I'm trying to understand how far I can push these 3560/3750 switches running ip base.
I know they now support OSPF -- which is great. But for ip multicast, they only support "PIM Stub Routing".
I've read and re-read the config guide. But I still don't completely understand. Quotes are from the config guide.
The IP base image contains only PIM stub routing. The IP services image contains complete multicast routing. On a switch running the IP base image, if you try to configure a VLAN interface with PIM dense-mode, sparse-mode, or dense-sparse-mode, the configuration is not allowed.
OK, so I can only configure full PIM mode on routed "uplinks" (physical ports configured with an ip address). SVI's (interface vlan x) can only have "ip pim passive".
In a network using PIM stub routing, the only allowable route for IP traffic to the user is through a switch that is configured with PIM stub routing.
Huh? Is that an attempt at saying the switch should be the user's default gateway? Or a default route must be learned through a physical routed uplink?
PIM passive interfaces are connected to Layer 2 access domains, such as VLANs, or to interfaces that are connected to other Layer 2 devices. Only directly connected multicast (IGMP) receivers and sources are allowed in the Layer 2 access domains. The PIM passive interfaces do not send or process any received PIM control packets.
OK, so if I have 2 SVI's on a switch (SVI x and SVI y) with "ip pim passive" configured on each, I can have a source in SVI x and a receiver in SVI y and shouldn't have a problem. IGMP is needed, but not PIM for this to work. Correct?
When using PIM stub routing, you should configure the distribution and remote routers to use IP multicast routing and configure only the switch as a PIM stub router. The switch does not route transit traffic between distribution routers. You also need to configure a routed uplink port on the switch. The switch uplink port cannot be used with SVIs. If you need PIM for an SVI uplink port, you should upgrade to the IP services feature set.
OK. That makes sense. Sacrifices must be made.
You must also configure EIGRP stub routing when configuring PIM stub routing on the switch.
What?!?!? Is there some special interaction between EIGRP stub routing and PIM stub routing? A default route through OSPF isn't good enough?
The redundant PIM stub router topology is not supported. The redundant topology exists when there is more than one PIM router forwarding multicast traffic to a single access domain. PIM messages are blocked, and the PIM asset and designated router election mechanisms are not supported on the PIM passive interfaces. Only the nonredundant access router topology is supported by the PIM stub feature. By using a nonredundant topology, the PIM passive interface assumes that it is the only interface and designated router on that access domain.
OK, since I can't have PIM neighbors on SVI interfaces, we can't have redundant "default gateways" for the subnet. With the stacks providing most of the redundancy, I can probably live with this.
The PIM stub feature is enforced in the IP base image. If you upgrade to a higher software version, the PIM stub configuration remains until you reconfigure the interfaces.
This makes sense.
