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233 lines
12 KiB
233 lines
12 KiB
4 years ago
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<!doctype html public "-//w3c//dtd html 4.0 transitional//en">
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<html>
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
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<meta name="GENERATOR" content="Mozilla/4.77C-CCK-MCD Caldera Systems OpenLinux [en] (X11; U; Linux 2.4.2 i686) [Netscape]">
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<title>OpenSLP FAQ</title>
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</head>
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<body text="#000000" bgcolor="#FFFFFF" link="#0000EF" vlink="#51188E" alink="#FF0000">
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<h2>
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OpenSLP - Frequently Asked Questions</h2>
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<hr WIDTH="100%">
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<p><tt>A really compresensive FAQ is not yet available for OpenSLP so please
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send</tt>
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<br><tt>your questions to the OpenSLP mailing lists:</tt>
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<p><tt> openslp-devel@lists.sourceforge.net</tt>
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<br><tt> openslp-users@lists.sourceforge.net</tt>
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<p><tt><b>Q:</b> Where is the configure script to build OpenSLP?</tt>
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<br><tt><b>A:</b> Did you read section 3 of the README? You need
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to run autogen.sh to</tt>
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<br><tt> generate the configure script.</tt>
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<p><tt><b>Q:</b> How do I build OpenSLP on Windows?</tt>
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<br><tt><b>A:</b> The MSVC project files used by the developers who ported
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OpenSLP to win32</tt>
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<br><tt> available in the source directories. If you
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do not use MSVC and you are a</tt>
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<br><tt> Windows developer, then you will be used to trying
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to get MSVC makes to</tt>
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<br><tt> work with your tools</tt>
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<p><tt><b>Q:</b> Will OpenSLP work on my operating system</tt>
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<br><tt><b>A:</b> Yes, the OpenSLP code has proven to be very portable.
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It currently works</tt>
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<br><tt> many operating systems including: Linux, BSD, Solaris,
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Tru64, HPUX, UnixWare,</tt>
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<br><tt> OSR5, and Win32</tt>
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<p><tt><b>Q:</b> I am having trouble discovering attributes using FindAttr()
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and "slptool</tt>
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<br><tt> findattrs". The functions seem to execute properly,
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and the services URL's</tt>
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<br><tt> can be discovered, but no attributes are returned.
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I am registering</tt>
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<br><tt> services in slp.reg files. I don't think it is my
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syntax in the slp.reg</tt>
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<br><tt> file, because the example registrations in that file
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do not return</tt>
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<br><tt> attributes either. Can anyone help?</tt>
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<br><tt><b>A:</b> If you just want to use slptool to see if things are
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working, you need to</tt>
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<br><tt> do the following:</tt>
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<p><tt> Contents of the slp.reg:</tt>
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<br><tt> ------------------------</tt>
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<br><tt> service:myservice1.x://myhost.caldera.com,en,65535</tt>
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<br><tt> owner=Matt Peterson</tt>
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<br><tt> email=mpeterson@caldera.com</tt>
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<p><tt> service:myservice1.x://yourhost.yourdomain.com,en,65535</tt>
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<br><tt> owner=Kim Jackson</tt>
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<br><tt> email=bjackson@yourhost.yourdomain.com</tt>
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<br>
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<p><tt> IMPORTANT: Restart slpd and check the /var/log/slpd.log
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to ensure that</tt>
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<br><tt> there were no errors during parsing of the .reg file</tt>
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<p><tt> Use slptool to find attributes</tt>
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<br><tt> ------------------------------</tt>
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<br><tt> $ slptool findsrvs service:myservice1.x</tt>
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<br><tt> service:myservice1.x://myhost.caldera.com.com,65535</tt>
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<br><tt> service:myservice1.x://yourhost.yourdomain.com,65535</tt>
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<p><tt> $ slptool findattrs service:myservice1.x://myhost.mydomain.com</tt>
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<br><tt> (owner=Matt Peterson),(email=mpeterson@caldera.com)</tt>
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<p><tt> $ slptool findattrs service:myservice1.x://yourhost.caldera.com</tt>
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<br><tt> (owner=Kim Jackson),(email=bjackson@yourhost.yourdomain.com)</tt>
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<p><tt> Note that you need to supply the service-url as returned
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by findsrvs</tt>
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<p><tt><b>Q:</b> I have a multi-homed machine and OpenSLP is not working.</tt>
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<br><tt><b>A:</b> Please read the updated installation guide</tt>
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<br><tt> <a href="http://www.openslp.org/doc/html/UsersGuide/Installation.html">http://www.openslp.org/doc/html/UsersGuide/Installation.html.</a></tt>
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<br><tt> There are special instructions for users of multi-homed
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machines.</tt><tt></tt>
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<p><tt><b>Q:</b> In our development lab, the multicast SLP requests work
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just fine.</tt>
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<br><tt> However, in our SVT lab, the multicasts requests never
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work. We always</tt>
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<br><tt> have to edit the slp.conf file and turn on broadcast.
