Re: [RRG] getting rid of longest match

[Brian E Carpenter <brian.e.carpenter@gmail.com>]

On 2008-02-26 15:38, Danny McPherson wrote:
> 
> On Feb 25, 2008, at 7:06 PM, Tony Li wrote:
>>
>> If I understand this proposal, then for any given prefix, the entire
>> net would agree on a prefix length and only propagate paths for this
>> prefix length.  This would imply that there would actually be no
>> required hardware change, as all of this filtering could (and should)
>> happen during BGP processing (specifically during UPDATE parsing) and
>> prior to RIB insertion and thus prior to the FIB insertion.
>>
>> Thus, from a hardware perspective, this is largely a NOP.
>>
>> Note that this could somewhat decrease the complexities of future
>> hardware designs.  Since we now guarantee that there are no
>> overlapping prefixes, the table now effectively forms a tree of
>> variable prefix lengths, but now the first match found in the tree
>> suffices.  In the grand scheme of things I would judge this not to
>> have a significant impact, but it is arguably simpler.
> 
> Of course, this doesn't address the problem that spawned his
> query, which is someone else advertising my address space.
> 
> Today this sorta happens in a reactive manner, right?  For
> example:
> 
> o YouTube announces a /22
> o Someone announces a /24 of that /22
> o YouTube responds by announcing a /24 && /22
> o YouTube still largely broken
> 
> Cisco's still announcing /24s for prefixes which this happened
> to a decade ago.  The result is that things are only half broken,
> not completely broken, I guess.
> 
> The problem here is simply that of a reliable authenticated
> authoritative data source for who owns what - AND operators
> employing that to define routing policies.  If protocols like SBGP
> or soBGP want to build upon that and actually get some traction
> in deployment, great, but the egg here [1] is the data source that
> still doesn't exist.
> 
> [1] http://www.cnn.com/2006/TECH/science/05/26/chicken.egg/

All in all, it's hard for me to imagine a smooth path from
here to a world in which punching holes in arbitrary aggregates
isn't an unavoidable business requirement. So even if the
sort of agreement Iljitsch has in mind could be reached,
I'm certain it would contain exceptions...

   Brian

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