CCNP Enterprise Core (350-401)
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Rendezvous Points
In PIM Sparse Mode, it is required that one router or more operate as a rendezvous point, or RP. The RP is a single common root placed at a selected point of a shared distribution tree. The RP can be configured statically or learned through a dynamic mechanism. The PIM router can be configured to…
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PIM Assert Mechanism
There can be scenarios in a multicast network where duplicate multicast packets can flow onto the network. There is a mechanism in PIM called the ‘PIM assert mechanism’ that can stop these duplicate flows. This mostly happens in PIM Dense Mode networks due its flooding properties, and rarely happens in PIM Sparse Mode. A PIM…
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Reverse Path Forwarding (RPF)
Reverse Path Forwarding is an algorithm that helps prevent loops and ensures that multicast traffic arrives on the correct interface. The RPF algorithm has several features: When a router receives a multicast packet on an interface that it uses to send unicast packets towards the source, that interface is a RPF interface. When a packet…
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PIM Sparse Mode – Designated Routers
Where there are multiple PIM-SM routers on a subnet, an election is called to determine a designated router (DR). The designated router helps prevent duplicates of multicast traffic from being sent to to the rendezvous point. In an election between PIM sparse mode routers, the highest priority wins the election. By default the priority of…
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PIM Sparse Mode
PIM sparse mode was designed for networks where multicast receivers are sparsely located across subnets on the network. PIM spare mode also works quite well in dense multicast receiver environments too. PIM sparse mode uses the unicast routing table to carry out reverse path forwarding checks, and can utilise any routing protocol that populates the…
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PIM Shortest Path Tree Switchover
PIM sparse mode allows the last hop router to switch from the shared tree to a shortest path tree for a specific source. This is a default behaviour in Cisco routers and happens after the first multicast packet is received from the rendezvous point from the shared tree, even if the shortest path is through…
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Multicast Source Sparse Mode Registration
When the source for the group sends a packet, the first hop router attached to that source is required to register the source with the rendezvous point. The rendezvous point is also requested to build a tree back towards the first hop router. The first hop route encapsulates multicast data from the source into a…
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PIM Dense Mode
PIM dense mode constructs the multicast tree by flooding traffic out of every interface from the source to every dense mode router across the network. PIM dense mode is a suitable configuration where receivers of the multicast group are located across every subnet on the network. It is applicable to small networks, but not recommended…
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PIM Operating Modes
There are five operating PIM modes: PIM Dense Mode (PIM-DM) PIM Spare Mode (PIM-SM) PIM Spare Dense Mode PIM Source Specific Multicast (PIM-SSM) PIM Bidirectional Mode (Bidir-PIM) PIM Control messages are sent using IP Protocol 103. Register and register stop messages can be sent using unicast, or multicast with a time-to-live of 1 to all…
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PIM Terminlogy
Reverse Path Forwarding (RPF) Interface The reverse path forwarding interface is the interface with the lowest cost path to the IP address of the root of the shortest path tree (the source of the multicast stream). The lowest cost is based on the factors of administrative distance and metric. If there are multiple interfaces with…