[dev] Babel Admin Distance

[Russ White]

> 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?

I don't tend to think of this as a matter of "trust," but rather just "we need to make an arbitrary decision in some places to keep things from blowing up." 😊 I would say that BABEL is a special purpose protocol, and I'd want to prefer the routes coming out of the ad hoc environment more than any possible "recycled" or "dual connected" routes coming out of what is likely to be the more fully connected "core" network. Of course, this isn't going to work in many SP environments, as eBGP might be on the "other side," but it "feels like" it would be better, in the general case, to prefer the BABEL route over the "normal" IGP route. 

This might actually argue for something lower than EIGRP, around 80, but I'll leave that question open for discussion...

The other argument that might bear on this discussion would be around routing loops -- BABEL doesn't have a lot of protection against them in a redistribution situation, I don't think, where OSPF and IS-IS seem to be much less likely to cause a routing loop in mutual redistribution situations. I don't remember why, but I always seem to think the DV having a lower AD than the LS helps prevent redistribution loops -- I would need to sit and work it out, but maybe Don might remember something here. 

😊

Russ