[dev] Babel Admin Distance

[Don Slice]

I agree that both OSPF and ISIS have better loop prevention techniques for
external routes, but don't at all remember a reason to have DV lower than
LS to make loops less likely.  For example, RIP has a higher AD that OSPF.
  I'm fine with whatever the group decides, since I don't really have any
compelling arguments either way.

On Wed, Sep 13, 2017 at 8:16 AM, Russ White <russ at riw.us> wrote:

>
> > 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
>
>


-- 
Don Slice
Cumulus Networks
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