David Stevens wrote:
Brian Haley <[EMAIL PROTECTED]> wrote on 12/18/2007 12:57:54 PM:
Trying to connect() to an IPv6 link-local multicast address by
specifying the outgoing multicast interface doesn't work, you have to
bind to a device first with an SO_BINDTODEVICE setsockopt() call.
Other OSes allow this operation, like FreeBSD, Tru64 UNIX and Solaris.
No, you simply have to specify sin6_scope_id for link-scope
addresses, like you do in unicast cases.
But isn't this why IPV6_MULTICAST_IF exists? So you don't have to bind
to an interface or use the scope id? RFC 3493 does not mention having
to set a scope id in order to send multicast packets:
IPv6 applications may send multicast packets by simply specifying an
IPv6 multicast address as the destination address, for example in the
destination address argument of the sendto() function.
Your patch requires them
to match (if specified), but I don't think IPV6_MULTICAST_IF should
override or require a match for a valid sin6_scope_id (or be an error).
The patch won't override sk_bound_dev_if, or sin6_scope_id, it's a last
resort for link-local multicast. As far as matching, I think they
should if you set both SO_BINDTODEVICE/sin6_scope_id and
IPV6_MULTICAST_IF. I can relax that check if you like.
The one thing my patch does do is set sk_bound_dev_if, which it never
did - that seemed like the right thing to do since that's what the scope
id path does, and makes sure we always continue to use this interface.
If I read it correctly, the existing code uses IPV6_MULTICAST_IF
if the sin6_scope_id is not set, otherwise honors the interface specified
in the connect. That seems like correct behaviour to me, and RFC 3493
doesn't address the relative precedence of the two that I see. This is
in the "linklocal" branch, and all unicast linklocal's require specifying
sin6_scope_id. Multicast doesn't if require a scope_id in the case where
you've done an IPV6_MULTICAST_IF, but it should still allow a different
scope_id when you have used IPV6_MULTICAST_IF.
The IPV6_ADDR_MULTICAST check is inside the sin6_scope_id if()
statement, so will never get checked if the scope hasn't been specified,
that's the bug. Since that isn't required for multicast we always get
an EINVAL here.
Do you have application code that you believe is correct that
doesn't work?
Yes, a customer does.
-Brian
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