Multicast-Scope Zone Announcement Protocol (MZAP) is for the discovery of the multicast administrative scope zones that are relevant at a particular location. MZAP also provides mechanisms to discover common misconfigurations of administrative scope zones.
The use of administratively-scoped IP multicast, allows packets to be addressed to a specific range of multicast addresses such that the packets will not cross configured administrative boundaries, and also allows such addresses to be locally assigned and hence are not required to across administrative boundaries.
The range of administratively-scoped addresses can be subdivided by administrators so that multiple levels of administrative boundaries can be simultaneously supported. As a result, a "multicast scope" is defined as a particular range of addresses which has been given some topological meaning.
Multicast Scope Zone Announcement Protocol (MZAP) allows an entity to learn what scope zones it is within. Typically servers will cache the information learned from MZAP and can then provide this information to applications in a timely fashion upon request using other means, e.g., via MADCAP. MZAP also provides diagnostic information to the boundary routers themselves that enables misconfigured scope zones to be detected.
All MZAP messages are sent over UDP, with a destination port of [MZAP-PORT] and an IPv4 TTL or IPv6 Hop Limit of 255.
Protocol Structure
MSDP TLV format
| 8 bits | 9 bits | 16 bits | 24 bits | 32 bits |
| Version | B | PTYPE | Address Family | NameCount |
| Message Origin | ||||
| Zone ID Address | ||||
| Zone Start Address | ||||
| Zone End Address | ||||
| Encoded Zone Name-1 (variable length) | ||||
| ... | ||||
| Encoded Zone Name-N (variable length) | ||||
| Padding (if needed) | ||||
- Version - The version number; currently defined as 0.
- B - Big Scope bit. 0 Indicates that the addresses in the scoped range are not subdividable, and that address allocators may utilize the entire range. If 1, address allocators should not use the entire range, but should learn an appropriate sub- range via another mechanism.
- Packet Type - The packet types defined are:
0 : Zone Announcement Message (ZAM)
1 : Zone Limit Exceeded (ZLE)
2 : Zone Convexity Message (ZCM)
3 : Not-Inside Message (NIM) - Address Family - Identifies the address family for all addresses in the packet. The families defined for IP are: 1: IPv4; 2: IPv6.
- Name Count - The number of encoded zone name blocks in this packet. The count may be zero.
- Message Origin - The IP address of the interface that originated the message.
- Zone Start Address - The start address for the scope zone boundary. For example, if the zone is a boundary for 239.1.0.0 to 239.1.0.255,then Zone Start Address is 239.1.0.0.
- Zone End Address - The ending address for the scope zone boundary. For example, if the zone is a boundary for 239.1.0.0 to 239.1.0.255,then Zone End Address is 239.1.0.255.
- Zone ID Address - The lowest IP address of a boundary router that has been observed in the zone originating the message. Together with Zone Start Address and Zone End Address, it forms a unique ID for the zone. Note that this ID is usually different from the ID of the Local Scope zone in which the origin resides.
- Encoded Zone Name - Combined from the next fields: D, LangLen, Language Tag, NameLen, Zone Name.
Sponsor Source: MZAP is defined by IETF (http://www.ietf.org) RFC 2776.
Reference: http://www.javvin.com/protocol/rfc2776.pdf : Multicast-Scope Zone Announcement Protocol (MZAP)