Re: notion of a local address [was: Re: ioctl SIOCGIFNETMASK: ip alias

[H. Peter Anvin]

Followup to:  <[e-mail]>
By author:    [e-mail] (Wietse Venema)
In newsgroup: linux.dev.kernel
> 
> The SMTP RFC requires that user@[ip.address] is correctly recognized
> as a final destination.  This requires that Linux provides the MTA
> with information about IP addresses that correspond with INADDR_ANY.
> 
> I am susprised that it is not possible to ask such information up
> front (same with netmasks), and that an application has to actually
> query a complex oracle, again and again, for every IP address.
> 

In autofs, I use the following technique to determine if the IP number
for a host is local (and therefore vfsbinds can be used rather than
NFS mounts):

connect a datagram socket (which won't produce any actual traffic) to
the remote host with INADDR_ANY as the local address, and then query
the local address.  If the local address is the same as the remote
address, the address is local.

	-hpa
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