Dell Force10 S4810P - Multicast with ECMP; Implementation Information

710 | Multicast Features
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Multicast with ECMP
Dell Force10 multicast uses Equal-cost Multi-path (ECMP) routing to load-balance multiple streams
across equal cost links. When creating the shared-tree Protocol Independent Multicast (PIM) uses routes
from all configured routing protocols to select the best route to the rendezvous point (RP). If there are
multiple, equal-cost paths, the PIM selects the route with the least number of currently running multicast
streams. If multiple routes have the same number of streams, PIM selects the first equal-cost route returned
by the Route Table Manager (RTM).
In Figure 33-1, the receiver joins three groups. The last-hop DR initially has two equal-cost routes to the
RP with no streams, so it non-deterministically selects Route 1 for the Group 1 IGMP Join message. Route
1 then has one stream associated with it, so the last-hop DR sends the Group 2 Join by Route 2. It then
non-deterministically selects Route 2 for the Group 3 Join since both routes already have one multicast
stream.
Figure 33-1. Multicast with ECMP
Implementation Information
• Because protocol control traffic in FTOS is redirected using the MAC address, and multicast control
traffic and multicast data traffic might map to the same MAC address, FTOS might forward data traffic
with certain MAC addresses to the CPU in addition to control traffic.
Gig A
IGMP Group Table
Group Address Interface
Group 1 GigabitEthernet A
Group 2 GigabitEthernet A
Group 3 GigabitEthernet A
Gig X
Gig Y
Gig B
Source Receiver
RP
IGMP Group Table
Group Address Interface
Group 1 GigabitEthernet Y
Group 2 GigabitEthernet X
Group 3 GigabitEthernet X
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3
Gig Z
Gig W
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