RE: RPF-Meanin

Dale's answer is fantastic. I just would add that the packet is also
compared against any static mroutes and multicast sources learned via MBGP
as well. If it matches based on either of these it will also _pass_ the RPF
check.

Cheers,
 
Jared Scrivener CCIE3 #16983 (R&S, Security, SP), CISSP
Sr. Technical Instructor - IPexpert, Inc.
URL: http://www.IPexpert.com
Telephone: +1.810.326.1444
Fax: +1.810.454.0130
Mailto: jscrivener_at_ipexpert.com

-----Original Message-----
From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On Behalf Of Dale
Shaw
Sent: Friday, 26 June 2009 5:08 AM
To: ismail mohamed
Cc: Cisco certification
Subject: Re: RPF-Meanin

Hi Ismail,

On Fri, Jun 26, 2009 at 1:20 PM, ismail mohamed<mmismail1979_at_gmail.com>
wrote:
> Hi,
> What is the meaning of RPF in Multicast ?

You should beef up on the RPF concepts in general, but here's a couple
of points on the RPF check:

- If a packet *destined* for a *multicast group address* arrives at an
interface, and that interface *is not* the interface the router would
use to reach the *source address* of the packet (by consulting the
unicast routing table), the packet _fails_ the RPF check.

- If a packet *destined* for a *multicast group address* arrives at an
interface, and that interface *is* the interface the router would use
to reach the *source address* of the packet (by consulting the unicast
routing table), the packet _passes_ the RPF check.

It's as simple as that.

I recommend reading 'Developing IP Multicast Networks' and the
multicast chapter in 'Routing TCP/IP vol. 2'.

cheers,
Dale

Blogs and organic groups at http://www.ccie.net
Received on Fri Jun 26 2009 - 06:03:45 ART