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