Re: RPF check procedures

Hi,

The answer for your question is YES

Auto-RP relies on a router designated as RP mapping agent. RP's announce
themselves to the mapping agent, and it resolves any conflicts.

The mapping agent then sends out the multicast group-RP mapping information
to the other routers. specific groups used are 224.0.1.39 and .40. The first
(.39) is used to advertise, the second (.40) is used for discovery.

** 224.0.1.39  CISCO-RP-ANNOUNCE (Auto-RP)
** 224.0.1.40  CISCO-RP-DISCOVERY (Auto-RP)

Routers perform an RPF check to ensure that arriving multicast packets were
received through the interface that is on the most direct path to the source
that sent the packets. After the router receives a multicast packet, it
performs an RPF check. If the RPF check succeeds, the packet is forwarded;
otherwise, it is silently discarded.

R2(config)#access-list 101 permit ip any 224.0.1.0 0.0.0.255
R2(config)#^Z
R2#deb ip pa
%SYS-5-CONFIG_I: Configured from console by console
R2#deb ip pac de 101
IP packet debugging is on (detailed) for access list 101
IP: s=10.1.23.3 (FastEthernet1/1), d=224.0.1.40, len 28, rcvd 0, proto=2
pak 65788FD0 consumed in input feature , packet consumed, MCI Check(59),
rtype 0
, forus FALSE, sendself FALSE, mtu 0
R2#
IP: s=3.3.3.3 (FastEthernet1/1), d=224.0.1.39, len 48, input feature
    UDP src=496, dst=496, MCI Check(59), rtype 0, forus FALSE, sendself
FALSE, m
tu 0
FIBipv4-packet-proc: route packet from FastEthernet1/1 src 3.3.3.3 dst
224.0.1.3
9
FIBfwd-proc: Default:224.0.0.0/4 multicast entry
FIBipv4-packet-proc: packet routing failed
R2#

And for the multicast fee:

In PIM Dense Mode Protocol, When data arrives on a non-Reverse Path
Forwarding (non-RPF) interface (that is, an interface that is not used to
reach the source) and the interface is point-to-point (p2p), a Prune message
is immediately sent to the upstream neighbor in an attempt to shut off the
flow of traffic. Note that when data arrives on a non-RPF interface that is
not a p2p (that is, multiaccess) interface, an Assert is triggered instead
of a Prune.

In PIM Sparse mode uses the explicit join model whereby receivers send PIM
Join messages to a designated rendezvous point (RP). (The RP is the root of
a shared distribution tree down which all multicast traffic flows.) To get
multicast traffic to the RP for distribution down the shared tree, first-hop
routers with directly connected senders send PIM Register messages to the
RP. Register messages cause the RP to send an (S, G) join toward the
source, so that multicast traffic may flow natively to the RP via an
shortest-path tree (SPT) and hence down the shared tree.
Routers may be configured with an SPT threshold, which, once exceeded, will
cause the last-hop router to join the SPT. This action will result in the
multicast traffic from the source to flow down the SPT from the source
directly to the last-hop router.
Reverse Path Forwarding (RPF) check is done differently, depending on tree
type.
 ** If traffic is flowing down the shared tree, the RPF check mechanism will
use the IP address of the RP to perform the RPF check.
 ** If traffic is flowing down the SPT, the RPF check mechanism will use the
IP address of the source to perform the RPF check.

thanks,
Victor Cappuccio
CCIE R/S# 20657
CCSI# 30452
www.anetworkerblog.com
www.linkedin.com/in/vcappuccio

On Sat, May 30, 2009 at 9:53 AM, Sergei Udovenko <udovenko_at_gmail.com> wrote:

> Hello, GS!
> Need some clarification on subject.
>
> Are there any RPF checks between MA and cRP too (if yes, who "RPFs" who?),
> or only from clients to the MA(when MA announcing RP mapping) and after
> that
> from client to the RP itself, and is there any RPF check to the source
> AFTER
> all this steps?
>
> p.s. Basically there are 3 RPF checks from the client towards MA, RP,
> Source
> am I right?
>
>
> --------------------
> Best regards,
> Sergei
>
>
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