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How to configure PIM sparse mode on EXOS

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TitleHow to configure PIM sparse mode on EXOS
Correctly configure PIM-SM on EXOS.

Before we configure PIM-SM we need to understand PIM, and the different jobs that a PIM router can be configured for.  PIM stands for Protocol Independent Multicast, which means that PIM needs a working L3 routable network before you start configuring PIM.  PIM is responsible for forwarding multicast over a L3 routable network. With this being said, you must have both PIM-SM and IPMCforwarding enabled on any VLAN that you want your L3 multicast to traverse.  In PIM-SM you also need to have a Bootstrap Router (BSR), and a Rendezvous Point (RP) in your network.  Below is a description of the BSR, RP, and what each role does.  There are other roles elected in the background but, this article explains the configured roles.

Note: Every PIM router does not have to be a CRP or CBSR, but each PIM domain needs at least one of each or have  static CRP configured.
  • CRP (Candidate Rendezvous Point) - Configuring PIM CRP enables the PIM router to advertise it's candidacy to be a RP for a list of multicast streams in your configured policy file.  The policy file will be a list of multicast address ranges that this RP will service.  The lower CRP priority corresponds to a higher priority.   If elected as a RP the PIM router serves two functions.  It will be the location where PIM routers register new multicast streams that this RP is servicing, and a location where PIM routers look for the stream the RP is servicing.  You can have many RP's, one can service and another could service  You can also have two service the same range for redundancy.
    • Note: think of the RP as a OSPF DR.  It gets all new multicast streams (similar to an OSPF DR receiving all LSA's), and only sends the stream when a PIM router asks for it.
  • CBSR (Candidate Bootstrap Router) - Configuring PIM CBSR enables the PIM router to advertise it's candidacy to be a BSR.  If elected as a BSR it will be responsible for providing all PIM routers with the IP of each RP and which multicast streams they are servicing.  This is how PIM routers know what RP to go to for multicast streams.

  • PIM-SM
  • EXOS
1.  Make sure unicast routing is working for all multicast paths.

2.  Make sure IGMP and IGMP snooping is enabled
enable igmp
enable igmp snooping

3.  Enable IPMC forwarding on all vlans that multicast will need to be routed.  (It's like IP forwarding for multicast)
enable ipmcforwarding <vlan>

4.  Enable PIM-SM on the same VLANs that IPMC forwarding was enabled on.
configure pim add <vlan> sparse

5.  Select and configure your CRP.  You should have the RP close to where most of your streams are coming from.
  1. Create your policy file that tells PIM what streams it will be the RP for. 
Switch# vi rp_list.pol

##Example RP List for, and
entry rp_list {
if match any {
then {
  1. Configure the CRP.  The VLAN you select will be the advertised location of the RP.
configure pim crp <vlan> rp_list

6.  Select and configure your CBSR.  The IP of the VLAN you chose will be used in the BSR election.
configure pim cbsr <vlan>

7.  Enable PIM
enable pim

Additional notes
PIM configured Priority election:
  • CBSR priority - Numerically higher priority value wins
  • CRP priority - Numerically lower priority value wins

Show commands for Multicast and PIM:
  • show pim
  • show pim rp-set
  • show pim cache
  • show pim cache <group address>
  • show mcast cache
  • show igmp snooping <vlan>
  • debug hal show ipv4mc gaddr <group address>




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