North American Network Operators Group

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Re: ISPs Blocking Private Addresses?

  • From: Jay R. Ashworth
  • Date: Mon Feb 09 19:30:23 1998

On Mon, Feb 09, 1998 at 02:42:19PM -0600, Joe Shaw wrote:
> Most people use what's commonly refered to as Martian filters to filter
> out private address spacing.  It allows those ISPs to use private address
> space internally and not have to worry about advertising them via external
> routing protocols and also keeps them from accepting bogus route
> announcements from other providers who haven't used the filters.

There's an important distinction to be made, Joe, betwen filtering
_packets_ and filtering _announcements_.  Martian filters usually
filter packets.  What you announce, and what you send, need not have
anything to do with one another.

> > Do the "default-less" ISPs filter private addresses or do they let
> > routing/forwarding do the work?
> Default-less?

Yes: backbones whose routers have no default place to send packets not
handled by some explicit route.

-- jra
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