This guide has been created to help you when you receive a cisco multicast troubleshooting error.

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    The most common problem in a multicast network 2 . 0 means that the packets transmitted by the learning resource do not reach the recipients. Other problems can be related to shaping, most often associated with the distribution tree itself and unnecessary flooding in switch LAN environments.


    This document discusses A common dilemma that occurs when you publish a multicast application on a Cisco Catalyst Web Switch for the first few days and multicast does not work. Also, if families do not configure switches efficiently, some servers/applications that use multicast packets for clustering/high availability features may not work. The document also discusses this vision.



    Components Used

    The information in this document is generally based on the following hardware and software versions:

  • Catalyst 6500 with Supervisor Engine 720, which experts say is running Cisco IOS® Software Release 12.2(18)SXD5

  • Catalyst 3750 running Cisco IOS Image Release 12.2(25)SEB2

  • How do you check multicast packets?

    Use the show internet protocol igmp groups command to verify this. If you don’t have real recipients, copy them to the ip igmp join routers with this command. Then send an mtrace request to the RP’s address between each end router to which the target is connected. Use the mtrace [rp ip address] command to handle this.

    The information in this report was collected from devices in a specific lab environment. Everything about the devices used in this warranty plan started with a remote (default) configuration. If yourto be active, make sure you understand the upcoming implications of each command.

    Related Products

    This document can also be used with the following garden and software versions:

  • Any Catalyst switch running your own version of Cisco IOS software with Internet Group Management Protocol (IGMP) snooping.

    Catalyst multicast switch support matrix per letter, around these switches only for their identification.

  • Agreements

    See Cisco Technical Tips for more information on conventions.


    It appears that multicast traffic cannot pass through Catalyst switches, even on the same VLAN. On fig. 1 shows a typical scenario:

    Rice. 1. Network configuration in addition to multicast source and destinations

    The multicast boot connects to switch 1, which is sometimes a Catalyst 6500 switch with a modulolem Supervisor Engine 720 running Cisco IOS software. Receiver 1 is fully connected to switch 1, and multiple receivers are connected to switch 2. The switch is a pair of Catalyst 3750s. There is a layer link between switch i and switch 2, often access or connection.

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  • In this configuration, find out where sink 1, which is on the same switch as the source, can receive a multicast stream with certain issues. However, receiver 2 does not receive any multicast traffic. This document attempts to solve this problem.

    Revisit Some Important Multicast Concepts

    How do I know if multicast is working?

    To verify that multicast is working properly on your main network, you can use the following quick tcpdump/ping test. If multicast is working correctly, you are indeed seeing packets arriving at the source node. Repeat this process on the Together node to ensure multicast is also correct on your network.


    Your organization should be familiar with some of the key concepts of Layer 2 multicast before exploring the solution and then exploring the various options available to you. This section defines the concepts.

    Note. This section gives a correct, very simple and clear explanation, and focuses only on this particular issue. A more detailed explanation of these termssee the Information section of this document.


    IGMP is a method that allows end hosts (recipients) to notify a multicast router (IGMP query) that an end host intends to receive certain multicast traffic. So this approach is a protocol that works between the router and end hosts, or allows:

  • Routers that allow end nodes to be asked if they want a particular multicast flow (IGMP request)

  • cisco multicast troubleshooting

    End nodes report or reply to the router when looking for a specific multicast stream (IGMP reporting)

  • IGMP Snooping

    IGMP stealth is a mechanism to restrict multicast traffic to only those ports that experts believe are connected to recipients. This mechanism improves efficiency because it allows the layer 2 switch to selectively send external multicast packets to only those ports that definitely need them. Without IGMP penetration, packets are forwarded on every port. TOthe switch “listens” for IGMP messaging according to the router and stores the end. Thus, the switch creates an IGMP snooping table containing a list of all sockets that have requested the selected multicast group.

    Router Port

    The Mrouter port is simply the port from which the switch is not visible when connected to a multicast router. Having a real mRouter port is required for the IGMP snooping operation if you want to work on production switches. This document describes the problem and its solutions in more detail.

    cisco multicast troubleshooting

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