[Babel-users] Roaming at layer 3

[Juliusz Chroboczek]

We had a not-long-enough chat with Mitar and Jernej yesterday about
roaming.  Here's a quick summary and some ideas.

Wlan-SI are deploying a massive infrastructure across all of Slovenia and
parts of neighbouring countries.  They achieve multihoming by tunnelling
to a central server, so no source-specific routing is required.  They're
currently using OLSRv1, but are in the process of transitioning to Babel.
Hosts are not participating in the routing protocol, they use traditional
DHCPv4/RA on their access points.

Since they need to scale to thousands of routers (and probably tens of
thousands of hosts), using a single L2 domain won't work for them.
However, they would still like to have roaming support -- the typical use
case being a large house with multiple access points.  If I understood
correctly, they're not trying to support wide-scale roaming -- the roaming
domains will be small and well-defined.

After some discussion, we agreed that Mikrotik's solution to this problem,
while inefficient, is quite reasonable: they're bridging the interfaces in
a home using "EoIP", which is just Ethernet over GRE over IP.  Since the
encapsulation will be local to the home, the resulting fragmentation
should not be a serious problem.  Mitar indicates that they have
high-speed links, which precludes userspace forwarding.

A quick web search indicates that Ethernet over GRE is supported by the
Linux kernel as "gretap".  I have no idea whether this is the same as RFC
3378, and I don't know whether it would be preferable to use the softwires
standards.

For the longer term, we should be looking at pure layer 3 roaming
solutions, at least for IPv6, since that would allow roaming at a global
scale.  The simple solution would be to run Babel on the host (which
implies rooting Android phones, unfortunately).  I have no experience with
Mobile IPv6, and don't know whether it's implemented.

-- Juliusz