IEEE 802c:2017 pdf free download – IEEE Standard for Local and Metropolitan Area Networks:Overview and Architecture
8.4.1 Concept and overview
The U/L bit of a local MAC address is set to 1, indicating that the remaining bits (i.e., all bits except the U/Lbit and the I/G bit, which is set as described in 8.2.2) are locally administered. Local MAC addresses are notpresumed globally unique across all IEEE 802 networks. The locally administered bits of local MACaddresses are arbitrarily assignable under the condition that local MAC addresses are unique within a LAN(which may be a bridged LAN or virtual bridged LAN).In a virtual bridged LAN wherein the bridges useIndependent VLAN Learning， the uniqueness condition applies to each VLAN rather than to the entirevirtual bridged LAN.Any failure of such uniqueness invalidates the fundamental premises of IEEE 802network operation and may lead to disruption.Therefore, administrators should ensure that the probabilityof local MAC address non-uniqueness is acceptably small.
While a local administrator may assign addresses throughout the local range, the optional Structured LocalAddress Plan (SLAP) specifies different assignment approaches in four specified regions of local MACaddress space.
Unlike universal addresses, which are persistent to the MAC entity, local MAC addresses are not necessarilypersistent.The local MAC address assigned to a MAC entity，including any subsequent change to thatassignment, is entirely within the scope of the local administration.
8.4.2 Local MAC address assignment protocols
An address assignment protocol assigning local MAC addresses to devices on a LAN should ensureuniqueness of those addresses, per the description of F.1.2 of IEEE Std 802.1Q. That standard’s Annex Falso identifies risks of non-uniqueness.
When multiple address assignment protocols operate on a LAN without centralized administration, addressduplication is possible even if each protocol alone is designed to avoid duplication. When multiple addressassignment protocols operate on a LAN without centralized administration, address duplication is possible,even if each protocol alone is designed to avoid duplication, unless such protocols assign addresses fromdisjoint address pools.
The subclauses below specify the usage of local MAC address space according to the SLAP.Administratorswho deploy multiple protocols on a LAN in accordance with the SLAP will enable the unique assignment of local MAC addresses within the LAN as long as each protocol maintains unique assignments within its ownaddress subspace.
8.4.3 Structured Local Address Plan(SLAP)
The SLAP specifies use of local MAC address space.Under the SLAP, the use is specified differently infour quadrants of local MAC address space.
The least and second least significant bits of the initial octet of a MAC address are designated the M bit andX bit, respectively, using the terminology specified in the IEEE RA “Guidelines for Use OrganizationallyUnique ldentifier (OUI) and Company ID (CID)” [Ba]. The third and fourth least significant bits of theinitial octet in the local MAC address are designated the Y bit and Z bit, respectively, as illustrated for a48-bit address in Figure 11a (see NOTE 4 of 8.2.2).