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NOTICE: This version of the NSF Unidata web site (archive.unidata.ucar.edu) is no longer being updated.
Current content can be found at unidata.ucar.edu.
To learn about what's going on, see About the Archive Site.
On 04/23/10 20:01, Chris MacDermaid wrote:
Mike, Port 111 is the sunrpc port. This is also know as the portmapper because it provides a mapping between available services and their ports. Port 111 isn't needed for LDM. From what I understand, a LDM client first tries to connect to port 388. If that fails the client then tries to connect using the portmapper service on port 111. In your case, it appears the connection on port 388 is failing for some reason.
The port-mapping part of Remote Procedure Call was an idea from the 1980s/1990s where, rather than being limited to TCP and UDP ports (64k of each) -- which were rapidly being eaten up with "known" services at the time -- you could just have a port mapper that would accept a connection on a single port (111), look at the requested service number (see /etc/rpc for examples), and then assign the connection a random port. Given that there were potentially thousands or millions of procedures that you might want to call on other systems, this was sort of mandatory.
NFS works this way and is still the bane of administrators. :-) Fortunately, most distributions allow you to "pin" the various NFS-related services to a specific port to make firewall configs simpler.
RPC, the whole thing, is still interesting, in that it allows exactly what it says: calling a procedure on a remote system. Lots more detail about RPC in Wikipedia but you'll also read that it's been mostly obsoleted by other, similar protocols.
As noted, the default for LDM is now to use 388/tcp and 388/udp and only use RPC (service 300029!) as a fall-back.
It's probably worth considering making it a compile-time or run-time option to disable RPC entirely since most LDM servers don't seem to use it.
-- Peter Laws / N5UWY National Weather Center / Network Operations Center University of Oklahoma Information Technology plaws@xxxxxx ----------------------------------------------------------------------- Feedback? Contact my director, Craig Cochell, craigc@xxxxxx. Thank you!
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