IPv6 @ Loughborough University

IPv6 is the next generation of the IP protocol. The current version which is in widespread use - and is present in most Internet traffic is IPv4. IPv6 adds new technology and abilities into the mix - and vastly increases the address space available to hosts on the Internet.

Unfortunately, the new abilities and addressing require a new 'Internet stack' and requires new and extra network configurations to be undertaken. Latest Linux distributions, MacOSX, Windows XP and Solaris 8 onwards all support IPv6, as do the CISCO core and edge switches deployed on the university campus.

The main change that users will see, however, is their address. Instead of a dot-quad address (4 8bit numbers separated with dots e.g. the IPv6 address is a 128 bit address created out of 8 16bit numerators, separated with colons. e.g.


Now, don't be scared of this address. The following paragraphs describe how your IPv6 address at Loughborough University is derived.

Your IPv6 address is a lovely number which is best looked at as 3 sections of the full 128bit code. The first 48 bits represent the Public Routing Topology (PRT) - this is the address location that JANET assign Loughborough University. This is 2001:0630:0301. In IPv4 terms (CIDR-wise) this would be 158.125, or 131.231. We now have far more address space under IPv6 so we just need a single ID block. Leading 0's can be removed. so really this is 2001:630:301 (incidentally, 2001:630 means that it is a JANET address!)

Now, under this address we have a /16 network space, each bit of which has its own /64...ie


through to


The 16bit space - :: through to :FFFF: is where we get all of our network address space from. Don't worry if you're a bit lost at this point. It all becomes clearer when the space is broken up in the description to follow.

The last 64bits (represented by the /64) is the L2 address (MAC hardware address) of your computer after its been put through an algorithm to convert it to 64bits in length. This part is known as its 'EUI-64 address' and works as follows...

"first 3 bytes of MAC" "2 bytes of a constant" "last 3 bytes of MAC"

00:90:27:57:A3:D9 turns into 0090:27FF:FE57:A3D9

(if the constant, in this case, was FFFE. This constant bit can be unset, or derived from a pseudo-random equation for encryption.

The 16bits that exist between the 48bit PRT and the 64bit EUI are called the Site-Level Aggregation ID (SLA-ID). The SLA-ID is constructed into the following form.

The first 4 bits define the campus location (east site, west site, central etc) the next 12 bits define the logical network VLAN on which the address sits. This gives the Loughborough University network, on IPv6, 12 unique locations each with their own 4096 VLANs. Each of these VLANs could host 65,536 machines! Thats a huge number of machines/systems/access points and should serve the University well!

An example address

After all the theory and low-level description, here is an example:

2001 630 301 11FE 90 27FF FE57 A3D9

Valid HTML 4.01!

Alan Buxey 15/Nov/2004