network protocols handbook.pdf

88Protocols GuideTCP/IP - Network Layer ProtocolsProtocol NameMZAP: Multicast-Scope ZoneAnnouncement ProtocolProtocol DescriptionMulticast-Scope Zone Announcement Protocol (MZAP) is forthe discovery of the multicast administrative scope zones thatare relevant at a particular location. MZAP also provides mechanismsto discover common misconfigurations of administrativescope zones.The use of administratively-scoped IP multicast allows packetsto be addressed to a specific range of multicast addresses suchthat the packets will not cross configured administrative boundaries,and also allows such addresses to be locally assigned andhence are not required to across administrative boundaries.The range of administratively-scoped addresses can be subdividedby administrators so that multiple levels of administrativeboundaries can be simultaneously supported. As a result, a“multicast scope” is defined as a particular range of addresseswhich has been given some topological meaning.Multicast Scope Zone Announcement Protocol (MZAP) allowsan entity to learn what scope zones it is within. Typically serverswill cache the information learned from MZAP and can thenprovide this information to applications in a timely fashion uponrequest using other means, e.g., via MADCAP. MZAP also providesdiagnostic information to the boundary routers themselvesthat enables misconfigured scope zones to be detected.All MZAP messages are sent over UDP, with a destination portof [MZAP-PORT] and an IPv4 TTL or IPv6 Hop Limit of 255.Protocol Structure8 9 16 24 32bitAddressVersion B PTYPENameCountFamilyMessage OriginZone ID AddressZone Start AddressZone End AddressEncoded Zone Name-1 (variable length)...Encoded Zone Name-N (variable length)Padding (if needed)• Version - The version number; currently defined as0.• B - Big Scope bit. 0 Indicates that the addresses inthe scoped range are not subdividable, and that addressallocators may utilize the entire range. If 1, addressallocators should not use the entire range, butshould learn an appropriate sub- range via anothermechanism.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 alladdresses in the packet. The families defined for IPare: 1: IPv4; 2: IPv6.• Name Count - The number of encoded zone nameblocks in this packet. The count may be zero.• Message Origin - The IP address of the interface thatoriginated the message.• Zone Start Address - The start address for the scopezone boundary. For example, if the zone is a boundaryfor 239.1.0.0 to 239.1.0.255, then the Zone StartAddress is 239.1.0.0.• Zone End Address - The ending address for thescope zone boundary. For example, if the zone is aboundary for 239.1.0.0 to 239.1.0.255, then the ZoneEnd Address is 239.1.0.255.• Zone ID Address - The lowest IP address of a boundaryrouter that has been observed in the zone originatingthe message. Together with the Zone StartAddress and Zone End Address, it forms a unique IDfor the zone. Note that this ID is usually different fromthe ID of the Local Scope zone in which the originresides.• Encoded Zone Name - Combined from the nextfields: D, LangLen, Language Tag, NameLen, ZoneName.Related protocolsIP, IPv6, UDPSponsor SourceMZAP is defined by IETF (http://www.ietf.org) in RFC 2776.Referencehttp://www.javvin.com/protocol/rfc2776.pdfMulticast-Scope Zone Announcement Protocol (MZAP)