From CCIE Study Wiki
Multicast scoping confines the forwarding of multicast traffic to a group of routers, limiting how far multicast traffic will travel in a network.
Theory
You can scope the multicast traffic by TTL value or administratively by using filters.
- With multicast TTL scoping, routers compare the TTL value on a multicast packet with a configured TTL value on each outgoing interface. A router forwards the multicast packet only on those interfaces whose configured TTL value is less than or equal to the TTL value of the multicast packet.
- Administratively scoped multicast addresses are those in the 239.0.0.0 to 239.255.255.255 range. Used to limit the forwarding of multicast traffic outside of a domain.
The ip multicast boundary command can be used to filter out multicast traffic destined for a RP or a specific group
Commands
- ip multicast boundary access-list [filter-autorp] (interface) - Command to filter multicast traffic to specific groups or a RP.
Default Settings
- Default interface TTL value is 0
Verification
Troubleshooting, Tips, and Tricks
- There's no way to tweak TTL multicast scoping so that it applies to some multicast packets but not others!
- You should configure and apply filters on a router's interface so that multicast traffic with group addresses in the private address range are not allowed to enter or exit the interface.
Online Resources
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