Term
| Explain the concept of TTL Scoping multicast traffic. |
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Definition
| One method for establishing boundaries to limit the scope of multicast traffic is to set a special filter on outgoing interfaces that checks the TTL value of all multicast packet. Only packets whose TTL value, after the normal decrement performed by the router, exceeds a configured threshold are forwarded, where all other multicast packets are dropped. |
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Term
| What are some of the limitations to implementing TTL scoping on a multicast network? |
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Definition
| For starters, TTL scoping is inflexible, since an interface's TTL threshold applies to all multicast packets. Another problem is that it is difficult to implement in all but the simplest topologies, and as your multicast internetwork grows in both scale and complexity, predicting the correct thresholds to contain and pass the correct sessions becomes a challenge. |
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Term
| Explain the concept of Administrative Scoping multicast traffic. |
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Definition
| Administrative scoping takes a different approach to bounding multicast traffic in that rather than filter on TTL values, a range of Class D addresses is reserved for scoping. |
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Term
| What is the reserved range of multicast addressing used for Administrative Scoping? |
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Definition
| The reserved range of multicast address is 239.0.0.0 - 239.255.255.255. Because this range is similar to the RFC 1918 addresses reserved for private use, it is important to set filters for 239.0.0.0 - 239.255.255.255 so that none of the addresses in that range are leaked into the public Internet. |
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Term
| How is the administratively scoped address space for multicasting be further subdivided in a heirarchical manner? |
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Definition
| The suggested range of 239.255.0.0/16 is allocated to local or site scope and the range of 239.192.0.0/14 for organization scope. |
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