v6 deagg

William Herrin bill at herrin.us
Tue Feb 24 01:22:02 UTC 2015


On Mon, Feb 23, 2015 at 1:33 PM, Randy Bush <randy at psg.com> wrote:
> you might find http://www.route-aggregation.net/ interesting

Hi Randy,

I found it very interesting. Wish I'd noticed when it was fresh.

I don't fully understand the math yet but the algorithm doesn't smell
right. As near as I can figure it may only be correct in a static
system. If after convergence the disaggregate ceases to be reachable
from the aggregate, there doesn't appear to be either enough
information in the system or enough triggers traveling between routers
for it to reconverge to a correct state.

Deriving only from the information available to each router at each
step, look at page 58 in the presentation and see if you can figure
out what happens to the network in that start state when the link
between u7 and u9 drops. Remember that all the slashed half-moons mean
that the router in that position does not relay the disaggregate and,
in most cases, does not know that the disaggregate exists.

I've emailed the authors and asked them to clarify. I hope I'm wrong.
I'm tried of being a killjoy on this sort of thing and it would be
truly cool if it turns out they've cracked the problem.

Regardless, if we could presume (with support from the registries)
that disaggregates are always reachable from the aggregate (always TE,
never downstream customers or discrete sites) and everybody with an
address block was courteous enough to advertise an aggregate then it
might be usable to control IPv6 deagg. Actually, as long as we could
assume the first part we could probably have routers synthesize
aggregates to cover the second. But without the first assumption it
looks dysfunctional.

I discussed the cutouts problem in my 2010 presentation to ARIN XXVI in Atlanta:
https://bill.herrin.us/network/201010-cutouts.pdf

Regards,
Bill Herrin



-- 
William Herrin ................ herrin at dirtside.com  bill at herrin.us
Owner, Dirtside Systems ......... Web: <http://www.dirtside.com/>



More information about the NANOG mailing list