Multicast Tunnel Example

Creating Multicast Tunnels on a DIGITAL Network


In the example below, there is one connection to the Internet through an Internet Service Provider (ISP). This ISP provides a Multicast traffic tunnel. Multicast traffic is that which uses the address space above 224.0.0.0 and below 238.0.0.0. Multicast traffic is different from Unicast (point-to-point) traffic in that it is a one-to-many type of traffic that routers will forward.

A router will only forward Multicast traffic onto an adjacent router if that router has a client that wishes to see multicast traffic. DIGITAL routers require DVMRP (Distance Vector Multicast Routing Protocol) to be enabled on the interfaces to which you will forward multicast traffic.



Creating a Multicast Tunnel

In the example above there is a multicast tunnel originating from the ISP at 22.254/24. This tunnel has a preset endpoint of 22.1/24. A multicast tunnel needs to be set up on Gateway 1 to point towards 22.254/24.

  1. Initiate a clearVISN IP Switch Manager session to Gateway 1 (GW-1). In this example we will use Gateway 1 as the starting point.
  2. Click .
  3. Click the Multicast Tunnels link.
  4. Enter in the Destination IP Address edit box: 205.226.24.254.
  5. Click .
  6. Enter in the Local Address edit box: 205.226.24.1.
  7. (Optional) Define the time-to-live (TTL) threshold for the multicast datagram. Enter in the Threshold edit box: 128.
    We use 128 for the purpose of broadcasting. A 128 TTL is what is defined as Internet broadcast.
  8. (Optional) Define the maximum amount of bandwidth for all multicast traffic forwarded along the tunnel. Currently not supported.
  9. (Optional) Define the cost of the tunnel. Enter in the Metric edit box.
    This is used to show the route preference. It is usually good to leave this as the default unless there are many other multicast tunnels present in your network.
  10. Click .
  11. Perform steps 1 through 9 with address reversed on the exit point for the multicast tunnel. In this example the ISP has already done this for us.
  12. Ensure that DVMRP is running on all interfaces (Ethernet, ATM, FDDI) on which the multicast is to be received. See Configuring DVMRP.




Copyright © 1997 Ipsilon Networks, Inc.
Portions copyright © Digital Equipment Corporation 1998. All rights reserved.
Updated January 8, 1998
Send comments to Digital Equipment Corporation, doc-quality@lkg.mts.dec.com