Table of Contents
What is the multicast problem?
The most common issue in a multicast network is packets transmitted by the source not reaching receivers. Other issues could be related to the formation of the distribution tree itself, and unwanted flooding in LAN environments that use switches.
How multicast is working?
Using multicast, a source can send a single copy of data to a single multicast address, which is then distributed to an entire group of recipients. A multicast group identifies a set of recipients that are interested in a particular data stream, and is represented by an IP address from a well-defined range.
What port does multicast use?
On a typical home network there are a variety of protocols that use multicast. The SSDP (Simple Service Discovery Protocol) uses multicast address 239.255. 255.250 on UDP port 1900.
What is the default multicast port number?
The default multicast address that is used is 239.255. 166.17. This address is configurable, with a port range of 10 ports, starting with the multicast base port for the instance.
Should I enable multicast routing?
The benefit of higher multicast rate is to lower the amount of wireless collisions that your wifi data may have. The biggest effect is seen only when you run multiple media streaming devices or services at the same time. First off, the best setting for multicast rate for your router is usually the lowest amount.
How do I set up multicast?
Enabling multicast on an IP address
- To check if multicast is enabled already on an IP address use the “ifconfig” command. # ifconfig eth0 | grep -i multi UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1.
- To disable multicast on a spcific ip/interface:
- To enable multicast on a specific ip/interface :
Does port matter in multicast?
@Ryan, a port number is an address of a layer-4 protocol, and it really has nothing to do with a multicast (IP, layer-3) address. If the layer-4 protocol you use for multicast is UDP (common), then UDP requires a port number. UDP has no idea if you are using unicast, broadcast, or multicast.
Does multicast require a router?
In networks where there is no router present to act as a multicast router, a switch with IGMP snooping querier enabled can be used to generate the needed IGMP messages to get users to subscribe to multicast traffic.
Which routers are properly configured for multicast?
This network diagram is used as an example. In the figure, Routers 75a and 75b and the Catalyst 5000 (Switch A) are properly configured for multicast and Cisco Group Management Protocol (CGMP). The host gets the multicast traffic.
What happens when multicast packets hit the switch?
Multicast packets, that come from the source, do not trigger the router to send CGMP self-joins to the switch. Therefore the packets hit the switch and get flooded everywhere within the VLAN. This scenario continues until a host in the VLAN, that comes off a port on the switch, sends an IGMP join.
How does IP multicast handle multiple equal cost paths?
When faced with multiple equal cost paths to a source, IP multicast chooses the interface that has a Protocol Independent Multicast (PIM) neighbor with the highest IP address as the incoming interface and then sends prunes to PIM neighbors on the other links.
What causes unwanted flooding of multicast packets on a subnet?
This section explains how unwanted flooding of multicast packets can occur when Cisco Group Management Protocol (CGMP) is not enabled on all routers on a particular subnet, and how this problem can be avoided. This network diagram is used as an example.