[lobster_johnson]

BGP looks really complex. Isn't OSPF (BGP's "little brother") a much attractive choice here? It's still complex, but should be much simpler.

Another attractive alternative to Flannel is Weave [1], run in the simpler non-overlay mode. In this mode, it won't start a SDN, but will simply act as a bridge/route maintainer, similar to Flannel.

[1] https://www.weave.works/products/weave-net/

[detaro]

BGP IMHO is much simpler than OSPF. No different area types, support for communities, no need to keep a link-state database for the entire network in all nodes, ...

[tptacek]

People keep talking about link state database overhead, but how significant is this in reality? The graphs we're talking about, even in huge deployments, are small.

If you're running etcd or consul, I'm not sure you retain the right to call LSA flooding "complicated". It's simple compared to RAFT!

[detaro]

Size probably doesn't matter that much until you start to fill entire datacenters, OSPF nowadays should work with hundreds of routers as well. Would be interesting to see how failure cases compare, if I remember right one of the arguments for BGP in data-center fabrics was that the updates following them stay more localized. (EDIT: a description how Microsoft uses it for really large networks, slide 11 talks about surges: http://www.janog.gr.jp/meeting/janog33/doc/janog33-bgp-nkpos...)

I find BGP easier to understand, and I don't see what benefit OSPF would have. (Not that I really have non-trivial experience with either, have only used them at home and toy networks)

[X-Istence]

Calico uses BIRD, and Calico just programs routes into the Linux kernel, BIRD then picks those up.

BIRD supports OSPF, so if you'd like to import/export routes using OSPF you can.