Subject: [Sidr] draft-ietf-sidr-arch-00.txt

From: Iljitsch van Beijnum <[email-masked]>
Date: Wed, 21 Mar 2007 09:35:56 +0100

I was looking through draft-ietf-sidr-arch-00.txt and I noticed this:

5.2.2. Multi-homing

    If a multi-homed subscriber wants multiple ASes to originate routes
    for prefixes that it holds, then it must explicitly authorize  
each of
    them to do so by issuing a ROA for each AS in question.

Does this address the solution where multihomer M uses ISPs A and B,  
and M's prefix is injected into BGP by both A and B and NOT by M?  
I.e., "inconsistent origin AS", which is frowned upon.

If not, the text is unclear. If so, why is there no discussion of the  
normal situation where the multihomed AS advertises its prefix itself?

Same thing for portable allocations without multihoming, although  
there the situation where the ISP originates the prefix is more common.

BTW, it would be helpful if the availability of new drafts would be  
announced on the list with the draft name in the subject.

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From: Stephen Kent <[email-masked]>
Date: Wed, 21 Mar 2007 05:00:21 -0400

At 9:35 AM +0100 3/21/07, Iljitsch van Beijnum wrote:
>    for prefixes that it holds, then it must explicitly authorize each of

This text is saying that generation of multiple ROAs by M will allow 
A and B to both advertise M's prefix in a verifiable fashion, which 
should make this case less "frowned upon" :-).

>If not, the text is unclear. If so, why is there no discussion of 
>the normal situation where the multihomed AS advertises its prefix 
>itself?

If M originates the routes, i.e., M's AS number is the origin AS in 
advertisements, then only one ROA is needed, and it was not 
classified as "multi-homed" in the document. We will add text to make 
this distinction clear.

>there the situation where the ISP originates the prefix is more 

OK.

Steve

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From: Curtis Villamizar <[email-masked]>
Date: Wed, 21 Mar 2007 09:45:43 -0400

In message <[email-masked]>
Iljitsch van Beijnum writes:
>     If a multi-homed subscriber wants multiple ASes to originate
>     routes for prefixes that it holds, then it must explicitly
>     authorize each of them to do so by issuing a ROA for each AS in
>     question.
>  

If normal means "architecturally pretty" then the multihomed prefix
advertised by the true oridinator is normal.  No special case is
needed for that.

Many multihomed enterprises don't have their own AS and have a single
prefix.  They don't run BGP.  Instead each provider conditionally
originates the prefix on their end with their AS if the link is up.
If normal means "more common" then this might be the normal case.

Curtis

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From: Iljitsch van Beijnum <[email-masked]>
Date: Thu, 22 Mar 2007 09:44:04 +0100

> advertised by the true oridinator is normal.  No special case is

If you mention special cases you must also specify the normal case.  
These are engineering documents, any time someone has to think about  
semantics we're in trouble.

> If normal means "more common" then this might be the normal case.

Absolutely not. Last time I checked the first figure for incosistent  
origin AS were less than 1000 prefixes. The nature of this practice  
means you'll never see every affected prefix from any one given  
vantage point but it's pretty obvious that this is NOT a common  
practice.

And why sghould it be? An AS number is much easier to get than  
address space and running BGP is much simpler than alternative  
methods to inject/remove prefixes depending on connectivity to a  
particular ISP.

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From: Curtis Villamizar <[email-masked]>
Date: Thu, 22 Mar 2007 09:47:44 -0400

In message <[email-masked]>
> semantics we're in trouble.

OK.  I see your point.  IMHO Adding mention of the normal case would
be a better fix than removing this text.

The remainder of this thread is an aside to the discussion of whats in
the draft and so can be disregarded.

> vantage point but it's pretty obvious that this is NOT a common  

Good.  Seems less common than it used to be.

> methods to inject/remove prefixes depending on connectivity to a  

I suppose my observation of this trend is severely dated and no longer
valid.  Dating myself again.  Enterprises used to have an easier time
getting PI space and they didn't trust the Internet so some wanted
multiple providers.  Though there was no evidence that multiple
providers yielded higher availability that two circuits to the same
provider.  In fact the opposite was true since the provider bought the
circuits and with same provider they could insist on diverse paths
(and not always get it, but always get charged for it).

Curtis