Hi Robert,

> Do you envision any form of aggregation to happen in the messaging between 
> ABRs (for both registrations and notifications) ? 


Well, as always, I try to generalize mechanisms and solutions. So while I don’t 
see an immediate need or benefit to it, I did write the protocol so that it is 
possible. I wasn’t comfortable with some of the implications of  non-host 
prefix liveness events, so I didn’t include those yet, but it is certainl 
possible. 


> I think the pub-sub model is really cool, but I am not clear what are the 
> advantages to do it in the IGP from ABRs vs BGP from area RRs (note that in 
> the latter case no new protocol is required). 


It doesn’t add more burden to BGP. It also doesn’t require BGP for those that 
aren’t using it. It might also be a bit faster than BGP as there’s less 
overhead.


> Also if we do it from local area RRs we do not need registrations - local RRs 
> know which next hops are attached to local service routes. And it would go 
> only where the service route goes. 


I think you’re asking if ABRs can be co-located with a client.  Yes, certainly. 
 An ABR could initiate a registration for its own purposes. I’ll add a 
clarification.


> Last I am a bit concerned with the scale here. If we keep registrations and 
> notifications at the atomic level the ABRs may need to keep pretty large RDB 
> and efficiently generate *targetted* notifications upon each local area node 
> transition or reception of notification from other ABR(s). 


Understood. You could also register for summaries, which would reduce the scale 
by an order of magnitude. Even without summaries, the RDB is pretty 
constrained. You have (# of local PEs) * (# of other area ABRs) + (# of remote 
PEs) * (# of local PEs).


> Last what protection would be in place to suppress the network wide meltdown 
> when client would (say by mistake or a bug) inject 1 million of registrations 
> ? Would that not result in a bit of load to all ABRs ? 


What protection exists if a BGP speaker injects a million prefixes? What 
protection exists if an IS-IS speaker injects a million LSPs? We can certainly 
add some protection mechanisms if people feel that it’s warranted. However, 
getting the right functionality first seems like a good starting point. Baby 
steps.

Tony


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