Multiple GRE for multicast over ADSL

Unanswered Question
Feb 19th, 2008

Hi. I'm working with a proprietary application that makes UDP Multicast trasmission in a group of 10 endpoint; I was wondering about setting up such multicast group over ADSL using 1800 routers and GRE. But with Cisco GRE can I build multiple tunnels in such way that let each endpoint to reach each others transparently?

Thanks

E.Richiardone

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Paolo Bevilacqua Tue, 02/19/2008 - 09:09

Hi, we do use multipoint gre tunnels to send multicast to less that one hundred sites, it works well.

I would be cautios if going up to 1,800 with anything less than a top platform, but either you use point-to-point, or multi-point GRE, at some point it merely becomes a memory copy operation, also consider that the 1,800 copies of the packet will need to go out anyway on the same wire, so make your bandwidth calculations.

emmanuelrr Tue, 02/19/2008 - 09:21

Thanks for the instant reply.

Sorry I was speaking of 1800 series routers, the endpoints are eleven or twelve, so I don't think to have too much problem of memory allocation or bandwith.

So what I need is multipoint GRE in each node; but what is the overhead introduced by the GRE encapsulation?


Richard Burts Tue, 02/19/2008 - 09:24

Paolo


While it is a bit ambiguous I believe that emmanuel was talking about 1800 as a model identifier and not as the number of routers (especailly since his post does talk about 10 endpoints).


I agree with you that sending multicast over GRE tunnels does work well.


[edit] after making my post I saw the response from emmanuel which confirms that 1800 was a model designation and not a number of router end points.


The amount of overhead introduced by GRE is 24 bytes added to the packet that is to be transmitted over the GRE tunnel.


HTH


Rick

Paolo Bevilacqua Tue, 02/19/2008 - 09:43

Ahah! Taking "1800 routers" for number of and not type! Time for me to go home!


Seriously now, we've a 1841 with the AIM VPN module, does perfectly for moderate bandwidth, but a lot of multicast. We will be upgrading it soon anyway.


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