North American Network Operators Group

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Re: Class B address routing

  • From: Brandon Ross
  • Date: Thu May 18 21:01:05 2000

On Thu, 18 May 2000, Kenji Anzai wrote:

> I'm having problem with our class B address.  Last month, we tested our
> class B address.  We announce the address as 2 x /17 from 2 different
> POP under the same ISP's data center.  However, some ISP do NOT accept
> our route since the address belongs to traditional Class B address, and
> they told me that they only accept if we announce it as /16. (They
> filtered out our route…..) 
> I talked to some people, they suggested me that we need to announce the
> block as /16 from both POP, even though we only like to announce /17
> from each POP (Front /17 from one POP, the other /17 from another POP.). 
> How could we do so ?  Please help us.

At both POPs, announce the /16 normally.  Then also announce the specific
/17 as a non-export route.  The effect will be that the /16 will be
announced to the world so those ISPs that filter will listen to the
announcement.  Your upstream ISP will have both /17's so they will direct
the traffic within their network to the appropriate POP.  An added benefit
of this configuration will be that if one of your POPs goes down, the
traffic will automatically re-route to the other POP.

Brandon Ross                                                 404-522-5400
VP Engineering, NetRail                  
AIM:  BrandonNR                                             ICQ:  2269442
Read RFC 2644!
Stop Smurf attacks!  Configure your router interfaces to block directed
broadcasts. See for details.