What is the difference between link-local address and global link address in ISATAP?

For example:

link-local address: fe80::5efe:c000:0201
global address: 3ffe:b00:1:2::5efe:c000:0201

Why don't we use just one address? Why it is helpful to use both?

1 Answer 1


Any IPv6 adapter should always have two IP addresses if you're using it for internet traffic - your link-local address and your global address.

Your global address is world-routable, so anyone anywhere in the world can see that IP address (although of course, there should be a firewall between you and them to stop them from actually accessing you).

Your link-local address is just for your local area network. Consider it the equivalent of a or address. They are not routable, and can be used for internal communications, so that if your world-routable prefix changes, you don't have to update all your IP references to internal IP addresses.

The only functional difference is that your link-local address is not routable, and your global address must be routable. There are issues where non-routable global addresses have been allocated (via DHCPv6) for whatever reason, your computer THINKS it has a routable IPv6 address when it doesn't, and then all your IPv6 connectivity breaks.

I also notice that your global IP address has been assigned manually with a dot-decimal address, which makes me wonder if your IPv6 network is configured correctly as it's obviously not using auto-config with RA announcements)

  • Hi, thanks for your concrete answer. This holds true for ISATAP. How about 6to4 tunneling? i see that there is only one address of IPv6 which is created based on ipv4 address? So I guess it is Ipv6 link-local address but then it is absent of ipv6 global address. Please correct me if I am wrong. Thanks in advance.
    – JoesyXHN
    Mar 2, 2011 at 0:16
  • One more thing: fe80::a124:45f6:b8d7:cf7f%41 => this is a link local address I suppose? what does % mean? thanks
    – JoesyXHN
    Mar 2, 2011 at 0:30
  • @Joe - the % sign indicates which adapter the IP address is in. As far as 6to4, I've never really done much of it so I won't be much help Im afraid. Mar 2, 2011 at 1:07
  • On the 6to4, the address generated is a /48, so you can subnet that into 65k different subnets, each with a full /64 of host addresses.
    – Chris S
    Mar 2, 2011 at 20:20
  • 1
    Your comparison is misleading because RFC 1918 addresses are not link-local. The link-local addresses in IPv4 are as defined in RFC 3927.
    – kasperd
    Jul 10, 2015 at 7:15

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