Added babel-users to CC.
During discussion about this the other night, I guessed at an admin distance of 100 for Babel. In conversation this morning with Don Slice he indicated that a number of 100 might be a bit low as that do we really trust Babel more than OSPF? Do people have opinions on what the Admin Distance should be set too?
Here are the real-world cases I know. Our Babel network here in Paris uses FRR on its edge routers, redistributing a default route from RIPng into Babel, and announcing a static route over RIPng to the rest of the universe. If there are two edge routers, we want the RIPng route to be used instead of the Babel route announced by the other edge router, so Babel must have a higher AD than RIPng. (My employer happens to use RIPng for IPv6 routing, but the same argument would apply to OSPF or IS-IS.) The Italian confederation of mesh networks uses a mixture of OLSR, BATMAN-adv and Babel in its individual meshes, and uses Babel for routing between the individual meshes (mainly due to the minuscule amount of traffic it generates as compared to the traditional mesh protocols). I'm not entirely clear how redistribution is done in the confederation, but I believe that they'd prefer Babel to have a lower AD than OLSR. The Slovenian mesh network (wlan-si) uses both Babel and OLSR. If a given prefix is carried by both Babel and OLSR, I believe that they prefer the Babel route. This, again, implies that Babel's AD should be smaller than that of OLSR. The Nexedi overlay network uses Babel for routing between LANs, mainly due to its ability to choose the best among a set of parallel tunnels. They don't do any routing within the LANs, so any AD will do for them. The above examples would seem to imply that Babel's AD should be between that of traditional IGPs and that of traditional mesh protocols. However, I don't see any reason why a deployment wouldn't use Babel to distribute externals between OSPF and IS-IS islands (e.g. in cases where Babel is being used to pick the best among parallel tunnels, as in Nexedi's case), so having Babel's AD lower than that of traditional IGPs would appear to make sense in some cases. -- Juliusz