Tuesday, October 7, 2008


I got a mail form one of my friend saying given words

Thanks a ton for the detail. Well, I was sure of using that to make a comfortable network management while configuring the multicasting. Just since heard that link can be established without using that so as did ask to you.

Like we had a word about the MDT value in the same evening, I believe we are not using it in every configuration and like you told me that it is making a tunnel. Requesting you please explain me little bit in detail. Because my query is, If we are using 2 end to end interfaces which will be delicately responsible for the Multicasting through an IGMP group and a Rendezvous IP address then how & when MDT value comes into play in terms of comfortablity.

Shivlu Says:-

Regarding IGMP Probelm:-
Actually you can use the multicasting without IGMP but the problem is that when you donot use the IGMP PC or receiver by default takes the TTL value that is 128 or 64. As you know multicast traffic is CPU oriented. Without using IGMP the last hop router also not able to know which group he has to join becasue no one is going to send the request to router. In that case it has to manage all the entries in router. But when you use IGMP it sets the TTL=1 it means you laptop is going to send a request to its nearest gateway with TTL=1 and packet is not propagated in the network. So that router will look forward for that group which you laptop is requesting and create a (s,g) entries. In this way routers has fully control of join & leave request.

Regarding MDT Problem:-
Actually what happens MPLS doesn't supoprt multicast but rosen (name of the guy who proposed the solution) proposed a draft in which he mentioned that we can use the multicast with the help of multicast tunnel. For that every VPN should have default MDT group which is mandatory and MDT data is optional. So when you configure MDT default in one vrf and same mdt default in the another end of same VRF it creates multicast tunnel. You can check my previos post of MVPN which explains all the things (http://shivlu.blogspot.com/2008/09/case-study-mvpn-part-1.html)I am talking about. So after tunnel creation all the multicast floods on tunnel.

Hope I replied as you are looking for.

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