Both real equipment as well as the GNS3 should have the same debug output. When implementing debugging, make sure that you also employ the terminal monitor command in order to tell the device that all debug output should appear on the terminal screen. Also, verify that IGMP is indeed enabled and that you have achieved the necessary connectivity between the hosts and R1 before implementing the commands on the hosts.
Take a look at these and let us know your results!
Hi Laz, Can you explain it please ?Please correct me if am wrong. 224.0.0.1 addresses all the host on a network segment. This IP is used by the router to send membership query to all host to ask whoever interested in multicast traffic. And then followed by this you say that 239.1.1.1 multicast IP is the actual IP address that is used to send the multicast traffic to the host participating in the group ? I donāt understand here.
Do you mean 239.1.1.1 is the multicast IP address that host uses when they are sending the membership report ?
Please confirm
Yes, this is correct. All IP hosts on a segment will receive such a message. This multicast address only remains within the segment, and is not routable to any other network segments.
This multicast IP address is the multicast group which the hosts in this lesson want to join. This is seen by the following commands issued on the interface of H1 and H2:
Unlike the 224.0.0.1 address, which is a well known and reserved address, the 239.1.1.1 multicast group address is configurable. This means that some hosts choose to join it, while others may choose not to. It is the destination address used by multicast sources to send their content to. A video server, for example, would use this as the destination address to reach all hosts interested in its multicast stream.
Yes, this address is also used by hosts to send their membership reports. The membership reports actually tell the multicast router that the host sending the report wants to receive multicast traffic destined for this particular multicast IP address.
Speaking of enabling multicast routing, in your topology, H1 and H2 are Cisco routers, but in your configuration example, I did not see the command ip multicast-routing on H1/H2. For routers to participate in multicast, do you not have to enable on all routers in global config mode even when they are behaving as hosts??
As you correctly stated, H1 and H2 are actually routers, but are functioning as hosts. Within the framework of multicast, hosts (even if they are Cisco routers) do not perform multicast routing. So to answer your question, no, multicast routing does not (and actually should not) be enabled on routers that play the role of a host.
Think about it this way. If you have a Windows PC connected to the network, and it wants to participate in a multicast group, it can do so even through it does not have the capability of multicast routing itself. For hosts of any type to participate in multicast, they simply have to support IGMP and the functionality of joining of multicast groups.
For IGMPv1 the intervals I think you are talking about are:
Query Interval = 60 seconds
Group Membership Interval = 180 seconds
You can see the default values of all IGMP timers on a particular interface using the following command: show ip igmp interface <interface>. Keep in mind that intervals vary from IGMPv1 and IGMPv2.
Iām still not sure how this multicast traffic reaches the router since the host destination multicast address is 239.1.1.1 but the router uses 224.0.0.1. How does the router know it has received the multicast traffic from the host since I donāt see 239.1.1.1 configured on the router side. Can you please clarify
First of all, multicast traffic does not reach the router. The router is not the destination of multicast traffic. It is the hosts that receive this traffic. The router is configured to send multicast traffic, and when it is sent, it goes to all hosts that have requested it.
When traffic that is destined to 239.1.1.1 is sent from the router, it will go to all hosts that have requested such traffic. If you take a look at the multicast routing table of R1, you will see that group 239.1.1.1 is in the table, and it corresponds with the GigabitEthernet0/1 interface.
Now I believe that your question was, how does the hostās membership query reach the multicast router using a destination address of 224.0.0.1 since this address is nowhere to be seen in the router itself, correct? Well, this is a special reserved multicast IP address called an āall hosts multicast group addressā. By default, all multicast hosts on a network segment belong to this group. So even though you canāt see it anywhere, multicast hosts and routers are always a part of this group. So any packet sent with a destination of 224.0.0.1 will reach all multicast-enabled devices, including the router.
Hello Rene, but iām a little bit confused because in the video you explain and demostrate when there no more hosts listening to a multicast group ip address, the multicast router remove this ip multicast address of the multicast routing table.
IGMP version 1 does not have a message that can explicitly and proactively allow a host to inform a router that it doesnāt want to receive traffic anymore. However, IGMP version 1 does have a timer mechanism that allows a router to determine if there are still interested multicast hosts or not.
As stated in the lesson:
The router will periodically send a membership query to destination 224.0.0.1 (all hosts multicast group address). Hosts that receive this message will respond with a membership report to tell the router that they are still interested in receiving the multicast traffic. When the router receives the membership report, its expiry timer will be refreshed. When no hosts respond, the router knows that nobody is interested anymore in the multicast traffic and it will then remove the entry once the timer exceeds.
So if the timer times out and no host sends any membership reports, then the router knows that no one is interested in the multicast traffic. Only then will it remove the entry from the routing table.
