Re: Pitfalls of annoucing /24s

["K. Scott Bethke" <scott () carpathiahost com>]

Hi Andy,

Verio says they accept old class-a space at the /22 orshorter level so that
isn't it.  I am fairly certain you can not successfully multihome with PA
class-A space..  If you are not announcing that /22 to AT&T then anyone that
is single-homed to AT&T (or preferring them) will probably not be able to
reach your /22.  I ran into this problem with some 4/8 space that Level3
assigned to me by mistake.  So you are dealing with more of a Policy issue
rather than general prefix filter.

-Scott

----- Original Message ----- 
From: "Andy Ellifson" <andy () ellifson com>
To: <nanog () merit edu>
Sent: Wednesday, October 15, 2003 6:28 PM
Subject: Re: Pitfalls of annoucing /24s


> 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 () 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.