IPv6 universal/local bit
Muslimtech posted the following question on the IPv6 Link-local article:
“hi man
i want ask you Q About U\L Bit
i read that in Bsci
Universal/Local (U/L)
The seventh bit in an IPv6 interface identifier is referred to as the universal/local bit, or U/L bit. This bit identifies whether this interface identifier is universally or locally administered.
If the U/L bit is set to 0, the address is locally administered. The network administrator has overridden the manufactured address and specified a different address.
If the U/L bit is set to 1, the IEEE, through the designation of an ISP, has administered the address
i cant understand How U\L Bit = 0 i want Ex; About that
and whene he say “locally administered” mean
i use command to change mac address for interface ??
or what”
IPv6 Summarization
Summarizing IPv6 addresses is quite similar to the summarization of IPv4 addresses. The only real differences are:
- IPv6 is 128bit while IPv4 only has 32 bits
- IPv6 is written in HEX while IPv4 is written in decimal
If we take those two differences into account the summarization is the same.
IPv6 Link-Local Address
Link-local addresses only have a scope of the link they are used on, they will not be used or even reachable from another link.
The link-local address of an interface is a mix between the BIA (Burned In Address) and some static IPv6 stuff. The “dynamic” part is also know as modified EUI-64 addressing.
First of all, every link-local address in IPv6 is generated from FE80::/10, so if you ever see a address starting with FE80 you know thats a link-local address 
Over a sh int you see your BIA:
R1#sh int fa 0/0
FastEthernet0/0 is up, line protocol is up
Hardware is AmdFE, address is cc00.0bfc.0000 (bia cc00.0bfc.0000)
About
Im a network engineer working for an international medical company based in Basel, Switzerland. I began my professional life in 2000 after 4 years of an IT apprenticeship. I started as the Network Management System responsible with quite a lot other of other tasks inside the Cisco networking field. In 2005 I changed to my current employer where I changed my field of knowledge from part NMS part Networking to full time Networking. I also started to educate myself deeper into networking. After passing the CCNA and CCNP exams I wanted to go further with my education and took the CCIE R&S track instead of doing a school with lots of stuff Im not interested in 
I started the CCIE journey in August 2007 with the first of 5 workshops at the Cisco Network Academy in Rapperswil and passed the CCIE in Brussels at 07th of May 2008.
During that time I wrote a lot of documents to keep the stuff I learned and I thought it might be an idea to make it public so it might help other people on their path through the Cisco Certifications. I hope this site gets useful not only for CCIE candidates but also for other networking professionals on their search for knowledge.
If you have any questions or want to contact me, please drop me a line to pashtuk at gmail.com
