From: Ivan (ivan@iip.net)
Date: Fri Sep 15 2006 - 11:44:05 ART
In my understanding trouble not in flow vlan2 > sw2 > r2 > r1 > sw1 > vlan1,
but in flow vlan1 > sw1 > r1 > r2 > sw2 > vlan2.
Trouble appear at this place r1 > r2. Becauce RPF-check failed. VLAN1 directly
connected to r2, thus RPF-interfase will r2(vlan1) not r2(vlan3). But packet
received on interface r2(vlan3).
On Friday 15 September 2006 17:46, Alex wrote:
> 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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-- Ivan
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