Garrett Wollman wrote:
> In article <[EMAIL PROTECTED]>,
> Martin Burnicki  <[EMAIL PROTECTED]> wrote:
> 
>> AFAIK ntpd has to manage the binding to interfaces at least if autokey is
>> enabled since the signature hash also includes the IP address of the
>> interface via which a packet is sent.
> 
> At least some operating systems (don't know about Linux) allow this to
> be controlled using a control message.  For example, from the FreeBSD
> 6.3 ip(4) manual page:
> 
>      The source address to be used for outgoing UDP datagrams on a socket that
>      is not bound to a specific IP address can be specified as ancillary data
>      with a type code of IP_SENDSRCADDR.  The msg_control field in the msghdr
>      structure should point to a buffer that contains a cmsghdr structure fol-
>      lowed by the IP address.  The cmsghdr fields should have the following
>      values:
> 
>      cmsg_len = sizeof(struct in_addr)
>      cmsg_level = IPPROTO_IP
>      cmsg_type = IP_SENDSRCADDR
> 
>      For convenience, IP_SENDSRCADDR is defined to have the same value as
>      IP_RECVDSTADDR, so the IP_RECVDSTADDR control message from recvmsg(2) can
>      be used directly as a control message for sendmsg(2).
> 
> The IPV6_PKTINFO message is used for analogous functions in IPv6.
> 
> -GAWollman

We are aware of sendmsg(), recvmsg() and friends. The problem, however, 
is that there are many platforms that do not support this yet. It's a 
major effort to deal with this.

Danny
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