Cabletron Systems SmartSwitch manual Configuring Dvmrp TTL & Scope, Configuring a Dvmrp Tunnel

Chapter 12: Multicast Routing Configuration Guide

Configuring DVMRP TTL & Scope

For control over internet traffic, per-interface control is allowed through Scopes and TTL thresholds.

The TTL value controls whether packets are forwarded from an interface. The following are conventional guidelines for assigning TTL values to a multicast application and their corresponding SSR setting for DVMRP threshold:

TTL = 1	Threshold = 1	Application restricted to subnet
TTL < 16	Threshold = 16	Application restricted to a site
TTL < 64	Threshold = 64	Application restricted to a region
TTL < 128	Threshold = 128	Application restricted to a continent
TTL = 255		Application not restricted

To configure the TTL Threshold, enter the following command in Configure mode:

Configure the TTL Threshold.

dvmrp set interface <ip-addr>threshold <number>

TTL thresholding is not always considered useful. There is another approach of a range of multicast addresses for “administrative” scoping. In other words, such addresses would be usable within a certain administrative scope, a corporate network, for instance, but would not be forwarded across the internet. The range from 239.0.0.0 through 239.255.255.255 is being reserved for administratively scoped applications. Any organization can currently assign this range of addresses and the packets will not be sent out of the organization. In addition, multiple scopes can be defined on per-interface basis.

To prevent the SSR from forwarding any data destined to a scoped group on an interface, enter the following command in the Configure mode:

Configure the DVMRP scope.

dvmrp set interface <ip-addr>scope <ip-addr/mask>

Configuring a DVMRP Tunnel

The SSR supports DVMRP tunnels to the MBONE (the multicast backbone of the Internet). You can configure a DVMRP tunnel on a router if the other end is running DVMRP. The SSR then sends and receives multicast packets over the tunnel. Tunnels are CPU-intensive; they are not switched directly through the SSR’s multitasking ASICs.

204 SmartSwitch Router User Reference Manual