/27 the new /24

Tom Hill tom at ninjabadger.net
Fri Oct 2 16:33:50 UTC 2015

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:


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.


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