Large IPv6 Multicast Domains

David Barak thegameiam at
Fri Jun 27 04:25:04 CEST 2014

> On Jun 26, 2014, at 7:05 PM, Stig Venaas <stig at> wrote:
> Hi
>> On 6/20/2014 5:08 AM, David Barak wrote:
>>>> On Jun 20, 2014, at 5:09 AM, Phil Mayers <p.mayers at> wrote:
>>>>> On 20/06/14 07:11, Mark Tinka wrote:
>>>>> On Thursday, June 19, 2014 08:17:07 PM Stig Venaas wrote:
>>>>> I'm
>>>>> hoping SSM will be the way to go for interdomain in
>>>>> general.
>>>> Agree - prefer SSM also.
>>> Who doesn't - app coders AFAICT? ;o)
>> There are specific use cases for ASM (in IPv4) in distributed monitoring (many->few traffic flows)  It sure would be a shame for that to go away...
> But do you need that across multiple domains?

Define "domain" in that context- do you mean PIM domain, or do you mean administrative control, ASN, MSDP relationship, or what?  The answer to most of these would be "yes", although to varying degrees.

> ASM is pretty much the only solution when it comes to autoconfig
> and discovery where you don't want to hard code source addresses
> and some device has no knowledge. But that is typically relevant
> on a single link, or in a site. I can't think of any interdomain
> cases.

Distributed sensor networks are a specific example of a multi-site use case for ASM.  

> Applications that need to discover remote sources for SSM would
> need to have their own discovery mechanism. There are various
> possible schemes. A device with no info might need to use DHCP
> or something to learn how to reach a server, or maybe have some
> fixed multicast group to discover some kind of local server that
> has more info.
> But yes, it is easier for application developers to assume ASM
> works inter-domain. Embedded-RP works though, but you would
> probably not want to hardcode a group addresses with an embedded
> RP address in a device.
I'm looking at perfectly functioning ASM networks in IPv4, and hoping the functionality doesn't go away or become a lot harder because v6 multicast is over designed.  Right now, an app needs its own source address and the group or groups to send to, *and that's it*.  Am I stuck with embedded-rp if we move to v6?  What if (Heaven forfend) I want to change the rp address, or use BSR or something?

David Barak
Sent from a mobile device, please forgive autocorrection.

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