Understanding Windows multiple IPv6 private addresses
i'm learning IPv6 so i was looking at the output of the ipconfig /all command on my pc. I have already disabled the IPv6 temporary address feature in order to avoid the many lines about these addresses.
My output looks like this (real values replaced with xxxx):
Scheda Ethernet Ethernet:
Suffisso DNS specifico per connessione: homenet.telecomitalia.it
Descrizione . . . . . . . . . . . . . : Realtek PCIe GBE Family Controller
Indirizzo fisico. . . . . . . . . . . : xx-xx-xx-xx-xx-xx
DHCP abilitato. . . . . . . . . . . . : Sì
Configurazione automatica abilitata : Sì
Indirizzo IPv6 . . . . . . . . . . . . . . . . . : fd0c:2759:291d:0:xxxx:xxxx:xxxx:xxxx(Preferenziale)
Indirizzo IPv6 . . . . . . . . . . . . . . . . . : fd5a:dde5:fb8c::xxxx(Preferenziale)
Lease ottenuto. . . . . . . . . . . . : lunedì 23 ottobre 2017 15:07:32
Scadenza lease . . . . . . . . . . . : giovedì 29 novembre 2153 22:18:02
Indirizzo IPv6 . . . . . . . . . . . . . . . . . : fd5a:dde5:fb8c:0:xxxx:xxxx:xxxx:xxxx(Preferenziale)
Indirizzo IPv6 locale rispetto al collegamento . : fe80::6c1c:7033:c528:fd5a%10(Preferenziale)
Indirizzo IPv4. . . . . . . . . . . . : 192.168.1.68(Preferenziale)
Subnet mask . . . . . . . . . . . . . : 255.255.255.0
Lease ottenuto. . . . . . . . . . . . : lunedì 23 ottobre 2017 15:07:31
Scadenza lease . . . . . . . . . . . : lunedì 23 ottobre 2017 21:07:30
Gateway predefinito . . . . . . . . . : 192.168.1.1
Server DHCP . . . . . . . . . . . . . : 192.168.1.1
IAID DHCPv6 . . . . . . . . . . . : 55633225
DUID Client DHCPv6. . . . . . . . : 00-01-00-01-1F-88-7C-3A-50-E5-49-CA-EE-F7
Server DNS . . . . . . . . . . . . . : fe80::c66e:1fff:fea2:c01c%10 8.8.8.8 8.8.4.4
NetBIOS su TCP/IP . . . . . . . . . . : AttivatoI do not understand why i have multiple private IPv6 addresses. I mean clearly the one starting with fe80 is a link local address so it's ok but i have 3 other addresses that look like private. The 1st one beginning with fd0c and the 3rd starting with fd5a have the same interface ID, the 2nd begins with fd5a but the interface ID is totally different.
Why should i have multiple private IPv6 addresses on a single interface? Is this something normal? How are they generated if the Interface ID is not the same in all 3 addresses?
51 Answer
If the only public address i have is the one on the modem and it is an ipv4 address, how can i communicate outside of my link using ipv6 addresses?
Because your internet provider does NAT (network address translation) in some way, just like your router does NAT with the 192.168.1.68 private address.
Your router rewrites IPv4 packets coming from this address with a different address (a public IPv4 address, or more likely a provider local address that then again gets NATed by the provider).
In the same way, your internet provider rewrites packets coming from at least one of those three IPv6 addresses, and send them out to the internet with a global IPv6 address. When answering packets arrive, it reverses this process.
If you try to visit some website that lists your public IPv6 address, e.g. this one, you should be able to see the result of the NAT (i.e., some address starting with 2 instead of F).
Why do i have 4 of them and not just 1?
It's completely normal to have multiple IPv6 addresses on one interface. Every interface with IPv6 is required to have a link-local FE80 address, and there's an algorithm that defines which address of those multiple addresses to use as source address.
However, many internet providers just assign a single additional global address.
As to why you have 3 ULA address from your internet provider, I repeat: Only Telecom Italia will be able to tell you, unless someone has figured out the details of the NAT scheme they use. I'm sure they have a reason for it, whatever it may be.
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