Multicast PIM-DM (finishing)

PIM-DM Basics

PIM-DM uses five RIMv2 messages

• Hello

• Join/Prune (Add/CUT)

• Graft grafting)

• Graft-ACK (OK)

• Assert (Declaration)

The PIMv2 router uses the Hello message to discover the neighbor, when the PIMv2 router PIM-SM or PIM-DM) is active, will periodically send the Hello Message on each interface configured with PIM; PIMv1 vro has similar functions, but uses Query messages. A Hello (or Query) message contains a storage time holdtime, which specifies the maximum time for a neighbor to wait for receiving the next message before declaring that the router is invalid. In Cisco IOS Software, the default PIMv2 Hello interval PIMv1Query interval is 30 seconds. You can use the command ip pim query-interval to modify the default interval according to the interface, the retention time is automatically set to 3.5 times the Hello/Query interval.

PIMv2 messages are sent to 224.0.0.13 with the Protocol Number 103), while PIMv1 messages are sent to 224.0.0.2 with the Protocol Number 2)

When multicast sources start to send multicast packets, the PIM-DM uses the flood/clipping protocol to build multicast trees. When each PIM-DM router receives a multicast packet, it adds a table item in its own forwarding table, and the multicast packet is routed to all the leaf routers-that is, there is no downstream PIM neighbor router. If the leaf router that receives the multicast packet is not connected to any group member. Then the vro must cut itself out of the multicast tree. Therefore, you need to send a Prune (CUT) message to the upstream neighbor along the Multicast Source Direction. The destination address of the Prune message is 224.0.0.13, And the upstream neighbor address is also encoded in the message. If the upstream neighbor does not connect to the group member to which the multicast package belongs, and no other downstream neighbor or receives a message from all its downstream neighbors, the router sends a Prune message along the upstream neighbor of the multicast source.

The Graft message is sent to the upstream neighbor of the multicast tree in Unicast mode. When the upstream router receives the Graft message, it adds the interface that receives the message to its egress interface list, so that the interface enters the forwarding status, and immediately sends the Graft-ACK (grafting confirmation) message to its new downstream neighbor. If the vro is forwarding multicast packets to other downstream neighbors, you do not need to perform any further operations. However, if the vro already exists, you must also want your upstream neighbor to send the Graft message. After the vro sends the Graft message, it will wait for 3 seconds to wait for the Graft-ACK message. However, if the confirmation message is not received within 3 seconds, the vro will need to re-transmit the Graft message.

This article is from the "industry diligence and waste in Taobao" blog, please be sure to keep this source http://sxsure.blog.51cto.com/2166161/1275917