nanog mailing list archives

Re: IP Multicast Persistent Duplicate Packet Issue


From: Roman Islam <romislam () gmail com>
Date: Thu, 7 Apr 2022 09:07:34 +1000

Thanks Jared. Yes it is SSM. I will try to flip PIM priority and align HSRP
active.

My initial thought was keeping everything as it is. Can I simply flip PIM
assert winner to PE1. Same way we can manually select STP root. Looks like
this is probably not an option. Didn't find relevant doc on how to
manipulate PIM assert winner in Cisco boxes though. Highest IP is the
winner if IGP costs are the same to the source.

R


On Thu, Apr 7, 2022 at 3:02 AM Jared Mauch <jared () puck nether net> wrote:

If this is ASM, what device is the RP?  You may want to configure MSDP
between PE1/PE2 to help if that’s the case, or is this SSM or something
else you may want to just flip the PIM priority to make it pick what you
want and see if you can tie it to your HSRP (Cisco, might I suggest VRRP so
you could do dual-vendor later?) state, perhaps with EEM script to keep the
config in sync if required.

- Jared

On Apr 6, 2022, at 3:25 AM, Roman Islam <romislam () gmail com> wrote:

Hi Everyone,

Has anyone experienced a TETRA Radio application issue if underlying IP
multicast transport sends persistent duplicate packets?

Here is my scenario as below:

PIM is running on the MPLS L3 VPN environment. C multicast is running on
a single VRF (TETRA) only. Source is running behind a dual home PE. HSRP,
PIM DR path is via PE1 to the source. Anycast RP is configured with PE1 &
PE2.

On the receiver side there is a single PE. When I check (S,G) route on
the receiver side PE default MDT is working as expected. After the
threshold exceeds it switches to the data MDT. PIM Assert mechanism winner
is PE2 though (Since PE 2 has the highest IP and source is behind dual home
PE with equal cost I guess).

Can this be a reason for persistent duplicate multicast packets at the
receiver side; since the assert winner is PE2 but HSRP, PIM DR path is via
PE1 to the source?

If this is the case is there any way to manually configure the assert
winner to PE1?

Roman



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