On 02/10/15 15:32, Justin Wilson - MTIN wrote:
I was in a discussion the other day and several Tier2 providers were talking about the idea of adjusting their BGP filters to accept prefixes smaller than a /24. A few were saying they thought about going down to as small as a /27. This was mainly due to more networks coming online and not having even a /24 of IPv4 space. The first argument is against this is the potential bloat the global routing table could have. Many folks have worked hard for years to summarize and such. others were saying they would do a /26 or bigger.
However, what do we do about the new networks which want to do BGP but only can get small allocations from someone (either a RIR or one of their upstreams)?
Any RIR - or LIR - that considers allocating space in sizes smaller than a /24 (for the purpose of announcing to the DFZ) would do well to read this report from RIPE Labs: https://labs.ripe.net/Members/emileaben/has-the-routability-of-longer-than-2... tl;dr: it's still a bad idea to allocate smaller than a /24. On top of this, I've recently seen some figures that put a 'regular' BGP table mix, at over half of the prefixes received (from numerous upstreams) as being /24s. I really don't want to see everyone already de-aggregating their /18s to /24s, to then go and de-aggregate down to /27s instead. Whilst getting routers with *big RIBS* for little monies, is easy (i.e. Linux box + Quagga). Getting routers that have all the features SPs need, with the throughput requirements too, /and/ have plenty of *FIB* space - that's expensive. Super expensive. -- Tom