[Babel-users] Kernel metrics/route redistribution

[Juliusz Chroboczek]

> One thing I don't understand: why is the priority multiplied/divided
> by 256 going into and out of the kernel?

This gives you a priority that is the default wireless hop count
(assuming lossless links).

> RTA_PRIORITY attributes appear to be a unsigned 32-bit int for both
> IPv4 and IPv6, which is more than enough to contain Babel metrics
> unmodified.

I recall having problems with priorities larger than 255, but that may
have been under BSD, I don't remember.

> I believe I can accomplish my goals by redistributing Babel into OSPF,
> not the other way around,

Then, if you're careful with how you map your metrics, you should be
fine -- you should have transient loops only.

> The only loops I can think of involve cases where a prefix falls off
> the network entirely, but that affects all Babel networks with
> overlapping announcements (e.g. default routes),

That's worked around by a hold time -- see Sections 2.8 and 3.5.5 of the
draft.

> Regardless, ospf6d announces external routes it learns from zebra as
> type 5 LSAs, and with a route map to set them to type 2 metrics, the
> Zebra route object's metric is copied into the announced cost. So,
> once I figure out where I'm losing metrics, we should be good.

Let me know if you want this patch to get into the trunk.  It's a little
bit more work, since we'll want the 256 factor to be user-configurable,
but I certainly have no objection to including it -- with a big, fat
warning in the manual page.

                                        Juliusz