Glen Kent glen.kent at gmail.com
Wed Dec 28 23:58:53 UTC 2011

SSM is also used since we *know* the IP addresses of the content
servers that are the sources - You dont need ASM. I dont think
maintaining RP infrastructure is trivial. Who wants to deal with
register packets, etc. Small routers punt all registers to CPU and
them forward them in SW.

In fact there was a draft which proposed using MPLS encapsulation in
networks that support MPLS to replace the existing RP mechanism.


>From the draft:

   Encapsulation and Decapsulation are expensive operations for routers
   and the latter, especially, as it entails a double lookup that many
   routers cannot do in hardware.  It is for this reason that several
   off the shelf chips do not support decapsulating the PIM Register
   packets.  Any router that cannot decapsulate the PIM Register packet
   in hardware must send all this traffic to CPU, where its
   decapsulated, and forwarded based on the multicast forwarding table.
   This increases the load on the CPU and also makes the router
   susceptible for DoS attacks.  Also, since Register packets are
   unicast, then can be easily spoofed and an attacker can use this to
   attack the router and thus the network.

   This document attempts to solve the above problems by doing away with
   the PIM Register packets.  It instead proposes using an MPLS tunnel
   to send all multicast data traffic till an SPT is formed.  This
   eliminates the complexity of decapsulating PIM register packets on
   the RP as it now only needs to pop off the MPLS labels before
   forwarding the native packet down the RPT.

Looks like the draft died some time back ..


On Thu, Dec 29, 2011 at 5:02 AM, Jeff Tantsura
<jeff.tantsura at ericsson.com> wrote:
> Mike,
> To my knowledge in most today's networks even if legacy equipment don't support IGMPv3 most likely 1st hop router does static translation and SSM upstream.
> The reason not to migrate to SSM is usually - ASM is already there and works just fine :)
> Cost to support RP infrastructure is usually the main non-technical factor to not to use ASM.
> Would be interested to hear from the SPs on the list.
> Regards,
> Jeff
> On Dec 28, 2011, at 2:19 PM, "Mike McBride" <mmcbride7 at gmail.com> wrote:
>> Marshall,
>> On Wed, Dec 28, 2011 at 1:50 PM, Marshall Eubanks
>> <marshall.eubanks at gmail.com> wrote:
>>> Dear Mike;
>>> On Wed, Dec 28, 2011 at 4:48 PM, Mike McBride <mmcbride7 at gmail.com> wrote:
>>>> Anyone using ASM (versus SSM) for IPTV? If so why?
>>> From what I understand, the answer is likely to be "yes" and the
>>> reason is likely to be "deployed equipment only
>>> supports IGMP v2."
>> Agreed. I'm seeking confirmation, from IPTV implementers, that non
>> igmpv3 support is the reason for using ASM with IPTV. Versus other
>> reasons such as reducing state. Or is this a non issue and everyone is
>> using SSM with IPTV?
>> thanks,
>> mike
>>> Regards
>>> Marshall
>>>> thanks,
>>>> mike

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