Re: IPv6 Anycast

Nathan,

I think it turns of IPv6 DAD detection for that address. Run "debug ipv6 nd"
when you enable a unicast address and an anycast address. When you have an
anycast address, the router sends an NS instead of sendng an NA and waiting
to see if it unique.

R2(config-if)# ipv6 address 2002::2/64

*Mar 1 03:36:55.771: ICMPv6-ND: Adding prefix 2002::2/64 to Serial1/1
*Mar 1 03:36:55.775: ICMPv6-ND: Sending NS for 2002::2 on Serial1/1
*Mar 1 03:36:56.779: ICMPv6-ND: DAD: 2002::2 is unique.
*Mar 1 03:36:56.779: ICMPv6-ND: Sending NA for 2002::2 on Serial1/1
*Mar 1 03:36:56.783: ICMPv6-ND: Address 2002::2/64 is up on Serial1/1

R2(config-if)# ipv6 address 2003::2/64 any

*Mar 1 03:37:06.471: ICMPv6-ND: Adding prefix 2003::2/64 to Serial1/1
*Mar 1 03:37:06.471: ICMPv6-ND: Sending NA for 2003::2 on Serial1/1
*Mar 1 03:37:06.475: ICMPv6-ND: Address 2003::2/64 is up on Serial1/1

On Fri, Oct 9, 2009 at 9:34 AM, Nathan Richie <nathanr_at_boice.net> wrote:

> So I understand the concept behind the Anycast feature of IPv6. But what I
> am
> failing to understand is the "anycast" option when configuring the ipv6
> address.
>
> I assume it is so that the router is aware that the assigned address is an
> Anycast address, but I fail to understand why the router needs to know
> that.
> I have read the documentation from Cisco Doc CD and all it says is:
>
> "Assigning a unicast address to more than one interface makes a unicast
> address an anycast address. Nodes to which the anycast address is assigned
> must be explicitly configured to recognize that the address is an anycast
> address."
>
> Can anybody help me understand why the address must be recognized as an
> Anycast?
>
> Thanks,
>
> Nathan Richie
>
>
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-- 
Bryan Bartik
CCIE #23707 (R&S), CCNP
Sr. Support Engineer - IPexpert, Inc.
URL: http://www.IPexpert.com
Blogs and organic groups at http://www.ccie.net