd table), which subsequently got added back in (along with some constructive additions). I still think the portion significantly detracts from the article, but rather than end up in an edit war I'll just put my thoughts here and leave it up to someone else to decide.
Firstly the section was surrounded with comment tags, some of which were nested meaning that only part of the text was rendered (about 50% was just a waste of bandwidth). What is left is a rambling rehash of earlier parts of the article, including parts where the author has added '???' to show they aren't sure what is happening and sections highlighted in bold for no apparent reason.
If anyone can see any redeeming information in this portion it would be useful if they could reformat it and move to the relevant sections of the article. Tjpayne 20:19, 24 July 2007 (UTC)
I propose that IPv4 subnetting reference be merged into this. There's redundant information, and the other article seems very incomplete. —Preceding unsigned comment added by Reinderien ( talk • contribs) 02:36, 11 June 2008 (UTC)
I disagree. If any merge is to be done, sections of this page should be merged into IPv4 subnetting reference. The title is more descriptive, and the information is more detailed than on this page. NetworkFloridaDOTcom ( talk) 15:26, 24 October 2008 (UTC)
I disagree. This page is strictly about IPv4 addressing, whereas the Subnet article should discuss subnetting in all versions of IP. I will remove the template, since this has been posted for some time. Kbrose ( talk) 21:35, 31 October 2008 (UTC)
Are the changes made in this 31 Dec 2008 edit http://en.wikipedia.org/?title=Subnetwork&diff=261020601&oldid=260259765 really an improvement? Seems to be a fair bit of material deleted and the opening sentence seems worse. However I do not have the knowledge to know for sure. Nurg ( talk) 23:10, 14 January 2009 (UTC)
Please move the example with the cable modem near the bottom of the article to be near the top, its the clearest explanation of the concept across the whole article. If a diagram illustrating the relationships could be added that would really make it clear! —Preceding unsigned comment added by 65.91.42.118 ( talk) 14:23, 7 May 2009 (UTC)
From the standpoint of a Wikipedia reader (and not an editor), it would make sense that one of the more common subnet mask addresses lead here. For example, I typed in 192.168.1.1 and it lead to the localhost article. Should 255.255.255.0 similarly be redirected here? I would do it myself but I have no idea how to do it. Thanks for reading —Preceding unsigned comment added by 207.255.210.182 ( talk) 14:24, 10 May 2009 (UTC)
I see the logic, and it seams like a sensible idea. But then the question comes up "where do you see 255.255.255.0 and not be told it is a subnet mask?" As for the example you gave, I could see 127.0.0.1 redirecting to localhost, but shouldn't 192.168.1.1 either to default gateway or more likely the article focusing on private addresses? But I'm no editor, a poor writer, an just use Wikipedia anon. 97.122.165.186 ( talk) 22:29, 31 July 2009 (UTC)
I came to the page looking for answers and information for implementing subnets, this page didn't really help. While it may be very useful in some categories, and KUDOS to those editing it, it is missing a section on how to implement subnets. Sure subnets are useful, here is what they are useful for, here are some changes occurring in the networking space, etc. Where is the implementation section? How to use a subnet. Think of your audience as technically inclined individuals who are trying to set up home networks, or office networks that don't feel like calling the cable guy. eximo ( talk) 22:22, 12 October 2009 (UTC)
per request. Not suitably reference (only 4 at the time of writing!). Airplaneman talk 05:14, 14 November 2009 (UTC)
Whoever wrote up the total useable hosts bit is smoking crack. Someone please fix this so I dont have to find some other random article on subnet masks to show people who dont know what subnetting is. I'll let a wiki savvy person do that, but I wanted to point out this serious fundimental error. -- 64.69.87.237 ( talk) 07:06, 7 January 2010 (UTC)
To me it sort of seems to be the other way around, since each device needs one adress in each subnett it is a part of. So subnetting means that routers needs more adresses. In addition each subnett must have a power of two adresses, so some adresses will be unused. It would seem to me to be more efficient, in terms of adress use, to not subnett at all, although this would make routing a nightmare. So in conclusion, isn't the reason for subnetting facilitation efficient routing, rather than saving adresses? 213.161.190.227 ( talk) 05:41, 28 April 2010 (UTC)
This article is way too confusing and haphazard. A far better and to-the-point explanation about subnets and masks and what those numbers mean is here: http://www.iplocation.net/tools/netmask.php — Preceding unsigned comment added by 24.22.219.163 ( talk) 12:01, 23 July 2012 (UTC)
I'm not going to make the edit in the article for fear of not being clear enough. :) But I will add it here.
