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My Windows system got an 169.xx.xx.xx IP address the other day, and I fixed the issue, but why did Microsoft chose this address as the default?

Why not 1.xx.xx.xx or 255.xx.xx.xx? Did one guy at Microsoft say

Hey, pick a number 1 to 255....who just said 169?! OK, we're going with that for our Windows default IP address.

Peter Mortensen
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Adam
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    It's actually not always 169.xx.xx.xx there's also 192.168.xx.xx that I've seen. – James Mertz Jan 27 '11 at 19:28
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    169.xx.xx.xx are very specific in their use and function though and not directly related to the use of the 192.168.xx.xx address schema – Linker3000 Jan 27 '11 at 19:32
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    Yeah, no, KronoS -- you've never seen Windows automatically assign itself a 192.168 IP address... it doesn't do that. – delfuego Jan 28 '11 at 02:35
  • @KronoS - could it be that your router assigned that number to your computer but couldn't obtain an address from the modem, thus not giving you access to the internet? – Adam Jan 28 '11 at 16:18
  • @delfuego you need to put an "@" in front of the name of the person you're trying to respond to... – James Mertz Jan 28 '11 at 16:21
  • @delfuego, @A.Donahue, in my experience 192.168.xx.xx is a very common ip address assignment range, whether coming from a Microsoft server or local router. – James Mertz Jan 28 '11 at 16:26
  • Three [private network](http://en.wikipedia.org/wiki/Private_network) ranges: Class A: 10.0.0.0/8; Class B: 172.16.0.0/12 and Class C: 192.168.0.0/16. – Tamara Wijsman Jan 30 '11 at 02:19
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    @KronoS, you're missing the point. 192.x addresses are *real*. 169.x default addresses mean the computer isn't actually connected to a network. – CarlF Apr 11 '11 at 12:31
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    192.168.0.0/24 has *NOTHING* to do with the reason why 169.254.0.0/24 exists. The ONLY thing they have in common is that they are nonroutable. Stop confusing the two. Windows will never assign itself a 192.168.0.0/24 address. Neither with Microsoft. It always comes from a router or a manual IP assignment. – LawrenceC Jun 18 '12 at 12:55
  • @delfuego can i able to ping the APIPA IP – satheesh91 Sep 03 '14 at 08:07
  • @CarlF incorrect. 169.x means the interface has not received an address from a DHCP server. This may be because the interface is not connected to a network,but it might instead mean that the DHCP server isn't connected, or is malfunctioning. In the latter case they're just as real as 192.x addresses. – Jamie Hanrahan Jul 01 '16 at 14:46

3 Answers3

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It's not MS it is the ISOC ;-)

Have a look at reserved IP address RFC 5735 under special use IPv4: here

169.254.0.0/16 - This is the "link local" block. As described in [RFC3927], it is allocated for communication between hosts on a single link. Hosts obtain these addresses by auto-configuration, such as when a DHCP server cannot be found.

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    I first came across this address space when Apple introduced [Bonjour](http://developer.apple.com/networking/bonjour/specs.html). – Annika Backstrom Jan 28 '11 at 02:38
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    That only defers the description of “why”, though: why did RFC 5735 allocate this specific “magic number” for this use? What’s the rationale? – Konrad Rudolph Jan 28 '11 at 14:13
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    @Konrad - I suspect part of the rationale was that it was available. – Rob Moir Jan 28 '11 at 15:17
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    @Konrad - RFC 5735 is more of a collection of RFC's that pertain to special use netblocks. The actual "meat and potatoes" if you will can be found in RFC 3927 which is linked directly from 5735. As for why the IETF picked this address space for Link local? I can't find the reasoning. –  Jan 28 '11 at 15:47
  • @DanM., What does "link local" mean anyway? How does 192 differ from 169? – Pacerier Nov 12 '17 at 13:44
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The use of 169.x.x.x addresses are defined within a standard colloquially known as APIPA - Automatic Private IP Addressing.

In a nutshell, if a network device has not been assigned a fixed (static) address and cannot obtain one by asking (DHCP), the device says to itself, "Well, I'd better make up an address of my own so I can communicate on this network", so it assigns itself an APIPA address, which start at 169.254.0.1 and run up to 169.254.255.254.

If you suddenly find your computer has an address within the AIPIA range it usually means that the device on the network dishing out addresses (the DHCP server) is not contactable for some reason; it may be switched off or your network cable has become disconnected, for example.

Linker3000
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    Do you mean that once they are able to talk to DHCP, they change from 169 to 192? Is this a standard or is it just by custom? What if he doesn't change even after talking to DHCP? – Pacerier Nov 12 '17 at 13:45
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To state Dan M's answer in another terms, your DHCP server has a problem and cannot allocate an IP address. When Windows and any other OS is configured to get an IP via DHCP and they don't get any, they automatically assign 169.254.xxx.xxx IP

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icasimpan
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