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README-debug.md

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$Id: README.debug,v 1.4 2002/11/17 20:01:31 pavlin Exp $

This file contains some hints how to debug your multicast routing.

NOTE: currently, it is very incomplete. If something is missing and/or unclear, email to the current maintainer of pimd or file an issue in the GitHub issue tracker.

  1. Make sure that the TTL of the sender is large enough to reach the receiver. E.g., if the sender and the receiver are separated by a two routers in the middle, the TTL of the data packets transmitted by the sender must be at least 3.

  2. Make sure the receiver sends IGMP join (membership report) for the group(s) it wants to receive. Use tcpdump on the router closest to the receiver to make sure. Sometimes buggy IGMP snooping switches, or cloud provider networks, filter out multicast in general, or all control traffic (IGMP/PIM) in particular.

  3. Before you start the multicast routing daemon, verify the kernel config, the following settings should be activated:

    • On Linux:

             CONFIG_IP_MROUTE=y
       CONFIG_IP_PIMSM_V1=y
       CONFIG_IP_PIMSM_V2=y
       CONFIG_IP_MROUTE_MULTIPLE_TABLES=y    # Optional

      Check the list of multicast capable interfaces:

             cat /proc/net/dev_mcast

    • On *BSD:

             options    MROUTING         # Multicast routing
       options    PIM              # Enable for pimd

    • Start the multicast routing daemon in debug mode. E.g., pimd -dall or if you just want to see some subystems: pimd -drpf,mrt -s7

  4. After you start the multicast routing daemon

    • Are the multicast vifs correctly installed in the kernel:

      • On Linux:

             cat /proc/net/ip_mr_vif

      • On *BSD:

             netstat -gn

  • Is multicast forwarding enabled on those vifs:

    • On Linux:

           sysctl net.ipv4.conf.eth0.mc_forwarding

      For each of the enabled interfaces. If it returns zero, the multicast forwarding on that interface is not working.

    • On *BSD:

           sysctl net.inet.ip.forwarding
     sysctl net.inet.ip.mforwarding      # Only OpenBSD

  • Is the PIM multicast routing daemon exchanging PIM_HELLO messages with its neighbors? Look into the debug messages output; if necessary, use tcpdump as well.

  • Are the Bootpstrap messages received by all PIM-SM daemons?

  • If a Bootstrap message is received, is it accepted, or is it rejected because of a wrong iif?

  • After a while, does the Cand-RP set contain the set of RPs?

  • After the first multicast packets are received, is there CACHE_MISS signal from the kernel to the user-level daemon?

  • After the CACHE_MISS signal, are the MFC (Multicast Forwarding Cache) entries installed in the kernel?

    • On Linux:

           cat /proc/net/ip_mr_cache

    • On *BSD:

           netstat -gn