From: Geert Nijs (geert.nijs@simac.be)
Date: Fri Sep 15 2006 - 07:33:23 ART
Hello group,
I am stuck with the following simple topology and the multicast problem i am facing.
Two core routers R1 and R2 are connected with a VLAN 3, vlan3 is running pim mc routing
Two edge switches SW1 and SW2 are connected to R1 and R2 with two uplink ports each.
all users on SW1 are connected into VLAN1
all users on SW2 are connected into VLAN2
VLAN1 and VLAN2 are present on R1 and R2, but they are not trunked across the link between R1 and R2. R1 is HSRP master for all vlans
and R2 is HSRP backup for all vlans. VLAN1 and VLAN2 are also running pim mc.
R1 and R2 are configure with an anycast Rendez-Vous point and an MSDP peering runs between R1 and R2
(i am sure you all CCIE candidates are familiar with this setup :-)
R1 -- VLAN 3 ---- R2
| \ / |
| \ / |
| \ / |
SW1 & SW2
Suppose the mc server is on SW1 and the receiver is on SW2. The mc stream goes from SW1 to R1 and from R1 to SW2
The problems begin when the primary uplink of SW2 fails. On R1, VLAN2 goes down, and R1 learn a route to VLAN2 from R2.
Basically, VLAN2 changes from being a connected vlan to being a routed vlan via R2. For unicast there is no problem.
However, the multicast stream will also be forwarded on vlan3 towards R2. However, since R2 still has an active (albeit HSRP passive) interface
in VLAN1 (the source of the mc steam), the mc stream arriving on VLAN3 will fail the RPF check and the mc stream is broken........
My main concern about this is that you always are going to have this problem with switches that have double uplinks for redundancy purposes, so
how to make mc work in such failure scenarios ?
regards,
Geert
CCIE #13729
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