Re: ? Re: [DNA] Individual Submission for DNA Best CurrentPractiJinHyeo

Greg Daley <greg.daley@eng.monash.edu.au> wrote:

Hi Erik,

Let's not go too far on this subject, since I think
we both believe that MAC addresses (in SLLAO and otherwise)
may not be a good identifier in general for detecting change.

Erik Nordmark wrote:
>>I think that where it makes sense to ensure that the MAC address
>>matches (for example, where it was available in previous messages,
>>in the SLLAO of an advertisement), then that's OK.
>
>
> Using the SLLAO content doesn't have the issues relating to looking into
> the L2 header for an L2 address, but I still don't see how using the SLLAO
> would help in detecting whether the link is the same or different.
>
> This is because the content of the SLLAO is not required to be globally unique:
> for some link layers the addresses might be local, and for other link layers
> it might be the case that a single router is allowed to use the same SLLAO on
> different interfaces.
>
> Thus receiving a RA with the same SLLAO as earlier is not indicating that
> the host is on the same link as earlier.
>
> Furthermore, since routers can come and go as well as change their
> link-layer address (or have multiple interfaces with different link-layer
> addresses for some load distribution across interfaces [latter is mentioned
> in RFC 2461]) the reception of a RA with a SLLAO content which has never
> been received before, is not an indication that the host is attached to a new
> link either.
>
> Since the SLLAO content can err in either direction (same when on different
> link, and different when on same link) it doesn't even seem useful
> as a hint pointing in any particular direction.

I think that the role which it plays in ND is appropriate,
in that changes of SLLAO cause the NC entry to be forced to
STALE.

This means that there's need for some check, possibly,
at some time in the future (after a delay, if the NCE is used,
and upper layer confirmation isn't available).

In the case where that occurs, then you'd probably have different
prefixes in any case, which you'd be listening to instead.

> The global prefixes assigned to a link is what is needed (until routers
> start advertising some form of link-id in the RAs) to make the determination.
> Once you do that I don't see how adding SLLAO into the mix would improve
> anything.

Indeed.

> Erik
>

Re: ? Re: [DNA] Individual Submission for DNA Best CurrentPractiJinHyeock Choi I Networking LAB Samsung Advanced Institute ofTechnologyResearch Staff Membe