[arin-ppml] ARIN-prop-167 Removal of Renumbering Requirement for Small Multihomers

William Herrin bill at herrin.us
Mon Apr 30 18:26:59 EDT 2012

On 4/30/12, Jo Rhett <jrhett at netconsonance.com> wrote:
> On Apr 30, 2012, at 9:19 AM, William Herrin wrote:
>> Prefixes announced into BGP are expensive and everybody except the
>> originator bears the cost. For a decade limits were placed at /20 or
>> /22 in order to indirectly suppress the route count.
>> The policy which finally allowed access to /24's balanced this need by
>> requiring such /24's to be returned in order to get more addresses. It
>> was well understood that end users initially receiving a /24 would
>> encounter the grave difficulties associated with renumbering when
>> their address needs grew. This compromise was deemed better than
>> freezing them out of ARIN addresses entirely until they reached the
>> larger threshold size.
> While I agree with everything you said here, I want to raise a question.
> The point of these limits was to avoid the old routers hitting the 192k
> wall, and later the 256k wall. Three years ago everyone with routers that
> could only handle 256k routes hit the wall anyway. It's far past that time,
> and I really don't know of any production gear still operating in a
> defaultless mode which accepts less than a million routes.  Anyone with
> older gear is running crippled anyway, so we don't need to protect them.
> Have these concerns been obsoleted?

If you're running IPv6, your wall is short of 1M routes. I don't know
if that means 512k or 768k but the exact number is well short.

So, the wall has moved but only so far.

C & J could build the next generation of routes to 10M instead of 2M
if the demand was there. You can build a route processor that can keep
up and you can also build a TCAM that can hold it. It wouldn't break
the bank but it likely would double the cost. Fortunately, 10M is
enough to satisfy the maximum probable disaggregation of the IPv4
table in any scenario that doesn't involve widespread abandonment of
the /24 boundary.

However... if the demand pattern shifts too fast then C & J both could
be stuck without shipping product lines capable of supporting more
than about double the current IPv4 routing table or without enough
built product ready to ship. Somewhere around 150k mostly very
expensive routers have to be upgraded or replaced before we hit the
next wall. Could be dicey.

Short answer to your question: no, the concerns have not been obsoleted.

Bill Herrin

William D. Herrin ................ herrin at dirtside.com  bill at herrin.us
3005 Crane Dr. ...................... Web: <http://bill.herrin.us/>
Falls Church, VA 22042-3004

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