Multicast Address

[vishalpatil86]

Hi,

What is multicasting concept and how can I assigh a mulyicast address  to a device??

[John Blakley · Accepted solution]

Multicasting is where a device will send traffic to a multicast address and then hosts that want that traffic will join the multicast group (same address) that the source is sending traffic to. You don't assign a multicast address to a host, but rather whatever software that you're using will send to a multicast address. Suppose that you have a video stream that you want to send to 2 computers. The source PC, addressed at 192.168.1.50, will start its video stream and send to 239.50.50.50. Then you go to the 2 computers and start their application that allows them to watch this video stream. The group address that you join would be 239.50.50.50. During periodic refreshes, the 2 PCs will continually stay joined to the group to receive the stream, but again the 239.50.50.50 isn't physically assigned to any host; it's just where the application will send the traffic.

HTH,

John

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[vishalpatil86]

hi blakley,

Thank you for your reply...

Can you explain the same concept from OSPF(which sends multicast on 224.0.0.5) and EIGRP (224.0.0.10)point of view? it will be more helpful

[John Blakley · Accepted solution]

EIGRP sends on 224.0.0.10 and devices that run EIGRP will automatically listen for those addresses.OSPF sends to all ospf routers on 224.0.0.5 and to DRs on 224.0.0.6 and the OSPF process listens on those groups.

Below is EIGRP debug hello and debug ip packet:

*Mar  1 00:38:31.647: IP: s=192.168.9.3 (local), d=224.0.0.10 (FastEthernet0/1), len 60, sending broad/multicast

*Mar  1 00:38:31.647: EIGRP: Sending HELLO on FastEthernet0/1

The other router doesn't have EIGRP enabled yet, so it doesn't answer on 224.0.0.10:

R4(config-router)#network

*Mar  1 00:39:35.503: IP: s=192.168.9.3 (FastEthernet0/1), d=224.0.0.2, len 48, rcvd 0

R4(config-router)#network

*Mar  1 00:39:36.899: IP: s=192.168.9.4 (local), d=224.0.0.2 (FastEthernet0/1), len 48, sending broad/multicast

R4(config-router)#network

*Mar  1 00:39:38.503: IP: s=192.168.9.3 (FastEthernet0/1), d=224.0.0.2, len 48, rcvd 0

R4(config-router)#network

Below is after enabling R4 with EIGRP:

R4(config-router)#network 192.168.9.0

R4(config-router)#

*Mar  1 00:40:11.479: IP: s=192.168.9.3 (FastEthernet0/1), d=224.0.0.2, len 48, rcvd 0

*Mar  1 00:40:11.831: IP: s=192.168.9.4 (local), d=224.0.0.10 (FastEthernet0/1), len 60, sending broad/multicast

*Mar  1 00:40:11.831: EIGRP: Sending HELLO on FastEthernet0/1

*Mar  1 00:40:11.835:   AS 100, Flags 0x0, Seq 0/0 idbQ 0/0 iidbQ un/rely 0/0

*Mar  1 00:40:11.895: IP: s=192.168.9.3 (FastEthernet0/1), d=224.0.0.10, len 60, rcvd 2

*Mar  1 00:40:11.899: IP: s=192.168.9.3 (FastEthernet0/1), d=224.0.0.10, len 77, rcvd 2

*Mar  1 00:40:11.899: IP: s=192.168.9.3 (FastEthernet0/1), d=224.0.0.10, len 40, rcvd 2

*Mar  1 00:40:11.903: EIGRP: Received HELLO on FastEthernet0/1 nbr 192.168.9.3

*Mar  1 00:40:11.903:   AS 100, Flags 0x0, Seq 0/0 idbQ 0/0

*Mar  1 00:40:11.907: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 192.168.9.3 (FastEthernet0/1) is up: new adjacency

So the routing process is responsible for listening to those groups, but you don't need to have multicast explicitly configured on the router for them to work.

HTH,

John

[vishalpatil86]

naadkhula(awesome!!!!)

thanks a ton john