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Have any others seen</tt>
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<br><tt> this? Do you recall what the solution was?
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We have spent a great deal of</tt>
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<br><tt> time trying to figure this one out without success.</tt>
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<br><tt><b>A: </b>Yes, others have seen this behavior -- I know I have.
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I should put this in</tt>
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<br><tt> the FAQ because I get a lot of questions. The
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following is a list of the</tt>
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<br><tt> most common problems along with trouble shooting and
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resolution info:</tt><tt></tt>
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<p><tt> No multicast route</tt>
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<br><tt> -------------------</tt>
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<br><tt> A very common problem with some OS installations (especially
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Linux) is</tt>
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<br><tt> that there is no multicast or default route set up.
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On systems with BSD</tt>
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<br><tt> derived TCP/IP stacks (nearly all OSes), broadcast
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and multicast traffic</tt>
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<br><tt> are delivered using the unicast routing table.
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If the unicast routing</tt>
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<br><tt> table does not have either a default route or an explicit
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multicast route,</tt>
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<br><tt> then the kernel does not know where to send the SLP
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datagram and returns</tt>
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<br><tt> an error 101 - network unreachable error which translates
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into a SLPError</tt>
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<br><tt> -23 SLP_NETWORK_ERROR. A quick test is to try to ping
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SLP multicast:</tt><tt></tt>
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<p><tt> $ ping 239.255.255.253</tt><tt></tt>
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<p><tt> If ping returns an error that the network was unreachable,
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you will need</tt>
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<br><tt> to set up a default route or a multicast route.</tt>
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<br><tt> </tt>
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<br><tt> Note you may not get any responses to the ping.
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This may not indicate</tt>
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<br><tt> a problem. The only thing to be concerned about
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is if there is an error</tt>
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<br><tt> actually sending the ping.</tt>
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<br><tt> </tt>
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<br><tt> Please read the installation instructions for more
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information on how</tt>
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<br><tt> to install a multicast route:</tt><tt></tt>
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<p><tt> http://www.openslp.org/doc/html/UsersGuide/Installation.html</tt><tt></tt>
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<p><tt> </tt>
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<br><tt> The "smart switch /stupid router" problem</tt>
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<br><tt> ------------------------------------------</tt>
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<br><tt> The smart switch / stupid router (or no router) problem
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is something that</tt>
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<br><tt> happens on switched ethernet networks only.
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If you do not have a</tt>
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<br><tt> switched ethernet network, then you do not have this
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problem. If you do</tt>
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<br><tt> have a switched ethernet network, then you may have
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this problem if you</tt>
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<br><tt> are using newer switching hardware. The reason
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is that ethernet</tt>
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<br><tt> switching hardware is smart enough to monitor IGMP
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traffic and only</tt>
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<br><tt> forward multicast ethernet frames to those ports that
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are connected to a</tt>
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<br><tt> host that has maintained the appropriate IGMP conversations
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with the</tt>
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<br><tt> router.</tt><tt></tt>
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<p><tt> At a very high level, IGMP works like this. First,
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the host joins the</tt>
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<br><tt> multicast group by sending the router an IGMP message.
