Troubleshooting
Efficient Video Distribution Networks with.Multicast: IGMP Querier and PIM-DM
19
Keep in mind these general rules:
PIM does not route. Routing must be working for it to work.
No more than 3 hops should be used between the transmitter and receiver when multicast is
used. This does not include a Rendezvous Point when using PIM-SM, but only refers to the
shortest path that is taken after pruning.
Rendezvous Points (first and redundant) when using PIM-SM need to be as close to the center of
the network as much as possible.
Multicast Frames Explained
Multicast IP addresses fall in the range of 224.0.0.1 and 239.255.255.255. These multicast addresses
are only used as a destination, never as a source address. The destination addresses given to multicast
traffic is a combination of the number 01:00:5E and the last 23 bits of the multicast IP address
(ignoring the first 9 bits). Since the first octet of the MAC address has a value of 1 (01:xx:xx:xx:xx:xx),
it denotes it as a multicast MAC address and is therefore handled differently in the switch than a
unicast MAC address.
For example, the IP address 239.0.0.1 has a destination address of 01:00:5E:00:00:01, and the
multicast IP address of 239.0.0.2 has a destination address of 01:00:5E:00:00:02. These multicast
destination addresses will be seen in every multicast UDP packet captured in Wireshark.
Bandwidth Considerations
Video Streaming in high quantity or high quality takes considerable network bandwidth. Test and fine-
tune your equipment thoroughly using the User Guide and CLI Reference Guide for your particular
switches. LAGs used on access ports and trunks can also provide additional bandwidth to allow the
network and servers to handle the traffic. When using PIM-SM (not covered in this document), place
the RP in a strategic location that is most beneficial for efficient video distribution. More information
about PIM-SM, including an example, can be found in the User Guide.
Useful Links
Reference Links Table 5.
VLC Media Player
http://www.videolan.org/vlc/download-
windows.html
WireShark
http://www.wireshark.org/download.html
IPv4 Multicast Address Assignments
https://tools.ietf.org/html/rfc5771
Internet Group Management Protocol, Version 3
https://tools.ietf.org/html/rfc3376
Protocol Independent Multicast - Dense Mode
(PIM-DM)
https://tools.ietf.org/html/rfc3973
Protocol Independent Multicast - Sparse Mode
(PIM-SM)
https://tools.ietf.org/html/rfc4601
IPv4 Multicast Address Space Registry
http://www.iana.org/assignments/multicast-
addresses/multicast-addresses.xml
Considerations for Internet Group Management
Protocol (IGMP) and Multicast Listener Discovery
(MLD) Snooping Switches
http://tools.ietf.org/html/rfc4541