Multicast routing on VPN

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Sep 22nd, 2009
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I have a pair of RVS 4000 routers bridging two sites with a VPN and all is fine, save for the fact that most of the resources I need to access through the VPN rely on multicast packets to advertise their availability. Is there any way to tell the routers to route multicast packets across a VPN? As far as I can tell there is not, but I thought I better ask.

If there is no way to route multicast packets over the VPN then my second question is how does one go about getting Cisco to add a feature? Mutlicast is increasingly important to the Small Business market being targeted by these products. NAS devices, printers, scanners and all sort of other devices are using UPnP, mDNS and other multicast protocols to make themselves findable when they are getting their IP addresses using DHCP. Half of Apple's product lines rely on Bonjour, which is mDNS under the hood. The point of a VPN is to allow offices to join together, supposedly seamlessly, but without multicast routing most of my resources are inaccessible half the time.

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Glenn Quesenberry Tue, 09/22/2009 - 15:49
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     IPSec by design does not support multicast traffic, so what you could do is use a GRE tunnel instead.  However, the RVS4000 does not support GRE tunneling since it's a Small Business router.  You would have to move up to a traditional Cisco IOS-enabled router to get that capability.  If you're interested there's a good document here that explains Multicast over VPN:

Best Regards,


nickovs123 Tue, 09/22/2009 - 18:08
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Thanks for the reply. I understand that raw IPSec does not support multicast but it is straightforward to implement a daemon on the router that would pass multicast packets on to the other router(s) in the network over IPSec. Several open source ones already exist.

With respect, saying "the RVS4000 does not support GRE tunneling since it's a Small Business router." sort of misses the point. While once upon a time multicast was an esoteric technology mostly used for video distribution, these days the overwhelming majority of multicast endpoints are using it to solve the service discovery problems faced by people who don't have an entire managed local DNS system. These are precisely the Small Business customers, so this is exactly the sort of thing that is needed on Small Business routers. If your goal is to keep the customer satisfied then, surely, it would be of substantial value to add this sort of functionality to the RVS4000, RV082, WRVS4400 and their kin.



Glenn Quesenberry Wed, 09/23/2009 - 13:21
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     Thanks for the open dialog!  Can't say that I disagree with you, but rather wanted to provide some input into what is available today with the products available.  I will forward this discussion to the Small Business router product team as far as product enhancement and improvement is concerned, and see how prevalent this type of request has been.  We always appreciate and want feedback from our partners and customers and your's is no exception.  I'll escalate this up and will keep you posted on what I find out.

     Thanks again and please keep the dialog and feedback coming!

Best Regards,