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In IPv4 I am required to have DHCP server or manual config to assign NIC some address.

In IPv6 I found that many machines have some addresses despite the fact I never configured them (moreover, I would like to disable IPv6, but it is resurrecting like a very sticky virus).

This concerns both Windows and Linux.

So, where did they take their addresses?

UPDATE

Addresses are started from fe80::, which is described as "local" in Wikipedia. But I am able to ping this local address of one machine from another one.

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    IPv6 works very differently than IPv4. What have you learned about IPv6 already? Otherwise we might skip some basic info that we assume you know.
    – LPChip
    Apr 12, 2016 at 20:15
  • What makes you think its any different?
    – Ramhound
    Apr 12, 2016 at 20:16
  • Nothing. Please don't explain everything, just answer where they took addresses, I would like to learn in my way :)
    – Dims
    Apr 12, 2016 at 20:16
  • @Ramhound it can't be DHCP, because it is not configured.
    – Dims
    Apr 12, 2016 at 20:17
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    @Ramhound IPv6 adresses will be automatically generated by the OS if no DHCPv6 is present. That is my point regarding making things differently. I guess this also applies for IPv4 giving you a 169.254.x.x address
    – LPChip
    Apr 12, 2016 at 20:22

4 Answers 4

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I believe this and this is the information you're looking for.

It's called Stateless Address Autoconfiguration (SLAAC). Basically IPv6 (unlike IPv4) has autoconfiguration protocols in the absence of a DHCP server built into its design.

In IPv4, if a network adapter is configured for DHCP but no DHCP server responds, it will auto-assign itself an address of 169.254.x.x(/16). This is called a link-local address. Any computer using a link-local address can communicate with other computers using link-local addresses if they are on the same network segment. The key here is that link-local addressing is not a part of the IPv4 spec; it's a de-facto standard popularized by Microsoft.

For IPv6 networks, in addition to the link-local address, you also have SLAAC. In a routed IPv6 infrastructure, routers can supply clients with network info via ICMP the way a DHCP server normally would. And since IPv6 has these protocols built into the spec, any IPv6 router would support these requests from clients if configured to do so.

Also, the IPv6 address space is so incredibly big that clients can randomly assign themselves addresses with little risk of collision with other hosts.

In this way, an entire IPv6 infrastructure could conceivably auto-configure itself entirely without any kind of IP address management system.

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The address start with fe80:: is link-local address .if your system is ipv6 enabled,system will automatically generate this address. It's called Stateless Address Autoconfiguration (SLAAC).For this we dont need any DHCP server.This address Scope is only with in the particular subnet..you cant not access that address from any other subnet.System automatically generating this address from system MAC address.YOU can check this link http://www.tutorialspoint.com/ipv6/ipv6_address_types.htm

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The fe80:: addresses are link-local addresses. Every system automatically configures those on all its interfaces. They are assigned by the system to itself. You can't use them beyond the local link (network, vlan etc) as they are non-routable.

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In IPv4 I am required to have DHCP server or manual config to assign NIC some address.

Almost correct. You either ask for on from a server on the network (DHCP), or statically assign a fixed IP, or run some software which generates an IP in an other way when neither of these are used (e.g. the 169.x.x.x addresses sometimes generates when you do not assign an IP and when a DHCP server is not reachable).

Now IP v6 is more modern, this is not an afterthough, link local communication is build into the protocol from the start. This is different from IPv4. Arguably it is better as long as you are aware of it.


Now to the reason why I am typing an answer while there are already several:

Yes, The fe80:: addresses are local. But not local as in the 127/8 range in IP4. That was local host. There are link local. They are reachable from your local network. It is a minor difference in the text, but quite relevant.

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