Prerequisites For Ip Multicast Load Splitting - Ecmp - Cisco Catalyst 3650 Configuration Manual

IP Multicast Optimization: IP Multicast Load Splitting across Equal-Cost Paths

Prerequisites for IP Multicast Load Splitting - ECMP

• You must have an adequate number of sources (at least more than two sources) to enable ECMP multicast
load splitting based on source address.
• You must have multiple paths available to the RP to configure ECMP multicast load splitting.
• When using PIM-SM with shortest path tree (SPT) forwarding, the T-bit mus be set for the forwarding
of all (S, G) states.
• Before configuring ECMP multicast load splitting, it is best practice to use the show ip rpf command
to validate whether sources can take advantage of IP multicast multipath capabilities.
• BGP does not install multiple equal-cost paths by default. Use the maximum-paths command to configure
multipath (for example in BGP). For more information, see the
Splitting, on page 323
Restrictions
• If two or more equal-cost paths from a source are available, unicast traffic will be load split across those
paths. However, by default, multicast traffic is not load split across multiple equal-cost paths. In general,
multicast traffic flows down from the RPF neighbor. According to PIM specifications, this neighbor
must have the highest IP address if more than one neighbor has the same metric.
• The ip multicast multipath command does not support configurations in which the same PIM neighbor
IP address is reachable through multiple equal-cost paths. This situation typically occurs if unnumbered
interfaces are used. Use different IP addresses for all interfaces when configuring the ip multicast
multipath command.
• The ip multicast multipath command load splits the traffic and does not load balance the traffic. Traffic
from a source will use only one path, even if the traffic far outweighs traffic from other sources.
Enabling ECMP Multicast Load Splitting Based on Source Address
Perform this task to enable ECMP multicast load splitting of multicast traffic based on source address (using
the S-hash algorithm) to take advantage of multiple paths through the network. The S-hash algorithm is
predictable because no randomization is used in calculating the hash value. The S-hash algorithm, however,
is subject to polarization because for a given source, the same hash is always picked irrespective of the device
on which the hash is being calculated.
OL-29890-01
Note Use the show ip route command with either the IP address of the source for the
ip-addressargument or the IP address of the RP to validate that there are multiple paths
available to the source or RP, respectively. If you do not see multiple paths in the output
of the command, you will not be able to configure ECMP multicast load splitting.
section.
IP Multicast Routing Configuration Guide, Cisco IOS XE Release 3SE (Catalyst 3650 Switches)
Enabling ECMP Multicast Load Splitting
Use of BGP with ECMP Multicast Load
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