Sunday, July 8, 2007

IP multicasting

IP multicasting is a very interesting thing .... many protocalls to handle the Multicast traffic at different segments of the network ...but all the traffic is sent as UDP ( RTP ) ..

typical IP ulticasting environemnt with IGMP and PIM protocalls will look like this ,



PIM - is used by Router to communicate with eachother about which multicast traffic to forward and which not to.

IGMP - For Video clients to join to their local multicast server to watch videos


in my environment I already simulated the IGMP part , for that I used following equipment :

Local Multicast router : L3 DLINK swithc / PANEX SF-0420G - both are swicthes with Multicast routing feature for IGMP

L2 switch for IGMP snooping : BAS-8124 Hitron DSLAM / DLINK DES-3516/ Dray Tek A24M DSLAM

Multicast server / Multicast client : http://www.videolan.org/ - VLC media player

VLC media player is one cool software , easy to configure and works perfectly ...

VLC player - server configuration :








File - Open ->





Streaming setting - select RTP and set the Multicast address :

Multticast address range is :
IP : 224.0.0.0 through 239.255.255.255

these IP addresses are mapped to MAC address of the form : 01:00:5E :xx:xx:xx

to lean about multicast address range and MAC to IP mapping of Multciast addresses : http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/ipmulti.htm#wp1020554

*** some multicast addreses are used for special purposes therefore ,to be in the safe side , I notmally use :

225.1.1.5, 226.1.1.6, 227.1.1.7


now if u want to see wheter ur Video server is working ..... its very simple , just connect another PC with the VLC media player to the same hub ( do not use a switch for this simple test cos IGMP snooping fatures in the switch will bloc the multicast traffic )
Video client settings : just enter the same multicast address ...
File -> Open Network Stream (ctrl+N)


...yha you can watch the video stream you are sending from the Server now !!! ..pretty easy ha ..
to set up the IGMP environment :

Local Multicast router - configure the quarry interval

L2 switch - enable IGMP snooping


*** procedure depend on the particular device but the setting names are common ,it should not be difficult to configure .


*** when u join a video stream you can watch video but after some time like 5minutes the video time out - this happens when the Multicast router is not sending Periodic membership query , check ur local multicast router configuration .

Testing PIM - I am working on this now , the device I am trying to test only support PIM-DM , and its WAN interface is a Cable modem - therefore I observed the PIM table of CMTS and the Device :
CMTS : Cable modem termination system


CMTS is a router , it can send PIM hello message to it neighbours - The device I am testing (Cable modem Residential gateway ) also send PIM hello to its neighbours - therefore I could observe that CMTS and the Residential gateway can learn that they are neighbours, but so far I was not able to make the CMTS flood multicast traffic to the Cable modem RG ( according to PIM-DM) , I can see the (Source, Group) entry in the CMTS but it does not forward the multicast traffic to the cable interface.
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