Re: Multicas RPF check with multiple equal cost paths to the

Hi All,

Petr I would like to thank you for sharing such a valuable document!

The main points I understood are the following:

1. By default no load splitting will take place. When having two upstream
multicast neighbors on 2 subnets & having two equal cost routes to the
streamer in case of (S,G) or the RP in case of (*,G) the router will receive
the multicast traffic from the pim neighbor with the highest ip address.
Thus no load splitting will take place.

2. Load Splitting IP Multicast Traffic over equal cost routes can take place
in three modes:
a. Source Load Balancing: based on the source address For (S,G) S is the ip
address of streamer/ for (*,G) it is for the RP.
b. Source Group Load Balancing: Hash algorithm based on the Source & the
group address.
c. Source Group Next hop based balancing: This is the most effective method
as it prevents polarization problem, i.e. this is the only algorithm which
allows load balancing even within the same group.

Note that when both upstream routers & the downstream routers are on the
same subnet ECMP load balancing will not function due to the fact that this
has to do with the assert messages between the two upstream routers which
will lead to a forwarder election on the common subnet.

Please Gents send me your comments & correct me if any of the stated is
wrong.

Best Regards,

Karim Jamali

On Mon, Jan 18, 2010 at 7:05 AM, Petr Lapukhov
<petr_at_internetworkexpert.com>wrote:

> Hi,
>
> This is not a simple question, as it may seem at the first sight. By
> default, the RPF interface is selected among multiple equal-costs
> paths based on the PIM neighbor with the highest IP address (that is,
> assuming PIM is in use). This behavior could be changed using IP
> Multicast ECMP feature found in Cisco IOS. You may read more about
> this following this link:
>
>
> http://www.cisco.com/en/US/docs/ios/12_4t/ip_mcast/configuration/guide/mctlsplt.html
>
> It will explain the basic multicast multipath feature, various
> configuration options and multicast ECMP limitations. To me, it would
> be interesting to someone implementing unequal-cost multicast
> multipath based on Loop-Free-Alternatives or something similar. There
> was a lot of work implementing IP FRR for unicast traffic so it would
> seem reasonable to extended it for multicast traffic protection.
>
> HTH,
> --
> Petr Lapukhov, petr_at_INE.com
> CCIE #16379 (R&S/Security/SP/Voice)
>
> Internetwork Expert, Inc.
> http://www.INE.com <http://www.ine.com/>
> Toll Free: 877-224-8987
> Outside US: 775-826-4344
>
> 2010/1/17 Jorge Cortes <jorge.cortes.cano_at_gmail.com>:
> > Hi team,
> >
> > When a router that has multicast receivers directly attached to it has
> > multiple equal cost paths (interfaces) to get to the source of
> > multicast traffic, what is the criteria it uses to determine the
> > interface it will use for RPF? Or will all interfaces be valid RPF
> > interfaces?
> >
> > Regards,
> >
> > Jorge
> >
> >
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-- 
KJ
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