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Re: Anyone notice strange announcements for
From: "Patrick W. Gilmore" <patrick () ianai net>
Date: Tue, 13 Jan 2009 13:20:48 -0500

On Jan 13, 2009, at 1:11 PM, David Barak wrote:
--- On Tue, 1/13/09, Patrick W. Gilmore <patrick () ianai net> wrote:

        Personally, I would be upset if someone injected
a route
with my ASN in the AS_PATH without my permission.

Why?  Is this a theoretical "because it's
ugly" complaint, or is there a reason why manipulating
this particular BGP attribute in this particular way is so
bad?  Organizations do filtering and routing manipulation
all over the place.  Is there something worse about doing it
this way than others?

Filtering and other manipulation happened on your router,
prepending my ASN is putting that information into every
router.  That seems to be a serious qualitative difference
to me.  Do you disagree?

This is qualitatively similar to an ASN announcing de-aggregated routes - it may be nice if they don't, and you don't have to accept them, but are they permitted?

No it is not. You own the prefix in question, so you own the deaggregates of it. You do not own the ASN in question.

That you do not see the difference explains a great deal.

This thread has been interesting & educational.  So
many people seem to be happy to explain why they should be
allowed to use globally unique identifiers they do not own
in ways which were not intended, then explain to the people
who do own those identifiers how they should react, which
alarms should go off, and even which priority the alarms
should have.

As I have repeated probably hundreds of times: Your
network, your decision.  I have yet to hear a credible
argument against that stance.  What you do _inside_ your
network is _your_ decision.  When it leaves your network,
however, things change.

Exactly! Provider RB announces $WEIRD. A bunch of providers receive alarms about the existence of $WEIRD, and they treated this as $IMPORTANT. The bunch of providers who treated this as $IMPORTANT are informing all of us about their monitoring thresholds and their responses to this threshold being met. Their networks, their decisions.

Wow.  Just .. wow.

"Exactly, even though I do something with your resources, announcing to the whole world, that cause you issues, you shouldn't tell me about because the alarms are inside your network."

Again, this explains a great deal.

It should be pointed out that pre-provisioned AS_Path filters and prefix-lists would actually be effective at defeating this and preventing someone who is actually malicious from using this technique. This is an excellent argument for implementing SIDR...

Finally we agree. Although I am not certain SIDR is the optimal answer, we agree it would solve the problem.

Announcing an ASN which is not yours to eBGP peers means it
is leaving your network, which means it is not just your
business.  Doing so and then telling the ASN owner that they
should not worry about it afterwards - and in fact arguing
when the owner repeatedly tells you this caused them
problems - does not seem to be the proper course of action.

Understood, but if this is viewed as problematic, there is a very simple solution: don't allow a BGP customer (or peer!) to prepend someone else's ASN.

How do you suppose I stop Randy from prepending my ASN?


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