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