Re: [Coin] SDN, Network Programming, and Semantic Routing

Jon,

Indeed, most of the SDN draft content is concerned with the forwarding, not routing aspect, indeed. 

I also agree that the network-wide algorithmic aspect is what I see least in the context of COIN, while the SDN action-focused aspect is (there are pointers to progressing towards P4 in the document, something we considered in the work referenced in the document that I led in a past EU project). 

As for a survey, I'm equally interested in that as you are. 

Best,

Dirk

-----Original Message-----
From: Jon Crowcroft [mailto:Jon.Crowcroft@cl.cam.ac.uk] 
Sent: 04 February 2022 09:38
To: adrian@olddog.co.uk
Cc: coin@irtf.org; Dirk Trossen <dirk.trossen@huawei.com>om>; mohamed.boucadair@orange.com; 'George Xylomenos' <xgeorge@aueb.gr>gr>; Jon Crowcroft <Jon.Crowcroft@cl.cam.ac.uk>
Subject: Re: [Coin] SDN, Network Programming, and Semantic Routing

for me that the phrase semantic routing includes the word "routing" implies one (and not forwarding) has to consider network wide algorithms  - the sort of thing predicate routing and meta-routing do (see prev message and this https://www.cl.cam.ac.uk/research/srg/netos/papers/2002-predicate-routing.pdf
and all the work on replicared/coordinated SDN controllers and consensur/converegence/replication etc

most the questions below are "just" the forwarding treatments

how these are installed on a node is just a simple protocol/api though how the node is programmed to carry out those treatments efficiently (s/w and h/w requirements, as you've discussed) are obviously a moving target and of interest here for sure... next gen of SDN & whatever is after P4 are obviously things to work on 

how they are created, verified, made sense of in a network-wide sense (whatever scope that network has) is where I think the harder research challenges lie...
but perhaps are the least coin-like aspect - it would be cool to survey what sorts of policy engines are out there besides the very cool cloudflare stuff as input to that (if anyone knows of such a survey, pointers most welcome!!)

> Hi yet again,
> 
> With this email we get on to some of the serious topics for fitting 
> Semantic
> Routing into the context of COIN.
> 
> As we know, a significant part of what COIN is looking at is programmable
> networking and programmable network devices. In this context, the concept 
> of
> programmability is pretty broad ranging from what we have known for years
> (installation of forwarding entries through management system commands -
> CLI, TL1, SNMP, Netconf/YANG), through the more recent development of new
> languages for installing network actions (OpenFlow, P4, BGP policies).
> 
> There are several critical questions to be asked:
> 
> - Is the programming installing forwarding actions based only on
>   "traditional" lookups (typically the 5-tuple, and other flow
>    classification fields), or is it telling the network node to look at
>    other places in the packet?
> 
> - Is the programming coordinated with packet classifiers and
>   markers so that additional information is placed in the packets
>   and used by the network nodes?
> 
> - Is the use of programming the only solution, or is SDN just *an*
>    approach that sits beside or can be integrated with other
>    techniques including "traditional" routing systems?
> 
> - What are the risks to the forwarding system arising from an
>   SDN controller-based system in terms of scalability, flexibility,
>   responsiveness, stability, and vulnerability to failures and attacks?
> 
> - What is the potential for using programming to install algorithms
>   on network devices such that they perform selective forwarding
>   actions dependent on semantic routing information? What are
>   the risks of inconsistent processing on different nodes, and
>   how does the OAM work in such situations?
> 
> This last point will be the subject of a separate thread as it moves 
> beyond
> "network programming" and into "compute in the network".
> 
> It is worth repeating that in all of this discussion, the scope of 
> semantic
> routing remains at the IP-forwarding level. That is, programming functions
> and features above and beyond those used for next-hop routing at the 
> packet
> forwarding layer is out of scope. That is not to say it is not interesting
> and valuable in many scenarios, just that it is not what is handled by the
> forwarding engines.
> 
> In order to start to capture where our thinking is at, and so provide a
> basis for more in-depth discussions, we have posted
> https://datatracker.ietf.org/doc/draft-boucadair-irtf-sdn-and-semantic-routi
> ng/ This is very much "work in progress" as we are still collecting our
> ideas and have a way to go. The references are heavily oriented towards
> existing engineering solutions, and we have some work to do to also 
> include
> the academic and research references. We would appreciate being told where
> we are wrong by experts in SDN and network programming. We would also
> appreciate ideas about how SDN controllers can keep an entire network "in
> synch" so that they are sure that there is consistent forwarding and loops
> and data sinks are avoided.
> 
> Cheers,
> Adrian
> 
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