IOS-XR DAD: Duplicate IPv6 address

[kozorezdi]

Hello everyone,

IPv6 on my PtP links were blocked.  After "clear ipv6 duplicate addresses" it's Up and Running.

TenGigE0/0/0/0 is Up, ipv6 protocol is Down, Vrfid is default (0x60000000)

  IPv6 is down (link local duplicate), link-local address is fe80::c262:6bff:feb0:e136 [DUPLICATE]

RP/0/RSP0/CPU0:frankfurt02#sh ipv6 interface | in DUP        

...

IPv6 is down (link local duplicate), link-local address is fe80::c262:6bff:feb0:e136 [DUPLICATE]

...

During such situatino, how can I find where is the same link-local address?

Why I had such issue? 

Thank you in advance.

--

Dmitry

[Rolf Fischer]

Dmitry,

this are auto-configured EUI-64 ("Extended Unique ID") addresses.

Normally they should be unique because they are derived from the MAC-address:

FE80::

C2-62-B6 (MAC OUI, not present in the IEEE Public Listing !?)

FFFE (indicates an EUI-64 address)

B0-E1-36 (MAC Organizationally Unique Address part)

To avoid that (and to make troubleshooting easier as well), you could assign simple link-local addresses like FE80::1, FE80::2, etc. manually - especially on point-to-point links:

(config-if)# ipv6 address FE80:: link-local

HTH

Rolf

[kozorezdi]

Hi Rolf,
about C2-62-B6 (MAC OUI, not present in the IEEE Public Listing...
RP/0/RSP0/CPU0:frankfurt02#sh int TenGigE0/0/0/0 | in Hardware
Hardware is TenGigE, address is c062.6bb0.e136 (bia c062.6bb0.e136)

It is Cisco, no doubts 
  C0-62-6B   (hex)          CISCO SYSTEMS, INC.
  C0626B     (base 16)          CISCO SYSTEMS, INC.
From:
http://technet.microsoft.com/en-us/library/bb726944.aspx

Mapping IEEE 802 addresses to EUI-64 addresses:
ccccccug cccccccc cccccccc xxxxxxxx xxxxxxxx xxxxxxxx  
For link-local address we need to mark it as Localy significant... 
Complement the U/L bit (seventh bit of first byte):
The first byte in binary form is 00000000.
When the seventh bit is complemented, it becomes 00000010 (0x02).  

u bit – Universally (=0)/Locally (=1) Administered

It is clear that we can use fixed link-local address, but to me not clear why we have this situation when they duplicated somehow...  Anyway thank you for your message.

--

Best wishes,

Dmitry

[Rolf Fischer]

Hi Dmitry,

OMG - how could I overlook that... Embarrassing

Thanks and sorry for the useless answer!

Regards

Rolf

[kozorezdi]

hi Rolf,

no problem.  at least, we both will be keeping this small moment about U-bit in our heads

Have a nice day,

Dmitry