Subject: [magma] IGMP Router State information

From: "Manikantan Srinivasan" <[email-masked]>
Date: Mon, 12 Sep 2005 10:24:07 +0530

Hello

I have the following question and thanks in advance for your reply.

The question is related to the IGMP State maintained by multicast routers
and the availability of the state information to the end users (Example CLI
output)

When a router state becomes Exclude (A*B,B-A), (i.e when the router receives
an IS_EX (B) and its current state is INCLUDE (A)), How should the multicast
group table information get displayed in the user output (Ex CLI)?

Let me use a specific example, Suppose the router initially receives from a
Host H1 an IS_IN (for group 224.1.1.1 , for source 192.168.6.1) on an
interface, and subsequently receives from a Host H2 an IS_EX (for group
224.1.1.1, for sources 192.168.6.1, 192.168.6.2), the expected changed state
is EXCLUDE (192.168.6.1, 192.168.6.2). How should the router state
information be made available in the user output (example CLI)?

I have come across two types of implementation

The first type is shown below.
==========================================================
Router#show ip igmp group 224.1.1 detail
 
Interface: Ethernet0/0
Group: 224.1.1.1
Uptime: 00:00:01
Group mode: EXCLUDE (Expires: 00:02:59)
Last reporter: 192.168.2.2

Source Address   Uptime    v3 Exp   CSR Exp   Fwd
192.168.6.1      00:00:01  00:02:58  stopped   No
192.168.6.2      00:00:00  stopped   stopped   No
Router#
==========================================================

In this case the timer for 192.168.6.1 is active. There is no active timer
for 192.168.6.2.

The second type is shown below
==========================================================
#show ip multicast group
Total 2 Groups
Group Address   Source Address  Interface  Mode    Life
---------------+---------------+---------+-------+-------
224.1.1.1       192.168.6.2        3      exclude   257
224.1.1.1       192.168.6.1        3      include   255

#
==========================================================

As per standards (RFC 3376) Section 6.3 Page 29, for a 
Group filter mode EXCLUDE, TIMER > 0, we have a suggestion to forward
The traffic to the source (whose timer is > 0)

As per standards (RFC 3376) Section 6.4.` Page 30, for a notation
EXCLUDE (A, B) A is a set of source records, whose timer is > 0
(sources that at least one host has requested to be forwarded).

Hence as per standards, (for my example) the router can forward 
Traffic received from source 192.168.6.1. Does it mean the mode
Is "INCLUDE"?

Assume both implementations are as per the requirements of the standard
IS the CLI output "implementation specific"? i.e in the second
Type shown above, the mode "include" provides clarity to the end user
That the data from that source will be forwarded.

Thanks 

Best regards
Mani

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