Multicast – Troubleshooting Multicast Issues in a Two-Segment Network

multicastpimrouting

I have two network segments connected to a single Cisco router by Cisco switches. I've enabled multicast routing on the router by running following commands:

  1. ip multicast-routing in configuration mode
  2. ip pim dense-mode on each interface

And set following route on the hosts for multicast traffic:

  1. route add -net 224.0.0.0 netmask 240.0.0.0 dev eth2

According to my searches the multicast traffic should cross the networks without setting route for their network (128.238.61.0 and 128.238.62.0 here), but is not the case. I tried following solutions, but neither worked:

  1. Using sparse-mode and dense-sparse-mode for interfaces
  2. Enabling and disabling Reverse path filtering from /proc/sys/net/ipv4/conf/[all,defalut,eth2]/rp_filter by writing 0 and 2 in it.

I use netspy to create multicast traffic and groups (224.111.111.111) and I've verified that the corresponding address is in the multicast groups of router interfaces. Also hosts inside a single network segment can see the multicast traffic properly. As I think the traffic should cross the networks without setting route, what misconfigurations may cause this problem. Thank you in advance.

There is one router with interface IPs: 128.238.61.1/24 and 128.238.62.1/24. To each port of the router a switch is connected. To each switch three hosts are connected. I connect to router by telnet and then type config term. Then I type ip multicast-routing. I go to interfaces with command int fa 0/0 (0/1) and type ip pim dense-mode. Then on the host with ip 128.238.61.109/24 I start netspy by typing netspyd 224.111.111.111 1500 6 (parameters are group ip, port and ttl). Now on all other hosts I type netspy 224.111.111.111 1500. Now if I telnet from one of the hosts on the same side as the netspyd to it (109) nothing happens. If I set on all hosts route route add -net 224.0.0.0 netmask 240.0.0.0 dev eth2 and then do the telnet hosts on the same side of as the netspyd server (network 61.0) get the message about the log on but others don't.

Best,

Best Answer

PIM is a router-to-router protocol. I think what you are missing is IGMP. The clients wanting to receive traffic from a multicast groups will use IGMP to inform the router that they wish to receive the traffic:

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Based on your configuration commands, I assume you are using a Cisco router. Cisco has a document which describes all of this and how to configure multicast routing.

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