Subject: [Anima] GRASP and renumbering: suggestions and a question

From: Brian E Carpenter <[email-masked]>
Date: Tue, 31 May 2016 14:16:59 +1200

Hi WG,

I expect you saw the recent messages about renumbering, and you may
have seen the big discussion in 6man about stable addresses.

I think we are clear that address stability for the autonomic
infrastructure is very desirable, but the fact remains that in IPv6
addresses can always change, so GRASP needs to tolerate that.

After a little discussion on the design team list, I have two suggestions
for GRASP, and a question for the WG:

1) In the description of discovery, we need to say more about
the discovery cache timeout

 After a GRASP device successfully discovers a Discovery
 Responder supporting a specific objective, it MUST cache this
 information.  This cache record MAY be used for future
 negotiation or synchronization, and SHOULD be passed on when
 appropriate as a Divert option to another Discovery Initiator.
 The cache lifetime is an implementation choice that MAY be
 modified by network Intent.

I suggest adding something more here:

 In some environments, unexpected address renumbering might occur.
 In such cases, the cache lifetime SHOULD be short compared to
 the expected address lifetime and a mechanism to flush the
 discovery cache SHOULD be implemented.

2) We should also add something to the API, to allow an ASA
to optionally flush previously discovered locators.

Now the question. Should we add a TTL to discovery responses?
It isn't very hard to do.

Pro:
 - This would allow discovery cache timeouts to be tailored
   per ASA instance instead of per network.

Con:
 - It slightly expands the Discovery Response message.
 - It adds minor complexity to the discovery cache handling.

Comments? Opinions?

   Brian