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MC-LAG, or Multi-Chassis Link Aggregation Group, is a type of link aggregation group (LAG) with constituent ports that terminate on separate chassis, primarily for the purpose of providing redundancy in the event one of the chassis fails. The IEEE 802.1AX-2008 industry standard for link aggregation does not mention MC-LAG, but does not preclude it. Its implementation varies by vendor; notably, the protocol existing between the chassis is proprietary. In 2012 the IEEE created a standardized alternative to MC-LAG in IEEE 802.1aq (Shortest Path Bridging). == Link Aggregation Group (Background) == A LAG (Link Aggregation Group) is a method of inverse multiplexing over multiple Ethernet links, thereby increasing bandwidth and providing redundancy. It is defined by the IEEE 802.1AX-2008 standard, which states, “Link Aggregation allows one or more links to be aggregated together to form a Link Aggregation Group, such that a MAC client can treat the Link Aggregation Group as if it were a single link." This layer 2 transparency is achieved by the LAG using a single MAC address for all the device’s ports in the LAG group. LAG can be configured as either static or dynamic. Dynamic LAG uses a peer-to-peer protocol for control, called Link Aggregation Control Protocol (LACP). This LACP protocol is also defined within the 802.1AX-2008 standard. LAG can be implemented in two ways. LAG N and LAG N+N. LAG N is the load sharing mode of LAG and LAG N+N provides the worker standby flavour. The LAG N protocol automatically distributes and load balances the traffic across the working links within a LAG, thus maximising the use of the group if Ethernet links go down or come back up, providing improved resilience and throughput. For a different style of resilience between 2 nodes, a complete implementation of the LACP protocol supports separate worker/standby LAG subgroups. For LAG N+N, the worker links as a group will fail over to the standby links if any one or more or all of the links in the worker group fail. Note, LACP marks links as in standby mode using an “out of sync” flag. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「MC-LAG」の詳細全文を読む スポンサード リンク
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