Re: [RRG] map change due to a path failure?

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

On 2008-03-26 15:09, Scott Brim wrote:
...
> On 3/25/08 5:54 PM, Brian E Carpenter allegedly wrote:
>> On 2008-03-26 03:49, Xu Xiaohu wrote:
>>> How about having the authoritative ETR to update the status of the
>>> EID->RLOC
>>> mapping in the mapping system automatically according to the
>>> connectivity
>>> between the ETR and the site network, while having the routing system to
>>> determine the reachability of the ETR?
>>
>> However, we want to avoid map flapping by design (you will remember
>> that BGP4 route flapping was a big problem).
>>
>> I would set a quite different timescale for status updates
>> in the mapping system - if we followed your suggestion, I would
>> suggest that a loss of connectivity should persist for
>> a long time, maybe 30 minutes, before the ETR changes the
>> map. I'd expect BGP to handle any outages on a shorter timescale.
>> If we set the timers in the mapping system to the same order
>> of magnitude as those in the routing system, we're likely
>> to see some horrible interactions between map flapping
>> and route flapping.
> 
> The current LISP trick is the "locator reachability" bits piggybacked on
> data packets.  You can separate operational changes (the kind subject to
> flaps) from configuration changes.  There is no need for mappings to
> change due to operational problems, nor timers etc.  I still don't
> understand why you think BGP would be involved.  Are you presuming that
> we are going to run BGP between nodes that are not globally routed?  Why
> would DFZ BGP even know that an ETR was dead?

Right. I was momentarily confused by the scary idea of
connectivity failures at the edge resulting in map updates.
I don't think the reachability bits are a trick - it seems
to me essential to separate short-lived connectivity
failures from long-term topology changes.

    Brian

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