The ONL NPR Tutorial

NPR Tutorial >> Filters, Queues and Bandwidth

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Multicast Filters

The NPR also supports multicast through filters where an incoming packet gets copied and forwarded to more than one output port. The main features of auxilliary filters are:

• Priority Selection: A multicast filter is selected like any other primary filter: the one with the highest priority (lowest number) is selected.
• Packet Copying: If a multicast filter is selected, enough copies of the matching packet are made so that copies can be directed to the output ports listed in the output ports box in the filter.

To demonstrate the packet-copying nature of multicast filters, we use the dumbbell network shown to the right and send ping packets from n1p3 to n2p2. At input port 1.3, we install both a route table and a multicast filter. The route table will direct packets over the solid red top path and the multicast filter will direct packets over both the dashed red middle path (output port 1.0) and the solid blue bottom path (output port 1.1). The effect of the multicast filter can be demonstrated by giving the multicast filter a higher priority than the route table and watching the bandwidth going out ports 1.0, 1.1 and 1.4 as you toggle the multicast filter on and off to demonstrate its effect.

The recipe for installing the multicast filter at input port 1.3 is:

• RLI Window:
  Select Port 1.3 => Configuration => Add Filter.

  The Add Filter dialogue box appears.

• Add Filter Dialogue Box:
  
  • Select * from the protocol menu to match any protocol.
  • Check the multicast box to make the filter a multicast filter
  • Enter 0,1 in the output ports box to direct matching packets to output ports 0 and 1.
  • Leave the default priority at 50 so that the filter has a higher priority than the route table which has priority 60.
  • Select Add

The bandwidth chart (right) shows that the traffic going out port 2.2 (solid magenta 2.2 tx curve) is double the bandwidth received at ports 2.0 (solid green 2.0 rx curve) and 2.4 (dashed red 2.2 rx curve) and the bandwidth transmitted at port 1.3 (solid black 1.0 tx curve). The chart clearly shows that there is traffic going over both the two links 1.0-2.0 and 1.1-2.4 that connect NPR 1 and NPR 2. But there is no traffic being received at port 2.1 (solid blue curve) where traffic would normally go if the route table were being selected.

The ping window below also shows that there are two copies of each packet received at n2p2. Not shown is the fact that the return traffic is actually traveling over the top 2.1-1.4 link as directed by the route table at port 2.2.

NPR Tutorial >> Filters, Queues and Bandwidth	TOC