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The router</tt>
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<br><tt> responds periodically with request to the host to
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see if the host is</tt>
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<br><tt> still interested in multicast traffic. Since
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IGMP conversations are</tt>
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<br><tt> handled transparently by the kernel level IP stack
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implementations, most</tt>
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<br><tt> developers and users do not even realize anything
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is happening.</tt><tt></tt>
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<p><tt> However, "smart" ethernet switches do realize something
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is happening!</tt>
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<br><tt> If they do not see the IGMP messages being sent from
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the router to a host</tt>
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<br><tt> that is plugged into a given port of the switch, then
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they will will not</tt>
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<br><tt> forward multicast ethernet frames to that port.
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This is good and bad.</tt>
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<br><tt> It is good because it makes multicast extremely efficient
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in terms of</tt>
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<br><tt> physical network usage. However, it also makes
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it so multicast will not</tt>
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<br><tt> work at all if a router does not exist (or does not
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support IGMP) to</tt>
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<br><tt> maintain it's end of the IGMP conversation.</tt><tt></tt>
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<p><tt> Trouble Shooting:</tt><tt></tt>
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<p><tt> Monitor IGMP traffic! Make sure that periodic
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IGMP traffic is happening</tt>
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<br><tt> on your network. IGMP traffic can be monitored
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on Linux (and many other</tt>
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<br><tt> OSes) with the following command:</tt>
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<br><tt> </tt>
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<br><tt> # tcpdump igmp</tt><tt></tt>
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<p><tt> Issue this command before starting slpd. You
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will notice that several</tt>
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<br><tt> IGMP "report" messages are sent. The important
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thing to look for a IGMP</tt>
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<br><tt> "query" message from the router. If you do not
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see the IGMP query</tt>
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<br><tt> message from the router then you will soon find that
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you will no longer</tt>
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<br><tt> see any "report" messages either.</tt><tt></tt>
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<p><tt> Another good test is to try to ping the multicast address
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and see where</tt>
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<br><tt> it is visable.</tt>
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<br><tt> </tt>
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<br><tt> $ ping 239.255.255.253</tt><tt></tt>
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<p><tt> Finally, the best advice is to read the normally untouched
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section of</tt>
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<br><tt> your ethernet switch manual that describes how the
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switch handles</tt>
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<br><tt> multicast. Stupid/inexpensive switches treat
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multicast frames exactly</tt>
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<br><tt> like broadcast frames which means that they are forwarded
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to every port</tt>
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<br><tt> of the switch. Smart/Expensive switches often
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allow this behavior to be</tt>
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<br><tt> configured. If you are on a network without
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a router, then it is</tt>
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<br><tt> possible that you might need to "dumb down" your switch.</tt><tt></tt>
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<p><tt> Broken NIC driver</tt>
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<br><tt> ------------------</tt>
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<br><tt> Some NICs do not support multicast operation, so the
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driver does the</tt>
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<br><tt> work by placing the NIC into permiscuous mode
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(accept everything) then</tt>
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<br><tt> the driver filters out what is not needed. The
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problem with this is</tt>
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<br><tt> that sometimes on a very busy ethernet, the NIC buffers
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may not be able</tt>
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<br><tt> to keep up with all the traffic and some frames will
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be dropped. This</tt>
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<br><tt> is normally not a problem since SLP is designed to
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work on unreliable</tt>
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<br><tt> physical networks, but if enough frames are dropped,
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OpenSLP may not</tt>
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<br><tt> be able to find DAs or other services. This
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would result in erratic</tt>
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<br><tt> behavior.</tt>
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<br><tt></tt>
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<br><tt></tt>
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<br>
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</body>
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</html>
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