Re: /25's prefixes announced into global routing table?

[William Herrin <bill () herrin us>]

On Fri, Jun 21, 2013 at 3:56 PM, Michael McConnell
<michael () winkstreaming com> wrote:
> As the IPv4 space get smaller and smaller, does anyone think we'll
> see a time when /25's will be accepted for global BGP prefix
> announcement. The current smallest size is a /24 and generally
> ok for most people, but the crunch gets tighter, routers continue
> to have more and more ram will it always be /24 the smallest size?

No.

1. Too many ASes whose operators are a part of too many cultures and
speak too many languages apply a blind filter at /24. Too hard to
change.

2. TCAM != RAM

However....

It is possible for a tunnel provider to:

1. Draw a covering route in to a well chosen set of data centers,
2. Set up a nice redundant set of tunnels from each data center to
each of its customers' Internet links,
3. Accept smaller-than-/24 routes at a higher priority than the
tunnels from its peers where those routes originate from the customers
to whom it assigned those addresses
4. Help the customers negotiate with the specific handful of ISPs that
operate the paths between them so that they'll accept the sourced
packets natively and propagate the smaller-than-/24 route within their
system.

It hasn't been done with any regularity, but it's technically
feasible, can be implemented within a few percent of optimal routing
and resilience and requires cooperation from few enough parties (all
of them directly paid) that it could happen if the economics were
right.


On Fri, Jun 21, 2013 at 5:15 PM, Grzegorz Janoszka <Grzegorz () janoszka pl> wrote:
> As the fragmentation will progress and we will be closing to the magic
> limit of 500.000, people will filter out /24 and then /23 and so on.
> Back to static (default) routing!

Don't bet heavy on that either. Many if not most of the Internet's
critical resources (think: DNS roots) sit within /24 announcements.
Incautious filtering shoots oneself in the foot.

Regards,
Bill Herrin


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