Messages in this thread |  | | Date | Fri, 7 Sep 2001 02:47:46 +0100 | From | Jamie Lokier <> | Subject | Re: notion of a local address [was: Re: ioctl SIOCGIFNETMASK: ip alias bug 2.4.9 and 2.2.19] |
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H. Peter Anvin wrote: > 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.
Nice. Gives false negatives in some cases (e.g. a local tunnel) but that doesn't really matter.
I've considered this technique for deciding whether it's safe to use the MIT-SHM extension with X:
Open a SHM segment; write fairly secure random data into it; ask the X server to connect to that segment and read it back as an image over the X protocol; check whether they match.
If the X server reports an error, it's remote. If it finds a SHM segment it may still be remote, hence the random data check.
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