If you have a network and some devices with valid ips configured by either ipv4 local link, apipa, dnssd or zeroconf if you do reboot one of them.

Does the rebooted device get the same ip as before if nothing changes in the network?


Normally it should, according to this IETF draft. However, if for some reason any other device has claimed that address in the meantime, the device must choose a different address.

The automatic address generation needs some randomness, to avoid having all devices choosing the same address (or sequence of addresses). Therefore the mechanism needs a random number generator (RNG). The seed is some device-specific data to initialize the random number generation. A MAC address is a good candidate for this, because it's (supposed to be) unique for every network interface.

  • Hi and thx, i don´t get the part with the seed and the rng. So if nothing has changed the same seed is taken and produces the same number on the host? (like said nothing is changed in the network) – Gobliins Sep 30 '12 at 12:41
  • Basically, yes. Updated my answer with some more explanation. – Ansgar Wiechers Sep 30 '12 at 12:49
  • Ok thx. I try this out soon and will report. – Gobliins Sep 30 '12 at 12:50
  • Like I said: normally they should. It's not guaranteed, though. – Ansgar Wiechers Sep 30 '12 at 12:50
  • 1
    AFAIK both DHCP server and client cache leases, so the client will keep the address, at least as long as it renews the lease before it expires. – Ansgar Wiechers Sep 30 '12 at 13:04

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