Subject: Re: [RPSEC] Back to the Basics: The AS Path

From: Sandy Murphy <[email-masked]>
Date: Mon, 24 Jan 2005 15:35:19 -0500 (EST)

>The trick is that it works for one specific AS and not the Internet in
>general.  If I insert provider Xs AS in the AS path they will reject the
>announcement.  No one else will reject it.
>
>I don't know of another knob that can do this...

Not send them an announcement at all?  Really, I don't get this.

--Sandy

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From: Blaine Christian <[email-masked]>
Date: Mon, 24 Jan 2005 16:04:03 -0500

> Not send them an announcement at all?  Really, I don't get this.

Ahhh, you see the problem is that you are not directly connected to that AS
yet you do not want them to see your prefixes.  You can not specifically
block announcements through every OTHER network to that network.  The only
way to do it is to force the loop check.

*_a___b___c___d
      |       |
      |___e___f

If you do not want "d" in the above graph to install a prefix the use of
loop free routing as a kludge becomes necessary.  Otherwise you would have
to block b's outbound to c and to e.

BTW, I am getting initial responses from the operator community where folks
are saying that they prepend inbound advertisements with that, specific,
peers AS.  This case still seems to fit in with the compression of like AS
numbers into "one" instance of an AS for the purposes of identity.

Regards,

Blaine