Hi all, Out of curiosity, I've investigated Bird [0] to see if Babel could easily be implemented on top of it. It turns out it doesn't, the reason is detailed below.
Bird provides nice features for routing protocol programmers [1], such as a neighbour cache [2] or an events architecture [3]. Besides, the interface with the core is very well documented and looks quite clean. It turns out that implementing Babel would be quite difficult, because of a very questionable design choice: in Bird, IPv4 and IPv6 are *completely* separated. That is, you choose *at compile time* whether you want to use IPv4 or IPv6. It affects any structure, even the ip_addr structure. This means that you can't manipulate IPv4 addresses and IPv6 addresses at the same time — which Babel does: it uses link-local IPv6 for communicating with neighbours, while routes and next-hops can be IPv4 or IPv6 data. It's fine when the protocol is single-stack (old BGP, OSPFv2/v3 or RIP/RIPng), but not otherwise. For instance, dual-stack BGP is impossible with Bird, you need to run two distinct instances [4] — which is cumbersome. In the case of Babel, running two single-stack instances is not only cumbersome, but also difficult to implement, since we need IPv6 link-local even when working with IPv4 routes. I see multiple solutions for implementing Babel on Bird: 1/ Only implement IPv6 Babel. 2/ Since Babel can use IPv4 to communicate between neighbours (see Section 4. of RFC 6126), the IPv4 implementation could use that. However, it wouldn't be interoperable with all known Babel implementations (babeld and Quagga). 3/ Redefine all needed structures and use link-local IPv6 anyway, even when compiled for IPv4. This would be tedious, would require to bypass most Bird abstractions, and the resulting code would probably never make it upstream. If somebody wants to implement Babel on Bird, the most reasonable option seems to be 1/. It would certainly earn Babel the title of "post-modern routing protocol", but I'm sure some people will complain. Baptiste [0] http://bird.network.cz/ [1] http://bird.network.cz/?get_doc&f=prog.html [2] http://bird.network.cz/?get_doc&f=prog-2.html#ss2.7 [3] http://bird.network.cz/?get_doc&f=prog-8.html#ss8.6 [4] https://gitlab.labs.nic.cz/labs/bird/wikis/FAQ
pgpQ4fd7Uddyh.pgp
Description: PGP signature
_______________________________________________ Babel-users mailing list [email protected] http://lists.alioth.debian.org/cgi-bin/mailman/listinfo/babel-users
