[Babel-users] Propagation of unknown sub-TLV?

[Lorenzo Ghiro]

Thank you, a reply so full of insights!

Please let us know what you decide -- I'll be glad to give a hand if
> you're not sure what to do.


mm, up to now we imposed every node to originate at least a route, so that
it was easy to disseminate router-ids in the whole network and run the
centrality algorithm.

But to be more general and if we really want to keep thinking at a
node-layer, then it seems
to be no escape: we will have to implement a per-node flooding mechanism...

I am wondering if we can be more elegant and integrate our algo with Babel
relying
only on interface-identifiers or prefixes, somehow avoiding flooding, or
even if it is worth
to stop thinking at a node-layer and consider the network at a
"prefix-layer"...

So well, we definitely do not have any decision for the moment, we need
some time to
think about it in much more details :)

Thank so much for now,

Lorenzo


2018-01-25 16:23 GMT+01:00 Juliusz Chroboczek <jch at irif.fr>:

> Ok, I see.
>
> > The algorithm let every node in a network compute its own value of "Load
> > Centrality" and afterwards let nodes disseminate computed indexes so
> > that each node, at convergence, is aware of the centrality index of all
> > nodes in the network.
>
> [...]
>
> > For the moment forget that actually Updates advertise distances
> > associated to prefixes, not to router-ids...we just wanted to work on
> > a network graph-layer.
>
> That's the whole point.  Babel is a distance vector protocol, it
> advertises routes to given prefixes.  Now, of corse, prefixes are
> originated by nodes (that's what the router-id identifies), but Babel does
> not flood information about nodes:
>
>   - if a node originates no route, then it doesn't appear on the wire at
>     all (Hello and IHUs carry interface identifiers, not node identifiers);
>   - if a given prefix is advertised by multiple routers, then parts of the
>     network will only see one of the routes to that prefix;
>   - finally, Babel doesn't use a reliable transport -- under heavy packet
>     loss, part of the information may be dropped (which is okay for its
>     intended purpose -- if there's such heavy packet loss, then there's no
>     point advertising routing information, since the routes are unusable
>     anyway).
>
> In other words, Babel, as it currently stands, does not have provisions
> for advertising node-specific information globally.
>
> > Do you think the "transitive attributes" feature could be of general
> interest?
>
> As a general rule, we try to avoid adding to Babel features that are not
> useful for routing.  You could do one of the following:
>
>   - design your own reliable flooding protocol; that's not difficult, I've
>     given it as a project to fourth year students and almost everyone
>     succeeded;
>   - piggyback on a protocol that does reliable flooding, such as IS-IS or
>     OSPF;
>   - piggyback on a protocol that does unreliable flooding, such as OLSR or
>     HNCP;
>   - add a subprotocol for flooding of per-node information to Babel, but
>     to be entirely frank with you, I doubt it will get into mainline
>     babeld.
>
> Please let us know what you decide -- I'll be glad to give a hand if
> you're not sure what to do.
>
> -- Juliusz
>
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