Simulate Multicast

Source-Specific Multicast (SSM)

A Source-Specific Multicast (SSM) is a multicast forwarding method that

  • delivers multicast packets to receivers only from a specified source address requested by the receiver

  • reduces resource requirements and improves security by restricting sources, and

  • is specified by an (S,G) parameter per multicast flow.

The (S,G) pair is labeled using a dot-decimal notation similar to IP addresses (for example, 1.1.1.1, 2.2.2.2). Each (S,G) pair is the name of a multicast flow, and each flow is listed in the Multicast flows table.

Discovered versus simulated multicast flows

How you work with multicast flows within Cisco Crosswork Planning differs depending on whether Cisco Crosswork Planning discovered the multicast flow or you are simulating it (Table 1).

Table 1. Discovered versus simulated multicast flows

Discovered multicast flow

Simulated multicast flow

Creation

Cisco Crosswork Planning discovers multicast flows—(S,G) pairs)—and multicast traffic is derived from the Multicast Flow Traffic table.

First, manually create the multicast flow, defining both the source (S) and the destinations (G). Next, create a demand that links the source to these multicast destinations, allowing the routing to be simulated through the network.

Hops

Each discovered multicast flow includes multicast flow hops, which are node-interface combinations through which the multicast path flows.

When you create a demand, it determines the path to take.

External hops

Cisco Crosswork Planning discovers multicast flow hops on interfaces that are external to the plan file. These are interfaces from a plan node to an external node, or from an external node to a plan node.

When you create a demand, it determines the path to take, but multicast external flow hops are not identified.

Destinations

Cisco Crosswork Planning does not identify a list of multicast destinations for each flow.

Specify destinations (nodes, interfaces, external ASes, or external endpoints) when you create multicast flows. When creating multicast demands, specify these as multicast destinations.

Applicable tables

  • Multicast flows

  • Multicast flow hops

  • Multicast flow external hops

  • Multicast flows

  • Multicast flow destinations

  • Demands

Configure multicast flow hops for simulations

Cisco Crosswork Planning uses the network state in multicast simulation. Use this task to set simulations to consider multicast flow hops.

If a plan file contains multicast information, it includes the current hops taken by multicast flows. You can specify that Cisco Crosswork Planning multicast simulations should use these flow hops if possible. This is useful, for example, when calculating incremental routing changes on the current network state, such as those caused by a failure. For planning purposes, when the current state is not relevant, you can change this behavior to disregard the multicast flow hops.

Procedure

Step 1

Open the plan file (refer to Open plan files). It opens in the Network Design page.

Step 2

In the toolbar, click or choose Actions > Edit > Network options.

Step 3

Click the Simulation tab.

Step 4

To use or disregard multicast flow hops in simulation, check or uncheck Use multicast flow hops, and click Save.

Configure Cisco next hop for multicast flows

Use this task to set Cisco Crosswork Planning to use Cisco next hops.

For manually inserted demands, all SSM demand traffic for the (S,G) pair (multicast flow) goes through any interface that is traversed by that demand.

However, you can set Cisco Crosswork Planning to use Cisco next hops, which are calculated using a hash on S and G for a multicast flow (S,G). The hash calculation is different in IOS and IOS XR. The default behavior is that of IOS. The IOS XR hash is used on all nodes whose OS field starts with IOS XR.

Procedure

Step 1

Open the plan file (refer to Open plan files). It opens in the Network Design page.

Step 2

In the toolbar, click or choose Actions > Edit > Network options.

The Network options page opens.

Step 3

Click the Protocols tab.

Step 4

Under the Multicast section, from the Multipath selection drop-down list, choose CiscoNextHop.

Step 5

Save your changes.

Multicast demands

A multicast demand is a network traffic requirement that

  • specifies how multicast flows are to be handled within a network simulation

  • can be inserted manually for discovered multicast flows, and

  • must be created manually for simulated multicast flows.

Simulated multicast demands

For manually inserted demands, all SSM demand traffic for the (S,G) pair (multicast flow) goes through any interface that is traversed by that demand. SSM demands are routed to take the shortest path from the destination to the source, rather than from the source to the destination, as unicast demands do. By default, multicast multipath is disabled. If two paths of equal cost exit from a node on the route back to the source, the path is chosen based on:

  • The remote interface with the highest IP address is used.

  • If IP addresses are not available, the router name with the lowest lexicographical name is used.

However, you can set Cisco Crosswork Planning to use the Cisco next-hop multicast, multipath selection method. For more information, refer to Configure Cisco next hop for multicast flows.

The sources of these multicast demands can be nodes, interfaces, external ASes, or external endpoints. Using interfaces lets you specify the exact interface on which demand traffic is entering. Using external endpoints lets you model situations where the multicast source is outside of the nodes in the plan, and there is more than one possible entry point of the traffic flow into and through the interfaces in the plan.

In this example, the selected demand has a node source of AMS, and a multicast destination containing two nodes: FRA and PAR. The source node (S) is marked by A, and the destinations in the receiver group (G) are marked by Z.

Topology example

You can model a source that is outside the plan using external endpoints. In this example, the demand’s source is an external endpoint that contains AMS and LON as members. The multicast destination includes both FRA and PAR.

View multicast flows

To view sources and destinations of multicast demands, select the demand from its table. The source is identified in the plot by A and the destinations are identified by Z.


Note

You can only view the Multicast flow details in the UI if it's already present in your plan file. You cannot create, edit, or delete the multicast flows from the UI.

To view...

Show this table

Multicast flows, including both source and receiver names

Multicast flows

Discovered multicast flow hops, including (S,G) name, hop node, and hop interface

Multicast flow hops

Discovered multicast flow external hops (destinations that are inferred as external to the plan), including (S,G) name, direction of the outbound interface

Multicast flow external hops

User-created multicast flow destinations, including (S,G) name and destination node

Multicast flow destinations

Multicast demands

Demands

Create demands for multicast flows

Use this task to create demands for multicast flows.

Procedure

Step 1

Open the plan file (refer to Open plan files) with Multicast details. The plan file opens in the Network Design page.

Step 2

From the toolbar, choose Actions > Insert > Demands > Demand.

Alternatively, in the Network Summary panel, click Add icon > Demands in the Demands table.

Step 3

In the Name field, enter the name of the demand.

Step 4

In the Source section, define the source (S) of the multicast flow.

  1. From the Type list, select the source as a node, interface, external AS, or external endpoint.

  2. For node sources, select both the site and the node.

    For interface sources, select the site, node, and the interface.

    For external ASes, select both the external AS and the node within the plan file through which this external traffic flows.

    For external endpoints, select its name.

Step 5

In the Destination section, define the receiver group (G) of the multicast flow.

  1. From the Type list, choose Multicast destination.

  2. From the (G) Receiver list, choose the receiver that identifies the simulated multicast flow (S,G).

Step 6

Optionally, complete all other fields as needed and then click Add.