Multicast questions - PIM passive & IGMP

[ChrisNewnham_]

Hello, 2 questions about multicast:

1) When configuring PIM passive, can you configure it on the source router, destination router, and intermediate nodes? I believe you can.

2) I believe IGMP is only required to be configured on the destination device, however many SSM examples I've seen show IGMPv3 being configured on the source device as well - is this really required?

Thanks

[Joseph W. Doherty]

Ever hear how to parse "assume"?  If not, send me a private msg and I'll explain.  ; )

Yes, wholly agree there's a context of SSM and IGMPv3, being discussed, but reread how your post begins, your initial context appears to apply to multicast as a whole, at least it does to me.  I wanted to insure other readers didn't think that was intended, and by your reply, it was not so intended because you assumed they would take what you wrote in the context you've just described.

"But really, in 2023, why would anyone use anything but PIM-SSM?"

ROFL, sorry, but that question, to me, is like the (supposed) quote "Let them eat cake.".  (Laugh, now I'm guilty of assuming you, and others, know the context of quote I provided.)

[Ramblin Tech]

Hi Joe,

I am reminded of a Dr. House line from the TV series "House, M.D." when Dr. Cutty tells him about "assuming"...

Anyway, I am not trying to quibble, but I am serious about PIM-SSM being everyone's first choice for a new mcast application. I don't believe Cisco has recommended PIM-DM since the 1990's, and Beau Williamson's caveman expression from back then, "Dense mode bad. Sparse mode good", should be updated to "SSM better". No flood & prune, no RPs, no group address conflicts, harder for a rogue source to inject mcast content, with the only PIM-SSM downside I see being legacy IGMPv1/2 configurations on receivers' first-hop routers that have to be dealt with. It may just be that the SP mcast apps that I have been exposed to are not representative of broader, enterprise mcast apps, but I honestly do not see any operational advantage to bringing up a new mcast application using dense or sparse (w/RP) mode.

I'll temper my question slightly: if you don't have legacy IGMPv1/2 configurations, and given that PIM-SSM has been around for 20 years, why would anyone use anything but PIM-SSM?

[Joseph W. Doherty]

Ramblin, on technical merits, I don't believe there's anything to quibble about concerning the merits of SSM.

If you had written SSM should be everyone's first choice for new multicast deployments, if environment supports it, I would agree.  But that's not what you just wrote.

"It may just be that the SP mcast apps that I have been exposed to are not representative of broader, enterprise mcast apps . . ."

Now that, I believe is very likely!!!

My prior job was as a Comcast enterprise network engineer.  With 100,000 enterprise users, it was a fairly good size enterprise network, yet a totally different usage environment from Comcast's Internet and video distribution network, also fairly good sized too.

Within the latter network, multicast was very relevant, and, unsurprisingly, SSM 1st choice.

Within the enterprise network, need for multicast was rare, and if needed, you might still be running on 20 year old, or older, equipment.  (Heck, during one of our enterprise equipment upgrades we found the replacement device's ports didn't correctly work at 10Mbps/half-duplex!  Laugh, and if you think upgrade the host, sure until you find out there is no such upgrade and it's indispensable.)

Basically the SP network was close to state-of-the-art, while the enterprise network, often, would use whatever continues to work.  From a business perspective, the SP network is a profit center, the enterprise network a cost center.