[j-nsp] Odd drop behavior on low-rate multicast streams

[John Neiberger]

On Mon, Oct 8, 2012 at 2:27 PM, John Neiberger <jneiberger at gmail.com> wrote:
> We have a simple setup like this:
>
> [receiver] ---- [ Cisco-rtr-A] ---- [ Cisco rtr-B] ----- [MX960] -----
> [Cisco rtr-C] ---- [source]
>
> The receiver has joined a specific S,G, but this is very low rate,
> perhaps just a couple of multicast packets per week. It's a multicast
> messaging setup related to emergency alerts. What's weird is that if
> you look at the multicast routing tables on the Cisco routers, the S,G
> will be there. However, the multicast route is not present on the
> Juniper router. It does show up under "show pim join", but there is no
> route. The odd behavior we're seeing is that the first message from
> source to receiver is always dropped. If we configure the source to
> send multiple times, the first one fails but all subsequent messages
> succeed. Our thought is that the multicast route is timing out on the
> MX 960, so the first packet gets dropped, although it apparently
> causes the route to be setup again since the rest of the packets
> succeed.
>
> Any idea if we're on the right track? It seems like we're just running
> into some sort of timeout issue on this router, but we're not sure
> yet.
>
> Thanks,
> John

I just ran across this configurable timeout value that I think might
be relevant. It looks like the max is 12 hours, so if this is the
right "knob", I don't think even maxing it out is going to help in our
situation.

timeout (Multicast)

Syntax

timeout minutes;
Hierarchy Level

[edit logical-routers logical-router-name routing-instances
routing-instance-name routing-options multicast forwarding-cache],
[edit logical-routers logical-router-name routing-options multicast
forwarding-cache],
[edit routing-instances routing-instance-name routing-options
multicast forwarding-cache],
[edit routing-options multicast forwarding-cache]
Release Information

Statement introduced in JUNOS Release 8.2.

Description

Configure the timeout value for multicast forwarding cache entries.

Options

minutes—Length of time that the forwarding cache limit remains active.

Range: 1 through 720