Configuring IGMP in a LAN to control IPTV multicast flows over Cisco Catalyst 3550-12T
In this article a scheme with one device Cisco Catalyst 3550-12T 1 that combines the functions of both a switch and an IGMP querier is described. Catalyst 3550-12T switch has 10 Gigabit Ethernet ports and two ports for GBIC modules. Peak performance is 17 billion
packets per second that allows transmitting data at a 24 Gbps rate.
Configuring IGMP snooping and IGMP querier
It is required to have an IP address configured on the Vlan 1 interface of the switch:
IGMP snooping is enabled by using the command (in global configuration mode):
IGMP querier is enabled by using the command (in global configuration mode):
A stand on basis of Cisco Catalyst 3550-12T ( C3550-IPSERVICESK9-M, Version 12.2(40)SE ) and
NetUP DVB to IP gateway 2 was prepared by NetUP specialists. A general network scheme is
given in the figure 1 below. As the client equipment it was used a PC with vlc mediaplayer and
an IP set-top box AmiNET 130.
Fig. 1. General layout of the test stand.
IGMP snooping and IGMP querier were enabled as discussed above. To check this, one can
use the following commands (the output is provided):
As it can be seen the switch operates as an IGMP querier. In the groups list there are
no groups as no subscriber has requested a multicast stream. In this case the average
data transfer rate on the client’s port equals 0 Mbps. To check this run the following
At that on the port of NetUP DVB to IP gateway we can see data transfered
at the rate of 110-120 Mbps (full decoding of 4 transponders is performed
that is around 50 TV channels):
Due to IGMP snooping multicast packets are not coming to the client port. If the client
requests a TV channel, copied to his port are only those multicast packets that belong
to this TV channel. To check this let’s request a TV program on the client’s device:
The requested TV channel appears on the client’s TV screen. And on the switch in the groups list we can see a new record:
As we can see from this record, the switch is copying multicast packets for the group 18.104.22.168 to
the client port (Gi0/2). To check this we can check the rate of data transfer to the client port:
As it can be seen, only one TV channel is being transfered to the client port at the rate of ~3 Mbps. Because of such behavior of the switch we avoid overloading the client’s port with unwanted multicast packets.
It is worth of noting that the CPU load of the switch is almost zero. Most likely
multicast packets are processed at the hardware level.
Important! According to “IPv4 Multicast Unusable Group And Source Addresses” 3 it is not recommended
to use certain ranges for IPv4 multicast addresses. For example, subnet 22.214.171.124 – 126.96.36.199. Cisco
Catalyst 3550-12T switch sends multicast packets to all ports regardless of client’s requests.
- Cisco Catalyst 3550-12T switch description – http://www.cisco.com/en/US/products/hw/switches/ps646/ps645/index.html
- NetUP DVB to IP gateway overview – http://www.netup.tv/en-EN/decoder-streamer.php
- IPv4 Multicast Unusable Group And Source Addresses – http://tools.ietf.org/html/draft-ietf-mboned-ipv4-mcast-unusable-01