From: Alex (alex.arseniev@gmail.com)
Date: Fri Sep 15 2006 - 10:46:53 ART
If I understand the problem correctly, SW1-R1 link carries only VLAN1
traffic. Same for SW1-R2 link: it carries only VLAN1 traffic.
Similarly, SW2-R1 link carries only VLAN2 traffic and SW2-R2 link also
carries only VLAN2 traffic. R1 forwards mcast traffic between own
interafces: from VLAN1 on SW1 to VLAN2 on SW2 because it is a receiver's DR.
In this case, shortly after the "primary" link (I get it as SW2-R1 link is
primary) on SW2 fails then R1 is no longer directly connected to VLAN2 on
SW2 and ceases to be a receiver's DR on VLAN2.
R2 will assume role of receiver's DR and will start to forward traffic from
its interface in VLAN1 on SW1, to another interface directly connected to
VLAN2 on SW2.
HTH
Cheers
Alex
----- Original Message -----
From: "Geert Nijs" <geert.nijs@simac.be>
To: <ccielab@groupstudy.com>
Sent: Friday, September 15, 2006 11:33 AM
Subject: Multicast problem
> 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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