What might help people is seeing how the bits get added up. Everything progresses rather logically when you look at it in binary but it's the translation to decimal that makes everything look so random.
Bit 1 | Bit 2 | Bit 3 | Bit 4 | Bit 5 | Bit 6 | Bit 7 | Bit 8 |
---|---|---|---|---|---|---|---|
0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
128 | 64 | 32 | 16 | 8 | 4 | 2 | 1 |
With no bits selected, the value is 0.
Bit 1 | Bit 2 | Bit 3 | Bit 4 | Bit 5 | Bit 6 | Bit 7 | Bit 8 |
---|---|---|---|---|---|---|---|
1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
128 | 64 | 32 | 16 | 8 | 4 | 2 | 1 |
1+2+4+8+16+32+64+128=255
Bit 1 | Bit 2 | Bit 3 | Bit 4 | Bit 5 | Bit 6 | Bit 7 | Bit 8 |
---|---|---|---|---|---|---|---|
1 | 1 | 0 | 0 | 0 | 0 | 0 | 0 |
128 | 64 | 32 | 16 | 8 | 4 | 2 | 1 |
128+64=192
This should make the whole idea of borrowing bits here and there more sensible.
-- Gmuir 13:40, 17 May 2007 (UTC)
EMBOH ORA WERO AQ — Preceding unsigned comment added by 114.79.48.34 ( talk) 05:32, 15 December 2012 (UTC)
"When Foo sends data to example.com at 208.77.188.166, the router performs a logical AND of the destination example.com address with the subnet mask. It also performs a logical AND of the origin address (17.76.99.1) and recognizes that these two results are different, and therefore sends the data over the Internet, via the subnet's default gateway." "It also performs a logical AND of the origin address (17.76.99.1)" It performs a logical AND with the origin address and what? AND operations involve two cases. It would also help to have the binary code stacked on top of eachother so you do the AND operation for yourself in your head more easily. 173.70.15.67 ( talk) 14:24, 13 September 2009 (UTC)flat9@hotmail.com
to point out, it's not a LOGICAL AND, its a BITWISE AND. logical and is eg. if(1>2 && 2<3) while bitwise and would be eg. 3 & 2 = 2 (tus) — Preceding unsigned comment added by 74.84.117.50 ( talk) 18:15, 18 April 2013 (UTC)
"For example, 255.255.255.0 is the network mask for the 192.168.1.0/24 prefix." while this is true, 255.255.255.0 is the network mask for anything that ends in 0. so it's also the mask for 208.33.47.0 a more accurate mask would be 192.168.1.0. applying that mask to anything in the 192.168.1.0/24 range will always yield 192.168.1.0 (so 192.168.1.101 masked with 192.168.1.0 will yield 192.168.1.0 but 208.33.47.0 masked to 192.168.1.0 will yield 208.33.47.0 and thus not be routed with this mask — Preceding unsigned comment added by 74.84.117.50 ( talk) 18:35, 18 April 2013 (UTC)
As far as I know, the term "subnetting" has no formal meaning since the introduction of CIDR. The term "subnetwork" is sometimes used as a synonym for "network" but no longer have a formal meaning either.
The process of subnetting was the process of splitting a Class A, B or C network into multiples subnetworks. It can be seen as the ancestor of CIDR. It used the concept of subnet mask which was later re-used by CIDR in a slightly different way and notation. Since the network classes no longer exist because CIDR was introduced, there is no more such a thing as "subnetting".
The article is very misleading as it try to explain the concept of subnetting without specifying that it is an outdated concept and while using newer concept that didn't existed at the times subnetting was used.
