Subj : Birthday present from he.net (some birthday)
To   : Tony Langdon
From : Michiel van der Vlist
Date : Mon Jul 11 2016 01:07:04

Hello Tony,

On Monday July 11 2016 07:35, you wrote to Joe Delahaye:


 TL> Interesting.  But I do know multiple global IPv6 addresses per
 TL> interface is pretty common.

This is one of the big differences between IPv4 and IPv6. Although it is possible to assign more than one Ip addres to an interface, it is far from common, Normally an interface has just one IP address. In IPv6 one has at least two IP adresses. There is always the link local address that starts with fe80::. The lower 64 bits are derived from tha MAC address of the interface. To translate the 48 bit MAC address to the host part of the IP address insert ff fe between the third and fourth octet and toggle the one but least significant bit of the first octet.

When a WAN connection is present, ther is at least one other IPv6 address, the SLAAC address. The prefix comes form the ISP, the suffix (least significant 64 bits, are derived from the MAc in the same way as for the LLA.

In windows with privacy extensions enabled (default) there are wone or more PE addresses. The host part is a64 bit random number that changes every 24 hours. Then there can be oneor more static addresses that are manually assigned and one more addresse assigned by DHCP6.

For a server you want to advertise an address that is as stable as possible. That means either a manually static address or a SLAAC address. They only change when the ISP changes the prefix. Which if you are lucky never or rarely happens.

here is what I have:


Ethernetadapter LAN-Verbindung:

        Verbindungsspezifisches DNS-Suffix: dynamic.ziggo.nl
        Beschreibung. . . . . . . . . . . : Broadcom NetXtreme Gigabit Ethernet
        Physikalische Adresse . . . . . . : 00-15-60-52-21-3D
        DHCP aktiviert. . . . . . . . . . : Ja
        Autokonfiguration aktiviert . . . : Ja
        IP-Adresse. . . . . . . . . . . . : 192.168.178.15
        Subnetzmaske. . . . . . . . . . . : 255.255.255.0
        IP-Adresse. . . . . . . . . . . . : 2001:1c02:1100:d800:b93b:f34d:c555:b46f
        IP-Adresse. . . . . . . . . . . . : 2001:1c02:1100:d800:215:60ff:fe52:213d
        IP-Adresse. . . . . . . . . . . . : fe80::215:60ff:fe52:213d%5
        Standardgateway . . . . . . . . . : 192.168.178.1
                                            fe80::cafb:26ff:fef2:296f%5
        DHCP-Server . . . . . . . . . . . : 192.168.178.1
        DNS-Server. . . . . . . . . . . . : 89.101.251.228
                                            89.101.251.229
                                            fec0:0:0:ffff::1%2
                                            fec0:0:0:ffff::2%2
                                            fec0:0:0:ffff::3%2
        Lease erhalten. . . . . . . . . . : maandag 11 juli 2016 0:39:44
        Lease l„uft ab. . . . . . . . . . : maandag 11 juli 2016 1:39:44


As you can see the fe80:: address is derived from tha MAC.  And s is the second IPv6 address. The first IPv6 address is a PE address. A new one is added every 24 hours. This snapshot was taken shorly after a reboot. The last PE address is the one used by windows for outgoing connections. Can't use that for incoming traffic because it changes every 24 hours.


Cheers, Michiel

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