[Nfd-dev] Using Forwarding Hints

[Philipp Moll]

On 10/17/19 4:26 PM, Lixia Zhang wrote:

Thank you for your response, it helped a lot. Please note my follow-up 
questions/comments inline.

>
>> On Oct 17, 2019, at 6:02 AM, Philipp Moll <philipp.moll at itec.aau.at> wrote:
>>
>> Hi all,
>>
>> I wonder if there there is any documentation about using ForwardingHints available? I think I got an idea how everything works by checking out the NFD implementation, but some details are still unclear. Is there additional documentation besides the code?
> not sure but I might be the guilty party for the missing of this doc (I vaguely recall I agreed to write something about forwarding hints a few years back, after I had some discussion with Haitao to clarify a couple confusing points, but unfortunately that item is still pretty far down my TODO list)
>
> Unless such a doc existed somewhere else already, otherwise I could take this msg of yours as a starting point, and you could help as well :-)
Sure, I think that I will need forwarding hints in my upcoming work, I 
gladly help documenting them after using them for a first time and 
thereby better understanding their behavior and the implications of 
using forwarding hints.
>
>> In the NFD code, I saw that the forwarding hint is used by forwarding strategies and stripped by the forwarder when the Interest has reached the ProducerRegion.
> correct (according to my understanding)

OK, until looking at the code I thought that the implementation of the 
forwarding hint follows the SNAMP paper [1]. However, the paper states 
that "When this modified interest reaches the first router that cannot 
find a matching FIB entry for the interest name, the router will extract 
the prefix delegations from the attached link object (see Section II-E), 
select the best candidate (e.g., by using routing cost or based on 
previous traffic measurements), and forward the interest based on this 
selection.".

This would mean that the forwarding hint is only used if no FIB entry 
for the Interest name is found. In the actual implementation, it looks 
to me (maybe I am wrong) that the forwarding hint is used as soon as a 
forwarding hint exists, which is different from the behavior described 
in the paper. No need to justify, I just wonder if there is a reason why 
the implementation differs from the behavior of the paper.


[1] Afanasyev, A., Yi, C., Wang, L., Zhang, B., & Zhang, L. (2015). 
SNAMP: Secure Namespace Mapping to Scale NDN Forwarding. 18th IEEE 
Global Internet Symposium. Retrieved from 
https://named-data.net/wp-content/uploads/2015/03/SNAMP-NDN-Scalability.pdf

>
>> I also found that the NetworkRegionTable stores the ProducerRegions of the node. It seems that ProducerRegions can be configured statically in the ndf.conf file. Is the nfd.conf file the only possibility to configure ProducerRegions, or is it possible to change it via nfdc as well?
> for this, I do not know the answer; need people from NFD management.
>
>> Also, when using NLSR, are the ProducerRegions advertised, or not?
> No. Again according to my own understanding, the "ProducerRegion" is simply a property of the local node.
>
>> If there is any additional documentation, or examples available, I would appreciate to get some pointers. So far, I only found the hint that "Specifics of the forwarding logic for Interests with ForwardingHint will be defined in a separated document." on http://named-data.net/doc/NDN-packet-spec/current/interest.html , but no separated document.
> I think additional info that might be useful in this doc is how one may get a forwarding hint; there can be a few options, and this doc should show examples.
>
> my 2 cents,
> Lixia