[Babel-users] Multiple internet gateways in the mesh

[Juliusz Chroboczek]

Your comments reordered.

> Very much appreciate the help! This personal project was designed to teach
> me a little about routing and it has definitely served that purpose
> well :)  But perhaps learning a little about routing isn't the same as
> being very good at routing!

Distributed algorithms are tricky.  They impose constraints that seem
arbitrary if you don't have a full understanding of the algorithm.  The
interesting bit is how to commnicate these constraints to the users in
a way that they understand, but unfortunately doing that does not lead to
publications :-/

> I used to use a central database to coordinate where the "main route out"
> was installed, but that was a little vulnerable to issues "in the
> center".

You've essentially reinvented SDN.  You're replacing a distributed
algorithm (tricky) by a central controller (much easier), which is an
effective way of lifting the seemingly arbitrary constraints at the cost
of introducing a central point of failure.  It works very well in the
datacenter, not so well in geographically distributed networks.

> Unfortunately, because I don't control the ISP routers, I don't think
> I have a border router by this definition.

Right.

> As a final thought, I think what I want is effectively
> "install-duplicate-if-lowest-metric". In other words, imagine I had
> a local default route out with a metric of 128 and a proto of 250, and
> babel config like this:

Yes, it looks like a new mechanism is needed.  I need to think it over,
it's not immediately obvious how your proposed mechanism interacts with
Babel's loop-avoidance mechanisms.  (At first sight, it might cause
persistent oscillations, at least in some topologies.)

-- Juliusz