Re: ipv6 - link local uses

it is automatic, but doesnt have to be can be staticlly defined which can
save you a world of headache when reading the output of the 'show ipv6 int
br' and debugs, also in the lab when you are doing frame-relay and routing
and change routers and the link-local that you staticlly mapped is no longer
the same...

FE80::/10 for link-local addressing

FE80:: - FEB::

when i first started with IPv6 i couldnt see this concept until i setup R1
<-> R2 with two serial connections and then i set interface s0/0 and s0/1
with the same link local address on R1 FE80::1 <-> R2 FE80::2 on both s0/0
and s0/1 and then did a ping and it asked me for the output interface...

also play with this link-local range to see the full address space, the
router will complain when you get out of range using the 'ipv6 address
link-local' command

R1 FE80:1 <-> R2 FEBF::2

and then run some 'debug ipv6 packet' and let the fun begin

http://tools.ietf.org/html/rfc4291#section-2.5.6

Link-Local addresses are for use on a single link. Link-Local
   addresses have the following format:

   | 10 |
   | bits | 54 bits | 64 bits |
   +----------+-------------------------+----------------------------+
   |1111111010| 0 | interface ID |
   +----------+-------------------------+----------------------------+

   Link-Local addresses are designed to be used for addressing on a
   single link for purposes such as automatic address configuration,
   neighbor discovery, or when no routers are present.

   Routers must not forward any packets with Link-Local source or
   destination addresses to other links.

 --
Garry L. Baker

"There is no 'patch' for stupidity." - www.sqlsecurity.com
"Complexity is the enemy of reliability..."

On Wed, Mar 23, 2011 at 10:44 PM, Aaron <aaron1_at_gvtc.com> wrote:

> I understand ipv6 has some very interesting and very different things from
> ipv4.
>
>
>
> One of which is this link-local business (fe80::/64 as I recall), seems to
> be an automatic ipv6 address on pretty much every single ipv6 product that
> I've laid eyes on.cisco, linux, windows.
>
>
>
> Question, is it possible, furthermore, is it a best practice to run purely
> link local subnets between routers? OR must I configure real-world ipv6
> address (I think called aggregatable global ucast) between my routers ? ..
> I would understand the need for agg global's on customer facing interfaces
> but on the router to router links...that's where I'm wondering.
>
>
>
> Aaron
>
>
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Received on Thu Mar 24 2011 - 09:07:38 ART