[DNA] Re: Sending RS probe after link-change in simple DNA

[Suresh Krishnan <suresh.krishnan@ericsson.com>]

Hi Julien,
   Thanks for the comments. Please see responses inline.

Julien Laganier wrote:
> Folks,
> 
> I see two problems with the current behavior when sending RS probe with 
> simple DNA.
> 
> 1. Router creating a NCE for a global address belonging to a different 
> subnet:
> <snipped>
> ...
> Thus since a SLLAO is present but router2 has no existing NCE for the 
> host, router 2 will create a NCE for the global unicast address 
> prefix1::iid although prefix1 is not on-link and not advertized on 
> link2 by router2.
> 
> Isn't that a problem?

One of the requirements of Simple DNA is that the router support 
tentative options as defined in draft-ietf-dna-tentative-00.txt. So the 
RS will contain a tentative option (TO) instead of the SLLAO. And such 
option will not create a neighbor cache entry.

> 
> If it is that could be avoided by specifying that a simple DNA host MUST 
> source its RS probes from one of its link-local addresses.
> 
> 2. Problem of default router selection when moving in a NETLMM domain.
> 
> As you might know, when a host moves within a NETLMM domain, although it 
> may change attachment link, it will consistently receive the same 
> router advertisement in RAs sent by the NETLMM MAGs acting as default 
> router.
> 
> Let's suppose a host change from link1 to link2 served by MAG1 and MAG2. 
> With the currently specified behavior of a simple DNA host, if the 
> prefix is the same then the host should conclude it hasn't changed 
> link:
> 
>>   On reception of a Router Advertisement which contains prefixes which
>> intersect with those previously advertised by a known router, the
>> host utilizes the configuration associated with the detected network.
> 
> Thus after the link change the host will continue to use the 
> configuration valid on link1 where the default router is MAG1. However, 
> it is now attached to link2, where MAG2 should be the default router. 
> Since MAG2 and MAG1 might well have different link-local addresses and 
> MAC addresses. Thus, MAG2 will be added to the default router list but 
> won't be selected as default router instead of MAG1. This is going to 
> be a problem since host won't be able to send packets to its default 
> router MAG1. Thus connectivity for the host will be disabled until NUD 
> concludes MAG1 isn't reachable causing MAG2 to be selected as a new 
> default router.

The sentence above holds true only when an RA is received from a KNOWN 
ROUTER (i.e. one that has an entry in the SDAT). So this issue will 
occur only if MAG2 and MAG1 have the same link local AND MAC address ( 
in which case there is no real issue :-)

Thanks
Suresh