Hi Keiichi,
NOTE : [ Julien's address change: [EMAIL PROTECTED] ]
>
> I have one question about the usage of IPV6_PREFER_DST_LARGESCOPE and
> IPV6_PREFER_DST_SMALLSCOPE socket options.
>
> I'm afraid I cannot imagine when I need to use the above socket
> options, since selection of a destination address is done by
> getaddrinfo() (or by specifying an address explicitly) I think.
>
> Do you have any concrete idea of the usage of above socket options?
The idea is to use both IPV6_PREFER flags in conjunction with corresponding
AI_PREFER_* flags in getaddrinfo().
RFC3484 Destination address selection rule #8 ( prefer smaller scope):
Thus, IPV6_PREFER_DST_SMALLSCOPE is the default setting for a system.
One example might be that if sender wants to use global destination
address to talk to an onlink node for which it knows a smaller scope
address. In that situation, setting LARGESCOPE
socket option and passing AI flag to getaddrinfo() is recommended.
Now, for DST flags, it may be possible to get away with AI_PREFER_* flags,
but, implementations may vary in implementing getaddrinfo() for collecting
potential source addresses (RFC3484 section 8).
Hence for portability and consistency reason, both setsockopt() and AI flags
are recommended for destination scope.
>From implementation point of view do you think IPV6_PREFER_DST_*SCOPE
is redundant across all systems ?
Thanks,
-Samita
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