Talk:IPv4

From Wikipedia, the free encyclopedia

The listed IP addresses no longer point to wikipedia.org - they do point to a Wikimedia Foundation 'wiki does not exist' page however. -- Mithent 17:59, 7 Nov 2004 (UTC)

Contents

[edit] Clarify: Quintillion(Short Scale or long scale?)

The current text specifies a quintillion users to have a set of a quintillion adresses, this is ambiguous since both short scale 1018 or long scale 1030 could be meant. An unclear factor of 1012, if anyone knows how to recalculate the possibilites of addresses, please clarify this. --ananta 11:07, 26 February 2007 (UTC)

[edit] Fragmentation/reassembly confusion

I'm ashamed to admit I don't understand how a reciever knows what order to assemble IP packets in to get the original message.

Looking at the packet summary chart, I see two fields that looks like they could be used for this purpose: Identification and Fragment Offset.

"The next 16-bit field is an identification field. This field is primarily used for uniquely identifying fragments of an original IP datagram."

Another Wikipedia page says datagram = packet. So what's a fragment of an 'original IP packet'? Do you mean 'fragment of the original message'?

"The fragment offset field is 13-bits long, and allows a receiver to determine the place of a particular fragment in the original IP datagram."

Again, same question. And how is this different from the Identification field?

-Carl

When you split a large IP packet up into smaller "fragments" (usually at some router in the middle of the path from the source to the destination), the fragments all look like real IP packets - i.e. they have a full IP header. Almost all the fields will be the same value as in the original packet. (In particular, all the fragments will have the same identification field value.) The differences are:
    • The "total length" field will be smaller - set to the size of each fragment
    • The *more fragments" single bit flag will be one in all but the last fragment
    • The "fragment offset" field will be non-zero in all but the first fragment
Note that at the destination, in any incoming packet, if either:
    • The *more fragments" single bit flag is one, or
    • The "fragment offset" field is non-zero
that packet is a fragment. At the destination, to reassemble the fragments back into the original packet, look for incoming packets with the same value in the id field - they all belong to the same original packet. The offset and total length fields tell you where each piece goes, and how much it fills in. You can tell the total size of the original packet because in the packet with the "more fragments" flag clear, the value of the size field in that packet, plus the value in the offset field (multiplied by 8, IIRC), gives the total length of the original.
Note that you can repeat the fragmentation process (e.g. at a later router) - take a fragment, adjust the offset and total length fields, and create two (or more) new packets. The only complication is that if the "more fragments" flag was zero, set it to one in all but the last fragment. (It's relatively simple programming to write the code so that it doesn't need to know whether the packet it is fragmenting is a fragment, or a complete packet.) Note also that if a packet that was fragmented, and some of the fragments lost, is retransmitted with the same identification number, and also fragmented, fragments from the second copy can be used to fill in the "blank spots" from the first one.
Hope this helps! Now I guess I should cut-n-paste this into the page! :-) Noel 20:38, 21 Oct 2004 (UTC)


1) Is reassembly really done at the destination point ? What about encription down the road on a limited portion of the path, short to the destination ?

2) At the reassembly location, at which level of the IP stack is the reassembly performed ? I understand IP to be a best-effort mechanism which does not react to out-of-order or lost packets ? If the reassembly is not performed at the IP level, how can IP decide to break down a packet, when there is no garantee the transport protocol at the other end implements the reassembly function  ?

Arbiel 16:12, 24 January 2006 (UTC)

1) Yes, the reassembly is (really!) only done at the destination. As far as encryption. If the data is encrypted at the source then it doesn't matter since it will be reassembled at the destination. If a hop in the path is encrypted then it must be decrypted at the end of the hop. Leaving it encrypted would be utterly pointless since neither end knows how to decrypt it.
2) Segmentation and reassembly is always done at the IP layer.
Cburnett 01:19, 22 February 2006 (UTC)


[edit] Fragment offset

In the examples in this article the fragment offset is measured in bytes, however RFC 791 states that fragment offset is measured in groups of 8 bytes (64 bits). In my opinion this article should be updated...

