nx.os.and.cisco.nexus.switching.2nd.edition.1587143046

For the Layer 2 multicast communication between senders and receivers between data
centers, the Layer 2 multicast traffic must go across the OTV overlay network. Because you
have multicast-enabled transports, you do not have suboptimal head-end replication to
support Layer 2 multicast communication between multiple data centers for application
server requirements. Source Specific Multicast (SSM) is used for the data plane application
Layer 2 Multicast requirements. The SSM multicast is different than the ASM Multicast
groups for the OTV control-plane adjacencies. For the data-plane requirements with
multicast-enabled transport; a multicast source is activated on the data center and starts
streaming traffic to the multicast-group (G). The local OTV edge device receives the first
multicast frame and creates a mapping between the group Gs and a specific SSM group Gd
available in the transport infrastructure; the multicast group from source (Gs) is mapped to
SSM data group (Gd). The range of SSM groups to be used to carry Layer 2 multicast data
streams are specified during the configuration of the overlay interface.
To configure the range of an SSM data, use the following command under the overlay
interface created in the OTV VDC:
OTV-VDC-A(config-if)# otv data-group 232.1.1.0/26
You need to plan for the amount of data-group multicast and multicast state. For the data
grouping, a single data group can be used in the core to carry all the (S,G) site multicast
streams; the remote sites would receive all the streams as soon as a receiver joined a
specific group. If a dedicated data group were used for each (S,G) site group, each site
would receive multicast traffic only for the specific groups joined by local receivers.
For Unicast-enabled transport, multicast capabilities are not enabled in the transport
infrastructure. This means that the Layer 2 multicast traffic can be sent across the OTV
overlay where the multicast source is located; this results in head-end replication. IGMP
Snooping ensures that the Layer 2 multicast packets are sent only to remote data centers
where there are active receivers; IGMP Snooping reduces the amount of required head-end
replication.
OTV and QoS
To clarify the behavior of OTV from a QoS perspective, you should distinguish between
control- and data-plane traffic:
• Control plane: The control plane frames are always originated by the OTV Edge
Device and statically marked with CoS = 6/DSCP = 48.
• Data plane: The assumption is that the Layer 2 frames received by the Edge Device
to be encapsulated have already been properly marked (from a CoS and DCSP
perspective).
When OTV encapsulates the packet, the QoS marking transfers to the header of the
encapsulated packet in the following two ways:
• With 802.1p tagged packets the L2-CoS is copied to the outer DSCP, and the inner
DSCP is preserved as is across the overlay.
• With 802.1p untagged packets the outer DSCP is zero (TOS = 0x00) and the inner