Unanswered Question
Oct 26th, 2009

hello everyone

Can someone please clarify some questions for me on IPv6

1)I read about link local, site local, and global addresseses, which address relates to say my pc? will it have all 3 of them?

2)Is the link local address always start with the same thing, and does it include the cards mac address?

3)who assigns the site local address, and does the link local form part of this ?

4)who assigns the global addresses? and again, does the site or link local address form part of this?

I am confused as surely my pc wouldnt have 3 different addresses?

I have this problem too.
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Overall Rating: 4.5 (2 ratings)
simontibbitts Mon, 10/26/2009 - 03:56

Hi Carl.

1) Yes, this is the one of the advantages of IPv6, your PC will have all three addresses if they are needed. (link local is always needed) If you do a windows dos prompt 'ipv6 install' you are automatically given 4 virtual interfaces! Please note that 'Site Local' addressing has been replaced with 'Unique Local Addressing' as per RFC 3879.

2) Link local always starts with the first 10 bits as 1111111010. It doesn't always have to include the mac address of the interface, it just needs to be unique on that link. The EUI-64 way of assigning the link local address makes sure that it is uniquely generated.

3) The 'Unique Local Addressing' is assigned by yourself. But as per the RFC 4193 you need to make it unique. This link helps generate your own unique network address http://www.sixxs.net/tools/grh/ula/

4) Global addressing is originally provided by IANA, who assigns the addresses to the Reginal Internet Registries. For example RIPE (Europe) has been assigned 2001:06xx::/23 for which it assigns /32s to ISPs and then your ISP will assign you a /48. The host portion of this address will most likely be assigned by EUI-64 as well.

You need to get used to the idea that interfaces in IPv6 have multiple addresses.

Hope that helps


carl_townshend Mon, 10/26/2009 - 09:48

hi there many thanks for that

more questions :-)

how is the link local assigned then? can this be automatic?

and with the global address, would each and every pc in my office have a global IP also?

and which address would be where my vlan's reside ?

also, how about default routes ?



simontibbitts Mon, 10/26/2009 - 11:49

Hi Carl.

>> how is the link local assigned then? can this be automatic?

Yes, it is mainly automatic. As soon as you configure an IPv6 address on an interface then it automatically creates a link local address. You can also use the interface command 'ipv6 enable' which assigns an link local address to the interface. If you want to create one manually the interface command is 'ipv6 address FE80::1 link-local'

>> and with the global address, would each and every pc in my office have a global IP also?

Everything that needs to get to another global address will. Things like printers don't need a global address as normally they don't need to access the internet.

>> and which address would be where my vlan's reside?

When you are given your global /48 then it is up to you to allocate your networks to your different vlans as you see fit.

>> also, how about default routes ?

Default routes are just the same just in IPv6 format 'ipv6 route ::0/0 Serial2/3' If you specify a next hop address the RFC recommends to use the link local as the next hop otherwise IPv6 redirection will not work.

Recommended reading:



carl_townshend Mon, 10/26/2009 - 13:44

hi there

thanks for your response, how about the unique site address? what address will we have to put on say my pc, and router interfaces ? would we put the global address in and the unique local?

im a little confused about this, could you do a simple walkthrough?

also would the remider of the address always be in HEX?

and lastly, which portions of the address is subnet, and host etc ?

carl_townshend Tue, 11/03/2009 - 08:31

hi all

with Link local addressing, would vlans seperate this, ie can link local addresses only see other link locals in the same vlan ?

Giuseppe Larosa Tue, 11/03/2009 - 09:21

Hello Carl,

yes link local addresses are confined to a single Vlan / broadcast domain.

this is the reason why they are not routable: it is always the same prefix in all possible segments.

However, as Simon has explained in his good posts link local is important in IPv6.


I think Simon's posts should be rated as I did for his first one

Hope to help


carl_townshend Wed, 11/04/2009 - 06:04

hi there

thanks for your reply,

can you also tell me if the unique local addresses are also split into vlans? and is this the same with the global ip's too ?

Giuseppe Larosa Wed, 11/04/2009 - 06:19

Hello Carl,

unique local are routable so you can allocate a different /64 within unique local range for each Vlan/broadcast domain

the same happens for global ip addresses

As noted by Simon an IPv6 interface has multiple unicast IPv6 addresses associated to it.

This concept is new in ipv4 you can have secondary ip addresses on routers but NICs have only one address

Hope to help



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