Pitfalls of annoucing /24s

Wed Oct 15 22:28:45 UTC 2003

I have a /24 allocated to my by XO Communications in Phoenix, AZ
(67.X.X.0/24).  I am currently announcing it to Verio in Europe.  A
friend of mine that is an XO customer in Phoenix with BGP to XO can get
to that address block within XO's network.

But on the flip side.  I also have a /22 from AT&T (12.X.X.0/22).  When
I announce that network block to Verio in Europe (and nowhere else),
only certain places get to the Europe location.  Networks that prefer
AT&T go to AT&T's network and die since the route isn't there.  I don't
know if I am missing something but it think it may have to do with how
the network's peering/filter schemes work.

I may just be walking around the problem since I am a transit customer
of Verio and they normally filter.

-Andy

--- Phil Rosenthal <pr at isprime.com> wrote:
> 
> On Oct 15, 2003, at 5:24 PM, H. Michael Smith, Jr. wrote:
> 
> >
> >
> > What about the /24's that many ISPs (especially tier 2-3) are
> assigning
> > to multi-homed customers?  What about an IX or "critical
> infrastructure
> > providers" that may be issued a /24 from ARIN (Policy 2001-3)?
> >
> As long as it's provider assigned, and your provider announces the 
> supernet that the /24 is from, it will still work.  If you announce
> PI 
> space out of the old class A space in /24's, many networks wont be
> able 
> to reach you.
> 