PIM Support on Extreme Networks Devices

Key Features

Key features of PIM-SM are the following:

• Uses IGMP to propagate group membership information
• Sends hello messages to determine neighbor presence and configuration
• Sends join/prune messages to determine the need to retain multicast route information for a particular group on an interface
• Sends assert messages to resolve conflicts that occur regarding inbound interfaces
• Uses routes in the Multicast Routing Information Base (MRIB) to perform its reverse path forwarding check

Key features of PIM-SSM are the following:

• Protects against Denial of Service Attacks from unwanted sources
• Is easier to provision and maintain due to the single source address that a receiver can request data from
• Provides the ideal mechanism for internet broadcasts that originate from a single source and go to multiple receivers
• Does not require unique multicast addresses; it depends upon the receiver request for the destination address of the broadcast

Key features of PIM-DM are the following:

• Ease of configuration
• Operational and overhead efficiencies when a high density of network PIM enabled router interfaces have receivers attached for a given multicast data stream

PIM-SM Message Types

Extreme Networks PIM-SM-enabled devices use the following message types:

• Hello — These messages announce the sender‘s presence to other PIM-SM devices. The hello packet includes options such as:
  • Hold time — the length of time to keep the sender reachable
  • Designated router (DR) priority — used to designate which PIM-SM device will act on behalf of sources and receivers in the PIM-SM domain
• Register — These messages are used by a source‘s DR to encapsulate (register) multicast data, and send it to the rendezvous point (RP) — a PIM-SM router designated as the root of a shared tree.
• Register-Stop — These messages are used by the RP to tell the source‘s DR to stop registering traffic for a particular source.
• Join/Prune (J/P) — These messages contain information on group membership received from downstream routers.

  PIM-SM adopts RPF technology in the join/prune process. When a multicast packet arrives, the router first judges the correctness of the arriving interfaces:

  • If the packet is a source address/multicast group (S,G) entry (on the shortest path tree (SPT)), then the correct interface is the reverse path forwarding (RPF) interface towards the source.
  • If the packet is not an S,G entry (on the RP tree (RPT)), then the correct interface is the RPF interface towards the RP.

    A router directly connected to the hosts is often referred to as a leaf router or DR. The leaf router is responsible for sending the prune messages to the RP, informing it to stop sending multicast packets associated with a specific multicast group. When the RP receives the prune message, it will no longer forward the multicast traffic out the interface on which it received the prune message.

• Assert — These messages indicate that the device received a data packet on its outbound (receiving) interface for the group. They report the metric or distance to the source or RP to help the device identify the most direct path to the root of the tree. If multiple routers claim to have the most direct path to the source or RP, each device sends its own assert message and the router with the best metric wins. The other device will then remove that link from its outbound interface list for the group.
• Bootstrap — These messages are sent by the PIM-SM router that has been elected as the bootstrap router (BSR) to inform all PIM-SM routes of the RP/group mappings.
• Candidate RP message — These messages are sent by the configured candidate RP routers to the BSR to inform the BSR of its RP/group candidacy.

PIM-SSM Message Types

The PIM-SSM implementation is a subset of PIM-SM protocol. PIM-SM and PIM-SSM can coexist on a single router and are both implemented using the PIM-SM protocol.

Extreme Networks PIM-SSM enabled devices use the following PIM-SM message types:

• Hello — These messages announce the sender‘s presence to other PIM-SM devices. The hello packet includes options such as:
  • Hold time — the length of time to keep the sender reachable
  • Designated router (DR) priority — used to designate which PIM-SM device will act on behalf of sources and receivers in the PIM-SM domain
• Join/Prune (J/P) — These messages contain information on group membership received from downstream routers.
• PIM-SM adopts RPF technology in the join/prune process. When a multicast packet arrives, the router first judges the correctness of the arriving interfaces:
  • If the packet is a source address/multicast group (S,G) entry (on the shortest path tree (SPT)), then the correct interface is the reverse path forwarding (RPF) interface towards the source.
• Assert — These messages indicate that the device received a data packet on its outbound (receiving) interface for the group. They report the metric or distance to the source to help the device identify the most direct path to the root of the tree. If multiple routers claim to have the most direct path to the source, each device sends its own assert message and the router with the best metric wins. The other device will then remove that link from its outbound interface list for the group.

PIM-DM Message Types

The PIM-DM-enabled devices use the following message types:

• Hello — These messages announce the sender‘s presence to other PIM-DM devices. The hello packet includes options such as:
  • Hold time — the length of time to keep the sender reachable
• Join/Prune (J/P) — These messages contain information on group membership received from downstream routers.
• Graft – These messages are sent upstream when new group membership is added to a pruned branch, instructing the upstream router to forward multicast data for the specified source to the downstream router.
• Graft ACK – These messages are sent to the downstream router, acknowledging the reception of a graft message from the downstream router.
• State Refresh – These messages are generated periodically by the PIM-DM router directly connected to a source and sent to neighbor routers. State refresh message minimize network overhead by conveying prune state.