Whoa; the 3 network?

Henry Steuart jhs at ueno.egenius.org
Thu Dec 25 20:35:19 UTC 1997

A bit behind on mail owing to the pressure of not shopping early enough but
(while I'm waiting for the turkey to cook), having read through the whole
thread to date, I couldn't resist a comment on the statement below...

At 10:13 PM 12/23/97 -0500, you allegedly wrote:
>Right, but since each border router off of the public Internet can't 
>advertise anything smaller than /24 (would *your* router accept an 
>advertisement for, each seperate office needs at least a /24.
>Yeah, NAT can take care of the internal addressing, but you're still stuck 
>with the fact that you "only" can have 256 seperate border routers.
[snip for brevity]

Just where are the "border routers" connecting to?  Thanks to smd and
others (in reaction to the table growth and flap frequency) a couple of
years ago many places on/in the net will not advertise/accept anything less
than a Classful C /19 (in certain ranges, granted) and will not accept
anything longer than a /16 or /8 from "classful" B or A networks.  This
eventually matched the RIPE rules for address allocation - nothing longer
than a /19 from RIPE.  Sprint published their rules (here on NANOG and
elsewhere) and others worked on roughly the same set.  The rules haven't
changed much!!  Ergo - if your prefix is long you won't be routed!

e.g. /8 (or even a bit longer maybe) should be reachable but /25 will probably not!  However should be reachable
internally via wherever /8 is advertised.

If you have a small site connected only via the public net (i.e. to an ISP)
you need to get a routeable address space from YOUR UPSTREAM PROVIDER from
their address block!! (note:- if you _are_ the provider you will obviously
be aggregating to avoid the flaps/entries issue so this doesn't affect you
- you reach your internal hosts via your IGP tables!!).  

If you want the flexibility to change providers when they scr*w up [they
will :-) ] then you need a private address space behind a NAT-type device
and then get a /32 from "NE1-the-ISP.com".  Renumbering a single host is

How GE deal with things is their headache for now, but with the filtering
rules above and the renumbering necessary to get small sites routed in
public it strikes me that it would be more sense for them to renumber ONCE
into the space and use NAT or something similar to fake-out the
IPV4 routing. 

It doesn't take a rocket-scientist to work out that unused IPV4 space (i.e.
space not populating public routing tables) will at some future time become
reclaimed either by default or, as elsewhere suggested, by being traded as
a commodity.  Of course, IPV6 becomes the lazy way out - "there'll be
plenty of addresses for everybody" (deja vu?) - if/when it arrives!

Something to ponder over dinner.....

Have a good (insert relevant reason for celebration here) holiday.

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