--Patrickdepinguin 18:30, 7 June 2006 (UTC)

I thought so too. So I made it so, almost exactly six months later. :) I was very confused from multiple sources, so I just had to go read the RFC itself, then figured no one else should have to spend all that time...Hope what I wrote is clear.

--Bmpercy 19:16, 7 December 2006 (UTC)

[edit] Right on my PC?

Say if all that fragment gathering happens right on my little PC.

Yes, it does. All RFC-compliant IP hosts perform reassembly. --Brouhaha 02:54, 26 August 2006 (UTC)

[edit] Please dab ECN

In the IPv4#Header diagram, there's a link to ECN, which is a dab page. I'm guessing the link should be to Explicit Congestion Notification, but I'm not sure. Can somebody who knows for sure please fix the link. Thanks -- RoySmith (talk) 15:35, 25 February 2006 (UTC)

It was dab'ed in the table right next to it. :) Cburnett 01:15, 26 February 2006 (UTC)

[edit] Address representations

quote from the article: All/most of these formats should work in all browsers.

Well I'm using Safari 2.0.4 under Mac OS X 10.4.7 and only the Dot-decimal notation brings up a webpage (all the others bring up can't find the server) and even that one's not identical to wikipedia.org - it's a website from wikimedia that reads Wiki does not exist --elias.hc 23:33, 17 July 2006 (UTC)

I haven't researched the correctness of this, but HTTP 1.1 can supply the hostname (en.wikipedia.org) in the request to which the web server can use for virtual domains. I'd be willing to bet that this is what wikipedia uses, which would mean that any thing other than en.wikipedia.org wouldn't be recognized. Cburnett 06:04, 10 December 2006 (UTC)

Request for expansion of this section I came to this page looking for information about just how one specified a range of addresses using the /8, /12, /16, etc notations. Would this be an appropriate section for that information? If so, it would be great if someone added it in. Benthatsme 14:44, 23 May 2007 (UTC)

I'm not quite sure what you mean by a range. Consider, though, that a IPv4 address is 32 bits long. The CIDR notation you use defines the fixed prefix part, so a /8 has 24 bits of subordinate bits, an /12 has 18, and a /16 has /16. The range, therefore, is from the prefix followed, in binary. by all zeroes to the prefix followed by all ones Howard C. Berkowitz 22:51, 15 August 2007 (UTC)

[edit] IP Listing web sites

(Conversation moved from User talk:Corti)

Wondering why you called the link I added yesterday to IPv4 spam? I am a neutral third party (with plenty of WP experience) and I put it there because it seems to be the most inert one out there - I say inert meaning there don't seem to be any ads on it so no real benefit to the recipient (whom I have nothing to do with). I was hoping we could leave that one up so all these annoying .biz (and today .tk) wouldn't be there; it's a neat resource for people who aren't familiar with things like IPs to see what theirs is. — RevRagnarok Talk Contrib 12:23, 8 February 2007 (UTC)

I removed it since it has not encyclopedic value. There is no informational value in fining out one's IP: it gives not information about the concept.Matteo 13:29, 8 February 2007 (UTC)
I disagree. How can finding out someone's own address not be "informational value?" (And no, I'm not being abstract about it like Information Theory classes.) People are adding such links all the time, I think we should have a consensus of a "clean" URL that we can have so that people stop adding "real" spam ones. — RevRagnarok Talk Contrib 13:47, 8 February 2007 (UTC)
I disagree, the page is about IP addresses. The link you provided tell's me nothing about what is an IP. And again it is not clean link: as tons of similar site it supplies a simple info with a lot of advertising.Matteo 13:54, 8 February 2007 (UTC)
All I see on http://www.whatismyip.com/ is a Google search (probably subsidized). At the bottom are two links, one describing WinXP command line stuff (useful), and another explaining IP addresses, a page you seem to be denying. I have nothing to do with the site; if you can come up with one with less BS I would be glad to go with it. — RevRagnarok Talk Contrib 14:45, 8 February 2007 (UTC)
A really clean example would be for example [1] but I'm still not convinced that it belongs to the links list. Let's see if someone else put here his/her opinion ... Matteo 14:49, 8 February 2007 (UTC)
I dont see why you would need to know your IP address via a topic on IPv4... If someone didnt know how/is not clever enough to find their IP address they are not going to be on wiki under the IPv4 section. Just my 2 cents. Tyilin 10:03 16 February 2007 (GMT)


