Posted on January 9, 2021 8:19 am
 |  Asked by Oliver Ettlin
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I’m working in a PTP Network. My Arista are serving as PTP boundary Clocks, but i’ve got also other Switches in my Network which are not PTP aware.
How can I tell my Aristas that they Send out IGMP Joins to the Other Switches for the PTP Multicast (At the moment i’ve made static routes, but it would be the nicer solution when the aristas would send out IGMP Joins for the PTP Multicast).


Thanks in advance for your Help

Answered on January 9, 2021 8:28 am

Hi Oliver,

Thanks for reaching out.

As per current implementation/working scenario, we need to have IGMP static join config on corresponding interfaces in order to transport PTP messages to multicast group :

Sample config:

interface Vlan10
ip address
ip igmp static-group --------------------> Static join for the PTP multicast group
ip pim sparse-mode

Also from the following TOI it states the below:

Both Transparent and Passive devices require additional configuration in order to forward the PTP stream. If a device must also manage a control-plane flow (and hence has a dependency on the control traffic), this can also reduce the accuracy of PTP. Due to this, and as the capability for a PTP node to send Joins/Reports is not included in the IEEE specification (1588-2008), the Arista distribution of PTP does not send IGMP reports or PIM joins from enabled nodes. This means that when there are L3 devices in the path that are not configured as Boundary Clocks additional configuration is necessary to complete the multicast flow.




Posted by Oliver Ettlin
Answered on January 10, 2021 12:09 pm

Hey Bhavana

Thanks for your very good Answer and explanation

ip igmp static-group works only in PIM mode, but not in my Layer 2 environment.

I've found out, that
ip igmp host-proxy does the Job, but is this a sober solution?



Answered on January 12, 2021 6:53 am

Hi Oliver,

Thank you.

"ip igmp static-group" -->yes you are correct. This command sends out a *,g  join towards the RP, which is L3 and involves Pim.

However "ip igmp host-proxy" command always generates reports since it is static and sends it out.
Could you please confirm if you have a receiver in your network environment?if yes then do they send active reports?
Also incase if we have a receiver then we can make use of "snooping" on the L2 switch.

However before we suggesting , we would like to understand your multicast setup details and flow.




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