Re: [6lowpan] "Advertize on Behalf" flag in ARO

Hello,

as far as I understand RPL reachability is indeed advertised to both 6LR/6LNs, the only distinction is that a 6LN (host) would operate as a RPL leaf node (as in section 8.5 of rpl-19). So a 6LR does not have to 'detect' first whether another node is 6LR or 6LN.

best regards,
Esko Dijk

-----Original Message-----
From: 6lowpan-bounces@ietf.org [mailto:6lowpan-bounces@ietf.org] On Behalf Of Erik Nordmark
Sent: Tuesday 29 March 2011 13:14
To: Mukul Goyal
Cc: 6lowpan
Subject: Re: [6lowpan] "Advertize on Behalf" flag in ARO

On 3/3/11 5:07 AM, Mukul Goyal wrote:
> Hi all
>
> Recently Anders pointed out the need for the "Advertize on Behalf"
> flag in an Address Registration Option (ARO).
>
> We would not have needed this flag if only a host could send a
> unicast NS containing an ARO. However, the way I read Section 6.5.5
> in nd-15, a 6lowpan router (6LR) can also send a unicast NS to
> another 6lowpan router. This means that a registered neighbor cache
> entry (NCE) in a 6LR could refer to either a host or another 6LR. So,
> how does a 6LR know that a registered NCE belongs to an attached host
> and it should advertize reachability to this host in the routing
> protocol, such as RPL, it is running?
>
> The proposed flag will solve this problem. A host would set
> "Advertize on behalf" flag when it sends an ARO inside a unicast NS
> message, whereas a 6LR wont.
>
> I was wondering if ND authors could comment on this.

I didn't see anybody else comment, so let me try.

I don't know what assumptions RPL makes in particular, but if we are
talking about a general case of a routing protocol, I don't see why
there would be a need to tell a difference between a host sending an ARO
and a router (which might be initializing and haven't yet enabled
routing and forwarding) sending an ARO.

In both cases I'd assume that the unicast address that is registered is
something that should be reachable, hence it makes sense advertising
reachability to that address.

If this isn't the case, then a routing protocol would typically find out
about its neighboring routers IP addresses, and from that it can decide
to treat those IP addresses differently than the addresses assigned to
hosts.

    Erik
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