[edit] Reserved addresses

According to RFC3330 we can see, that address 39.0.0.0/8 is no longer reserved, am I right? —Preceding unsigned comment added by 83.21.72.180 (talk • contribs)

Yes, RFC 3330 (I added a space to autolink) states This block therefore no longer has a special use and is subject to allocation to a Regional Internet Registry for assignment in the normal manner. — RevRagnarok Talk Contrib 10:58, 9 April 2007 (UTC)

[edit] class B and x.0.0.0 and x.255.255.255

Name IP address range number of IPs classful description largest CIDR block
24-bit block 10.0.0.0 – 10.255.255.255 16,777,216 single class A 10.0.0.0/8
20-bit block 172.16.0.0 – 172.31.255.255 1,048,576 16 contiguous class Bs 172.16.0.0/12
16-bit block 192.168.0.0 – 192.168.255.255 65,536 256 contiguous class Cs 192.168.0.0/16
16-bit block 169.254.0.0 – 169.254.255.255 65,536 class B 169.254.0.0/16

The 169.254.x.x thing is in class B.... (I'm not very familiar with the subject though so I didn't change it) Also apparently x.0.0.0 and x.255.255.255 mean something so the combinations are only 16,777,214 and 65,534. "The numbers in the host ID cannot all be 255, as this address is used as an IP broadcast address. The host ID cannot be all zeros (0s) because this address is used to denote a network ID." Zephyr103 23:28, 27 August 2007 (UTC)

References to classes is obsolete; special meanings of an last octet of 0 or 255, in any event, have meaning only for Class C addresses. The correct way to interpret special meanings is that the host part of the address (i.e., the part following the prefix) can neither be all binary zeroes or all binary ones. Binary zeroes refer to the subnet as opposed to any host on it, and all-ones is the local broadcast Howard C. Berkowitz 01:24, 29 August 2007 (UTC)

[edit] Deprecation

Anyone know when IPv4 will become fully deprecated? Or when IPv6 will become fully standard? - .:. Jigsy .:. 17:57, 25 September 2007 (UTC)

I doubt anyone can put a date on it. Depending on whose estimate you take, the available IPv4 pool, for new allocations, will be exhausted around 2010. Organizations that can't get their own space may still be able to get space from providers. If they tunnel VPNs through a provider cloud, they should be able to avoid converting for years. To put it in perspective, we've had classless addressing for around 6 years, but how often do you hear people talk about a Class C?
Deprecation will depend, in part, on where you are. The PRC appears to be pushing native IPv6 implementations as IP services become more commonplace. East Asia, generally, is IPv6 friendly. Organizations making new deployments in underserved areas of Latin America and Asia may choose to roll out IPv6 to start, with provisions for tunneling existing deployments.
Obviously, the solidity of host implementations will be a pacing factor, both Microsoft and Linux.
Certain industries also emphasize v6. As I understand, the infrastructure for many 3G and beyond wireless is native IPv6. Aviation seems to be moving that way. Howard C. Berkowitz 18:34, 25 September 2007 (UTC)

[edit] LS(R)R and SS(R)R

In the options area of the article there are two red links for LSRR and SSRR, an article exists for Loose Source Routing: Loose_Source_Routing

Some with more networking experience, should this be linked up? —Preceding unsigned comment added by 139.62.110.70 (talk) 19:24, 23 April 2008 (UTC)