Re: [Roll] Clarification on SenderRank in RPL HbH option

[Dario Tedeschi <[e-mail]>]

Can anyone clarify this for me or at least indicate if it has already 
been discussed some time in the past.

- Dario

On 09/10/2012 11:50 AM, Dario Tedeschi wrote:
>
> While writing ZigBee-IP test procedures for RPL and discussing with 
> other ZigBee-IP members, it appears there may be an error in RFC 6550.
>
> RFC 6550 says:
>
>   SenderRank: 16-bit field set to zero by the source and to
>          DAGRank(rank) by a router that forwards inside the RPL network.
>
> Firstly, it seems wrong that the source of a datagram would set its 
> SenderRank to zero. If this packet were moving up the DAG the first 
> forwarder would set the Rank-Error bit to 1, because the SenderRank 
> field in the HbH option would be lower than its own rank. Similarly, 
> if the datagram were mistakenly moving down the DAG, where the 
> source's real rank was higher than the forwarder's rank a potential 
> routing loop could be missed.
>
> Secondly, why is DAGRank(rank) used to set SenderRank, when SenderRank 
> is a 16bit field. Wouldn't doing this allow for potential routing 
> loops to be missed?
>
> Could someone (preferably one of the RPL authors) please clarify.
>
> - Dario
>