Take the 2-minute tour ×
Server Fault is a question and answer site for professional system and network administrators. It's 100% free, no registration required.

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?

share|improve this question

migrated from stackoverflow.com Mar 2 '11 at 2:29

This question came from our site for professional and enthusiast programmers.

1 Answer 1

up vote 1 down vote accepted

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 192.168.0.1 or 10.1.1.1 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)

share|improve this answer
    
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 '11 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 '11 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. –  Mark Henderson Mar 2 '11 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 '11 at 20:20

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.