Re: [GROW] WGLC: draft-ietf-grow-ops-reqs-for-bgp-error-handling-04

["White, Russell" <[e-mail]>]

>> o  AS1 is advertising 192.0.2.128/25 to both AS2 and AS3.
>> o  AS2 is advertising both 192.0.2.128/25 and 192.0.2.0/24 into AS4.
>> o  AS3 is advertising 192.0.2.128/25 into AS4
>>
>> I am afraid you are too optimistic :) 
>>
>> Actually, this is really simple to fix in one of two ways.
>>
>> First, AS4 could see the overlap on the outbound side, note the
>> origin AS is the same, and set the longer prefix to NO_EXPORT.
> 
> I don't think this is as simple as this ... Remember that when the less
> specific (/24) goes away the AS4 must readvertise the more specifics not
> to break routing. So therefor I do not think that any simple policy
> would work. The choice/decision what to advertise and what not must be
> done at best path run.

Sure --but won't best path be run when the best path towards a specific destination falls out of the table?

>> Alternatively, the BGP implementation in AS4 could be modified so
>> that when running bestpath if a losing route has a specific
>> community, it is transferred to the winning route. This would allow
>> the winning route to gain the BOUNDED community in processing.
> 
> Actually I am not that clear I understand this business reg communities
> marking. How about we consider even much simpler and ASBR local solution:

A local ASBR only solution won't work for various reasons, so let's not. :-)

> If this is PI address given to a customer I actually do not know any ISP
> who would advertise his smaller blocks in addition to his aggregate
> those blocks are taken from. Only for backdoor/multihoming the smaller
> blocks get advertised via some other ISPs, but never directly connected.

So what you are saying is that if a provider owns 10.1.0.0/16, and gives out 10.1.1.0/24 to a customer to advertise through some other provider the customer is connected to, the provider would never advertise 10.1.1.0/24 as well as 10.1.0.0/16? Why not? Since the longest match always wins, what you're saying is that the provider that handed out the address space would end up routing through the competing provider (the customer's other provider) to reach the customer, because there is a longer match being advertised by the customer through the competing provider.

That doesn't make any sense to me.

> Just to be very clear .. VA (any of the VA drafts) does not talk about
> the same problem. For one it does not stop BGP from advertising anything
> and second it is intra-domain solution.

Right --the VA drafts increase stretch and don't reduce the total table size for anyone. In return, you must inject a good bit of complexity, and consider the various problems involved with routing traffic on a smaller number of links through your network. 

I prefer the simpler solution. And yes, it is simpler, even if it doesn't solve (outright) every possible problem in the space.

:-)

Russ