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Chapter 8: Multicast Routing Configuration Guide
148 SmartSwitch Router User Reference Manual
Configure 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. 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:
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 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.
Configure the TTL Threshold.
dvmrp set interface
<ip-addr>
threshold
<number>
Configure the DVMRP scope.
dvmrp set interface
<ip-addr>
scope
<ip-addr/mask>