> From: Lsr <lsr-boun...@ietf.org> On Behalf Of David Lamparter
> Sent: Wednesday, November 9, 2022 10:45 AM
> Hi Peter, hi all,
> 
> 
> to iterate on the comment I made on the mic a few minutes ago, I
> apparently have a rather different understanding of existing IS-IS
> behaviour.  Reading 5305/5308,
> 
> ...                     "if a prefix is advertised with a metric larger
   > than MAX_V6_PATH_METRIC (0xFE000000), this prefix MUST not be
   > considered during the normal Shortest Path First (SPF)
   > computation."
> 
> A prefix that is "not considered" is not an unreachable prefix.  It's a
> prefix that is in the DB but ignored entirely, as if it wasn't there at
> all.  A less specific prefix may cover it, and I would expect that to
> work normally.

+1
 
> The UPA draft is changing this such that now some values may mean that
> the prefix is in fact unreachable. 

+1


> I'd rather not do that and just add
> a sub-TLV for it.

I'm fine to use max_prefix as per RFC 5305 (prefix not considered during SPF) 
as this allow for incremental deployment.
But in my opinion, advertising the unreachability semantic requires an 
additional explicit signaling. (I'm proposing a prefix flag, but that seem like 
a detail at this point)

Thanks,
--Bruno

> 
> (Alternatively, if I misunderstood 5305/5308 - I'm pretty sure I'm not
> the only one to read it that way and that's a pretty important
> errata?!?)
> 
> Cheers,
> 
> 
> -David
> 
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