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Re: aggregation & table entries
- From: bmanning
- Date: Wed Oct 13 16:26:48 2004
On Wed, Oct 13, 2004 at 12:54:44PM -0700, Kevin Oberman wrote:
> > Date: Wed, 13 Oct 2004 18:43:45 +0000
> > From: firstname.lastname@example.org
> > Sender: email@example.com
> > > > or... why do people insist on injecting routes to non-existent
> > > > things? a route table entry is a route table entry, regardless
> > > > of the scope.
> > >
> > > Is this where you advocate that providers only announce the parts of
> > > their assigned blocks that are in use?
> > seems like a good lead in, so yes - i advocate folks only
> > announce what they use. may play old-hob on the ISP that
> > likes to use some other metric for accepting announcements,
> > (e.g. RIR or other routing registry DB) and will no doubt
> > increase the tension on justification of proxy announcements,
> > but overall, this seems to be a good goal.
> First, we do accept prefixes from most ASes based on RIR.
good traditional thinking .... requireing me to announce the
whole /20 when all i'm using is a /27... after all, its just one
routeing table entry... why should you care? :) (playing straightman)
> Second, we don't simply assign address space sequentially from our
> assigned spaces. We have an addressing plan that leaves the assignments
> deliberately sparse to allow for better management and the ability to
> keep our PA assignments to a site contiguous. To only announce the
> active space would increase the number of routes we announce by about
> 80%. If everyone did this, the routing table would increase
> massively. So would the time to compute the routes which might lead to
> some really bad instability for some routers.
so -IF- everyone followed your internal address assignment policies,
scattering used space in a sparse matrix throughout the allocated pool,
then announing a single prefix (the aggregate) makes sense. Of
course this leaves you w/ lots of space that is useful for forging
as valid source addresses. (we'll even leave DHCP pools out of the
discussion - for now) so it would make sense for you to announce
the aggregate - since you use "random" bits throughout (nice marbling!)
but for those folks who use a more compact internal representation,
is there a good reason to reject their /27 instead of the larger /20
that has been allocated?
> > thanks for letting me rant. :)
> Any time, Bill.
I'll try and use it wisely