[nsp] anycast DR interaction?

From: Leon Cozzi (Leon.Cozzi@uk.didata.com)
Date: Wed Mar 27 2002 - 07:23:01 EST


I have a scenario I am trying to get an explanation to regarding 2 PIM DR's
running as anycast RP's attached to a LAN. Basically I cannot understand how
PIM,IGMP operates in the scenario below with the respect to the forwarding
of source traffic from a multi-access segment. The PIM standard states that
the DR will forward traffic onto and off a multi-access segment, but in the
scenario below the non-dr takes over the forwarding of source traffic from
the multi-access segment, when link A fails. Can anyone explain what PIM is
doing is this scenario as I cannot see any procedural details in the PIM
standard.

Thanks in advance

Leon Cozzi

In the following scenario when both A and B links are available both the
source tree and the shared tree are built along link A.
                        
                                 ------------
                                    |Pigpen | ip igmp join-group
                                 ------------ 239.255.1.1
                                / \
                                   / \
                                          / \
                                             / A \B
                                            / \
                                           / \
                                          / \
        RP ------------- ------------ RP
        1.1.1.1 | Maggie | MSDP | Lisa |
1.1.1.1
                          --------------- ------------
        10.159.71.194 | DR |10.159.71.193
                             | |
                                   | |
                        ------------------------------------------
                                                      Source to 239.255.1.1

The PIM standard states that a DR will forward traffic onto and off a LAN.
In the scenario above, the DR Maggie will forward traffic from its Ethernet
interface and out of link A.

maggie#sh ip mroute active
Active IP Multicast Sources - sending >= 4 kbps

Group: 239.255.1.1, (?)
   Source: 10.159.71.150 (?)
     Rate: 10 pps/10 kbps(1sec), 10 kbps(last 25 secs), 8 kbps(life avg)

lisa#sh ip mroute active
Active IP Multicast Sources - sending >= 4 kbps
lisa#

When I fail link A, Lisa take over the forwarding of the traffic after
pigpen sends a join up link B.

lisa#sh ip mroute active
Active IP Multicast Sources - sending >= 4 kbps

Group: 239.255.1.1, (?)
   Source: 10.159.71.150 (?)
     Rate: 10 pps/10 kbps(1sec), 10 kbps(last 36 secs), 2 kbps(life avg)

maggie#sh ip mroute active
Active IP Multicast Sources - sending >= 4 kbps
maggie#

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