aggregation & table entries

Wed Oct 13 20:24:09 UTC 2004

On Wed, Oct 13, 2004 at 12:54:44PM -0700, Kevin Oberman wrote:
> > Date: Wed, 13 Oct 2004 18:43:45 +0000
> > From: bmanning at vacation.karoshi.com
> > Sender: owner-nanog at merit.edu
> > 
> > 
> > > > 	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

--bill