QID:NH84 stateless auto-configuration of global unicast from Link-local address

[joshuad31]

Hello,

Please see:  http://www.cisco.com/web/about/ac123/ac1...onfig.html

This link clearly explains that a requirement of a link local address is that the following 16 bits are inserted in the middle of the 48 bit mac address making for a total of 64 bits:  ff:fe

Your link local address is FE80::A1:56C2:1102
but if the MAC address is 00A1:56C2:1102 then your address should be FE80::A1:56ff:feC2:1102

When changing a link local prefix to a global prefix the following would then be performed, the host would see that the router is sending a prefix of /64 and thus would take and append the last 64 bits of the link local address and would append then first 64 bits of the given prefix of its router.  Thus the correct answer is:

2001:AAAA:BBBB:CCCC:A1:56ff:feC2:1102/64

2001:AAAA:BBBB:CCCC:FE80::A1:56C2:1102 - this cannot be an answer because the double colon is an incorrect rendering of a proper IPv6 address.  There are already eight 16 bit sections... so why is there a :: double colon when it would represent a minimum of one 16 bit section of all 0000 s?  That address implies that there is such a thing as an IPv6 address with 9 sections of 16 bits, which is incorrect.

35. (QID:NH84) A workstation has a Link-local IPv6 address FE80::A1:56C2:1102 and is setting a global unicast IPv6 address via stateless auto-configuration. The router connected to the LAN has a global IPv6 address of 2001:AAAA:BBBB:CCCCDDD::l/64. What will your workstation set its IPv6 address to once it detects the router advertisements?

2001:AAAA:BBBB::A1:56C2:1102
2001:AAAA:BBBB:CCCC:FE80::A1:56C2:1102
2001:AAAA:BBBB:FE80::A1:56C2:1102
2001:AAAA:BBBB:CCCCDDD:A1:56C2:1102

Correct Answer: 2001:AAAA:BBBB:CCCC:FE80::A1:56C2:1102

Please correct

Joshua

[forumsupport]

Yes, given answer is incorrect, but your answer is also incorrect.
Given Link-local IPv6 address is FE80::A1:56C2:1102. No need to insert FF:EE. This step is needed when only MAC address is given.

Appending it with 64 bit prefix received from the router we get:

2001:AAAA:BBBB:CCCC::A1:56C2:1102
OR
2001:AAAA:BBBB:CCCC:0000:00A1:56C2:1102

right?

[joshuad31]

Well... That is a better answer for sure than the one previously stated.  I guess I am just confused why there is a missing 16 bits of ff:fe but I am not an expert on this subject.  If I happen to find out more information I will relay it to you but the new answer you suggested seems to be the best possible answer.