Re: [lisp] Some basic questions ...

[Marc Binderberger <[e-mail]>]

Hello Dino,

there was another question I forgot regarding the notifications: so 
when the map-notification is not used as an ACK for map-register but is 
actually informing the ETRs about events then how is the delivery 
guaranteed? The underlying IP/UDP transport may drop.

For map-register we periodically send again, so packet loss of 
map-registers is not a big problem. What is your idea for map-notifies? 
Some of the notifications may be singular events. Other of course could 
be periodic (e.g. merge notification triggered by the map-registers?).

Would I need an ACK for the map-notification (and some fast-timer 
re-send, e.g. every 1sec until ACKed) ?  That would take state/timer, 
although only until's it's ACKnowledged.


Thanks & Regards,
Marc



On Mon, 17 Feb 2014 10:13:16 -0800, Dino Farinacci wrote:
>> Hello LISP experts,
>> 
>> have two questions, mainly to understand the context a bit better.
> 
> No prob Marc. Thanks for the email. I'll attempt to answer them but 
> others can chime in as well.
> 
>> Q1: map-notify message.
>> 
>> maybe it's the name but I always expected this message is for the Map 
>> Server to inform ETRs. Kind of a "push" method. But reading RFCs 6830 
> 
> That is exactly what it is. It is used as a event notification from 
> the Map-Server to the ETRs that register for a particular EID-prefix. 
> So when a locator-set changes, the old locators can be notified. The 
> main reason to call it a "Map-Notify" was for this purpose. And you 
> can now understand why by looking at the data-center use-case 
> documents that have been published by Yves and Victor.
> 
>> and 6833 again it seems that the Map-Notify is simply an ACK for a 
>> received and processed Map-Register message. Take the Map-Register 
>> message, set the type to Map-Notify and send back.
> 
> So when a registerer requests Map-Notifies, it will get them for 
> various reasons. The first is the case I said above and the other 
> case is to acknowledge a Map-Register.
> 
>> Now, the use as ACK is not a contradiction to the broader use as a push 
>> message. So my question to the LISP experts and inventors is: is 
>> Map-Notify restricted to be just an ACK? (having an extra type for it 
>> seems generous)
> 
> It is not restricted to just an ack. There is also another use case. 
> Here it is:
> 
> (1) You have two xTRs, each sitting behind different NAT devices.
> (2) The xTRs get private addresses assigned to their interfaces. So 
> they are using them as "local RLOCs". But no one will be able to 
> encapsulate to them so they need to find out their global RLOC 
> addresses.
> (3) Each of the two xTRs are at the same LISP site and can receive 
> encapsulated packets for the same EID-prefix.
> (4) When they each discover their global RLOCs (by mechanisms 
> descrbied in draft-ermagen-lisp-nat-traversal), they each register 
> their own global RLOC. They register with the "merge-request" bit set 
> so the Map-Server will add both xTR global RLOCs to the locator-set.
> (5) So now, if an xTR gets a Map-Request, it will want to send a 
> Map-Reply with the merged-locator set. Well how will it do that when 
> it only knows its own?
> (6) A Map-Notify is used here by the Map-Server to tell each xTR 
> about the other's global RLOC.
>