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Multicast - Newbie Question

Hello Experts,

I'm new to Multicast and still on the porcess of learning the fundamental and undestanding the concepts. please ignore if this sounds a basic question.

I have two N3K switches Connected back to back via port-channel.

SW1 --------------------- SW2

On this lan segment, SW2 is the DR (configured higher priority). Between SW1 and SW2 i run ibgp.SW2 is configured as rp.

so when i source a traffic from sw1, then sw1 sends a pim join towards the rp(which is SW2) and then sw2 creates a (S,G) entry on its mrib table.

what i wanted to understand is, how is SW1 getting this S,G entry on its table?

My understanding  is, only the DR (on the source segement) and the rp gets the S,G entry when there are no clients / receivers attached.

since in this case DR and RP and the same, just wondering how SW1 gets this S.G entry.

please correct me if I went wrong in my understanding.

Thanks,

-Vijay

3 REPLIES 3
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Any inputs on this? or have i reached a wrong discussion forum?

Thanks,

-Vijay

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Hi Vijay,

If router configured for multicast-routing receives multicast traffic, it will create (S,G) entry. if it is configured for PIM-SM, it will also create (*,G) entry if it is not present

So in your case, you originated the traffic from SW1. So it will have (S,G) and (*,G)

/Raju

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Contributor

When you add an interface to a port channel group, Cisco NX-OS checks certain interface attributes to ensure
that the interface is compatible with the channel group. Cisco NX-OS also checks a number of operational
attributes for an interface before allowing that interface to participate in the port-channel aggregation.
The compatibility check includes the following operational attributes:
• Port mode
• Access VLAN
• Trunk native VLAN
• Allowed VLAN list
• Speed
• 802.3x flow control setting
• MTU
• Broadcast/Unicast/Multicast Storm Control setting
• Priority-Flow-Control
• Untagged CoS
Use the show port-channel compatibility-parameters command to see the full list of compatibility checks
that Cisco NX-OS uses.
You can only add interfaces configured with the channel mode set to on to static port channels. You can also
only add interfaces configured with the channel mode as active or passive to port channels that are running
LACP. You can configure these attributes on an individual member port.
When the interface joins a port channel, the following individual parameters are replaced with the values on
the port channel:
• Bandwidth
• MAC address
• Spanning Tree Protocol
The following interface parameters remain unaffected when the interface joins a port channel:
• Description
• CDP
• LACP port priority
• Debounce
After you enable forcing a port to be added to a channel group by entering the channel-groupforce command,
the following two conditions occur:
• When an interface joins a port channel, the following parameters are removed and they are operationally
replaced with the values on the port channel; however, this change will not be reflected in the running
configuration for the interface:
• QoS
• Bandwidth
• Delay
• STP
• Service policy
• ACLs
• When an interface joins or leaves a port channel, the following parameters remain unaffected:
• Beacon
• Description
• CDP
• 802.3x flow control setting
• MTU
• Broadcast/Unicast/Multicast Storm Control setting
• Priority-Flow-Control
• Untagged CoS
Use the show port-channel compatibility-parameters command to see the full list of compatibility checks
that Cisco NX-OS uses.
You can only add interfaces configured with the channel mode set to on to static port channels. You can also
only add interfaces configured with the channel mode as active or passive to port channels that are running
LACP. You can configure these attributes on an individual member port.
When the interface joins a port channel, the following individual parameters are replaced with the values on
the port channel:
• Bandwidth
• MAC address
• Spanning Tree Protocol
The following interface parameters remain unaffected when the interface joins a port channel:
• Description
• CDP
• LACP port priority
• Debounce
After you enable forcing a port to be added to a channel group by entering the channel-groupforce command,
the following two conditions occur:
• When an interface joins a port channel, the following parameters are removed and they are operationally
replaced with the values on the port channel; however, this change will not be reflected in the running
configuration for the interface:
• QoS
• Bandwidth
• Delay
• STP
• Service policy
• ACLs
• When an interface joins or leaves a port channel, the following parameters remain unaffected:
• Beacon
• Description
• CDP

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