Re: ipv6 - link local uses

Thanks gary, why would the link local that you statically mapped no longer be
the same?

I saw that ping thing too asking me outgoing interface , guessing this has
something to do with what you and Brandon said..... Fe80::/64 exists on every
interface, so router doesn't know which of its possible several interfaces to
send that traffic out ... True? Isn't this one of those radical differences
from ipv4 ?! Since when were you ever able to duplicately assign a same or
overlapping subnet on multiple interfaces of same router ( nevermind vrf ) ?

Thanks for emphasizing that LL is actually the range covered by
/10....fe8-feb

Are you saying that if I leave LL to default fe80::/64 that a router with
multiple connections won't know how to forward traffic for certain situations
like frame relay?

Aaron

On Mar 24, 2011, at 1:07 AM, garry baker <baker.garry_at_gmail.com> wrote:

> 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 - 09:41:46 ART