Re: fe80::/128

[Tandankwa STANLEY Fon <[e-mail]>]

Mark,
Just to say that from what i have experinmented, IPv6 nodes are not fixed with particular default gateways. The nodes can use any of the routers as their gateway depending on which router's RA they are acting upon. If i received router X RA first, then i consider the information in his message. So, i would say think of the content of the RA, ND and that of the NS to an extend and this might help to resolve the issue.

Kind Regards
Tandankwa Stanley




On Thursday, March 27, 2014 9:33 AM, "Templin, Fred L" <[e-mail]> wrote:
 
Hi Mark,

> -----Original Message-----
> From: Mark ZZZ Smith [mailto:[e-mail]]
> Sent: Thursday, March 27, 2014 1:31 AM
> To: Templin, Fred L; [e-mail]
> Subject: Re: fe80::/128
> 
> Hi Fred,
> 
> 
> ----- Original Message -----
> > From: "Templin, Fred L" <[e-mail]>
> > To: "[e-mail]" <[e-mail]>
> > Cc:
> > Sent: Thursday, 27 March 2014 8:31 AM
> > Subject: fe80::/128
> >
> > I have a question. I have an IPv6 link on which the interfaces of all
> > nodes use link-local addresses only. The link has a few routers that
> > other nodes on the link see as IPv6 default routers. Each node will
> > associate with at most one default router.
> >
> > I would like to assign fe80::/128 as the "subnet router anycast"
> > address configured on the interface of each default router. My
> > question is, since each node will speak only to exactly one default
> > router, and since no default routers will speak to other default
> > routers, is it permissible for default routers to use fe80::/128
> > as the source address of neighbor discovery messages they send?
> >
> 
> I don't really know, I suppose it depends on whether any of the ND etc. related functions assume the
> link-local source address is unique and is an unicast address and can therefore be used to uniquely
> identify a router. I'd think that likely.
> 
> The comment I would make though is that if it is a requirement that in your scenario the use of
> fe80::/128 is only in use by one router, then I'd avoid using it. fe80::/128 is a reserved anycast
> address, and all routers are expected to configure it by default on their interfaces (as per RFC4291,
> 2.6.1). I think creating a special case exception requiring it to be a unicast address in a specific
> scenario would be error prone and easy to forget.

I'm not sure what common router implementations currently do with fe80::/128.
Do they really assign it to their router interfaces, or do they do nothing
with it at all? Is fe80::/128 really a reserved anycast address, or is it
a "nothing" and not specified at all by the specs? Do we need an update to
RFC4291 telling what to do with fe80::/128?

> So perhaps either make sure it would work if multiple routers on the link were using it as their link-
> local address, or pick another address to use (is the attraction its typing simplicity?)
> 
> (Somewhat related, I've thought it could be useful to statically configure on all links fe80::1,
> fe80::2 etc., as the routers' interface addresses, so that if you're asking an end-user to perform
> troubleshooting by pinging the default gateway address(es), it is easy for them to type.)

AERO is currently using fe80::1, but I was contemplating changing that to
fe80::0. But, some of the comments from yourself and other responders have
me wondering whether that would be a good idea.

Thanks - Fred
[e-mail]


> Regards,
> Mark.

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