I don't have the time and the motivation to fix the article but here is some tip to correct/understand it:
Pyrrhonist05 ( talk) 15:53, 6 August 2017 (UTC)
While in IPv6 the prefix must consist of a set of contiguous 1-bits, in IPv4 this is not enforced
As noted under "Routing prefix" above, the article is still (or once more) inconsistent in its terminology. The intro now refers to "the network number or routing prefix" but the diagram uses network identifier and the later tables refer to network prefix. I don't have the subject expertise (or, it appears, the Inkscape expertise – see File:Subnetting Concept-en.svg) to fix it. Dave.Dunford ( talk) 13:51, 16 February 2019 (UTC)
This was referred to as network number, routing prefix and network prefix. For consistency and clarity, I've changed all to routing prefix (and prefix for short) because that's what was predominantly used in the article. We probably want to go with the term used predominantly in the literature. I'm thinking that's network number but I'd like to solicit opinitions and citations on this. -- Kvng ( talk) 21:15, 4 October 2010 (UTC)
This sentence appears wrong to me: "The recommended allocation for an IPv6 customer site is an address space with an 80-bit (/48) prefix". I think it should be 80 bit suffix. The referenced page (ref 16 - getipv6.info) says: "No subnets will use prefixes longer than /64. " which to me says the maximum prefix length is 64 bits. — Preceding
unsigned comment added by
209.228.188.200 (
talk) 11:37, 5 March 2012 (UTC)
It is still impossible, by reading this article, to understand what a subnet mask is (beyond (in IPv4 at least) the fact that it is a 32 bit number) and what it actually does. This confusion may be caused by trying to relate what is written here to many (most?) people's experience of a subnet mask as being a mysterious dotted quad in their Windows network adapter's configuration which seems to serve no purpose (I can set mine to any acceptable number greater or equal to 254 and everything still works), and is never explained in MS help.
It would help if there could be some explanation of what the subnet mask actually does on a single system using an IP address exclusively?
What does it do if you have a single internet connection and, say, 6 computers attached to a router?
In which pieces of equipment is the mask actually used and what does it do in each?
I have a suspicion that this is one of those articles that makes perfect sense if you already know what a subnet mask is but is absolutely opaque if you don't. PRL42 ( talk) 17:10, 30 June 2014 (UTC)
This article needs a lot of improvement. It states the same common simple basics, and leaves unclear the crucial practical implications.
My current understanding is this: each network device starts with a MAC address and sooner or later has an IP address and a subnet mask. Ordinarily the subnet mask would be configured to be consistent with all the other locally directly connected devices; if not, the situation is complicated and confusing. But in the simple ordinary case, the subnet masks will all be consistent within the local network. Each time each device wants to initiate a communication, it uses the subnet mask to calculate whether the other party it wants to reach is in the same subnet. If it thinks so, it uses a simple set of local methods to communicate rather directly. But if it thinks the other party is not in the same subnet, then it will try to use completely different indirect methods, by reaching out to a gateway etc in hopes of eventually reaching the desired party. This seems to be the key practical significance of subnet masks. If this is true, the article should clearly convey this key significance.
It may also be that within subnets most communications are by ARP MAC and between subnets most by IP, which is pretty simple and important to understand and worth stating in the article, if so. - 71.174.178.251 ( talk) 18:08, 4 July 2014 (UTC)
When was subnet addressing added to IPv4? We should probably also say when CIDR was added. I almost remember before subnets, but not close enough. Gah4 ( talk) 06:15, 9 September 2021 (UTC)
I'm a little concerned that third-party Cisco certification preparation guides are being listed, here and in other networking articles, as references seemingly at the same level of authority as RFCs and even vendor-independent texts. From personal experience both as a Cisco instructor and in the preparation of certification preparation material, these sometimes differ from such things as the primary standard, because the author(s) understand that the certification tests are usually based on Cisco courseware, which sometimes has obsolete or proprietary material. This is not to say that the certification guides aren't accurate for the purpose, but they aren't definitive for the field.
When RFCs from the IETF address the subject, especially if they are Standards Track, they are authoritative. Now, with all proper disclaimers, I have written vendor-independent networking books, such as Designing Addresing Architectures for Routing and Switching from MacMillan. Other authors also have written books that were not strictly written for Cisco purposes. I have also written certification study aids at certificationzone.com, and I would consider the vendor-independent material more definitive. In some of the study aids for which I was responsible, the authors would point out there is a "right way, a wrong way, and a Cisco way." Bottom line: if an RFC speaks to a subject, it should be considered definitive unless there is overwhelming evidence to the contrary, or it is superceded by another RFC. Howard C. Berkowitz 13:20, 19 July 2007 (UTC)