Cisco – Multicast Distribution with PIM

ciscoigmpmulticastpim

I have to receive some multicast groups for an IPTV platform. I can't use PIM (they don't give me an RP address for the groups…). The provider suggested me to do a join to each multicast group and then distribute the multicast from my switch to the receivers (via PIM), which are in a different VLAN than the interface where i do the join.

Now I have my switch subscribed to some multicast groups but my receivers can't join the group.

My switch configuration is something like:

interface Vlan10
 ip address X.X.X.X 255.255.255.224
 ip pim sparse-mode
 ip igmp join-group 234.X.X.X
!
interface Vlan20
 ip address 192.168.20.1 255.255.255.0
 ip pim sparse-mode
!

My receivers are in VLAN 20 and I join the Provider groups in the VLAN 10.

Any suggestion or idea to get this working?

I attach an scheme to clarify.

The Mcast Provider 2 is working with PIM without problems and now I have a subscription to a MCAST from provider 1 via join command and would like to receive it in my receivers in vlan 62
enter image description here

Best Answer

Remember that "ip igmp join-group" will cause all multicast packets for this group to be forwarded also to the CPU. Probably this is not what you want. Instead talk to your provider and tell them to use "ip igmp static-group" on their side.

Related Solutions

Cisco – IGMP snooping and link-local multicast addresses

I've kept digging around the internet....and I think I've answered my own question.
Now I need to go back to the application/device owners/developers and see what we can do or further lock these devices down to their own VLAN.

Please leave comments or answers with any further advice.

RFC 4541 2.1.2:

Packets with a destination IP address outside 224.0.0.X which are not IGMP should be forwarded according to group-based port membership tables and must also be forwarded on router ports.

This is the main IGMP snooping functionality for the data path. One approach that an implementation could take would be to maintain separate membership and multicast router tables in software and then "merge" these tables into a forwarding cache.
Packets with a destination IP (DIP) address in the 224.0.0.X range which are not IGMP must be forwarded on all ports.

This recommendation is based on the fact that many host systems do not send Join IP multicast addresses in this range before sending or listening to IP multicast packets. Furthermore, since the 224.0.0.X address range is defined as link-local (not to be routed), it seems unnecessary to keep the state for each address in this range. Additionally, some routers operate in the 224.0.0.X address range without issuing IGMP Joins, and these applications would break if the switch were to prune them due to not having seen a Join Group message from the router.

Vlan – Setting up PIM Sparse mode

My questions are:

Should we setup on our core network switch OSPF with a router ID of 1.1.1.1 and then not set any OSPF settings on any other switch?

OSPF is not necessary for this implementation.

Would PIM Sparse Mode only need to be enabled on the core switches or on all of the switches in the network?

Pim-SM needs to be enabled on each L3 interface on which you want to allow the multicast traffic. For example, if you wish to contain the traffic to Vlans 15 and 14, you would have to do the following on your core:

configure
ip multicast
ip igmp
ip pim sparse
interface vlan 14
ip igmp
ip pim
interface vlan 15
ip igmp
ip pim
exit

If you want the traffic to traverse all Vlans, then you will need the appropriate interface configuration under each Vlan. Your L2 switches will need IGMP snooping turned on (ideally on all interfaces via the global configuration).

configure
ip igmp snooping 
bridge multicast filtering

For a very basic multicast setup like this, these should be the only features that you would need.

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