A link aggregation (e.g., as set forth in IEEE 802.3ad) is a computer networking term which describes using multiple links (e.g., Ethernet network cables and/or ports in parallel) as one logical port to increase the link speed beyond the limits of any one single link and/or to provide for link redundancy between two network elements. Other terms used for link aggregation may include link bonding, link bundling, and/or link aggregation group (LAG). LAG will be used hereinafter to refer to link aggregation. A LAG may be provisioned between a pair of network elements, either locally or virtually. A LAG in a network element may span ports in the same packet processing line card or across packet processing line cards, providing protection against processing line card failure.
A LAG permits two network elements interconnected by the LAG to communicate simultaneously over all member links in the LAG. Network datagrams may be dynamically distributed across member links in the LAG based on a local rule so that administration of what datagrams actually flow across a given port may be taken care of automatically with the LAG.
A LAG, as set forth in IEEE 802.3ad, allows one or more links to be aggregated together to form a LAG. Once implemented, the LAG can be configured and reconfigured quickly and automatically with no risk of duplication or rendering of frames, and with minimum packet loss.
A LAG may be used to provide load balancing across multiple parallel links between two network devices. One method of load balancing used today is based on Internet Protocol (IP) header source and destination addresses. Another method, which may be used for non-IP protocols carried in Ethernet frames, is based on media access control (MAC) source and destination addresses. In typical networks, the load may not be divided equally among the links of a LAG. The statistical nature of traffic distribution across parameters (e.g., IP addresses) used by typical hashing algorithms may result in overloading certain links in the LAG while underutilizing other links in the LAG.
A LAG may provide local link protection. Should one of the multiple member links used in a LAG fail, network traffic (e.g., datagrams) may be dynamically redirected to flow across the remaining surviving links in the LAG. A LAG may redirect traffic to a surviving link based on a hashing algorithm. However, there is no upfront prediction of what traffic gets redirected over which link, and it is not predictable what link in the LAG may fail. In point-to-point Ethernet applications where a virtual local area network (VLAN) identifier (ID) is used to identify a connection between two edge Ethernet switches, the hashing can be made on the VLAN and/or other Ethernet header and/or payload information (e.g., IP header information if the Ethernet payload contains an IP packet). This may make it difficult to predict a load on a given link in the LAG, and may make it difficult to efficiently and predictably design an Ethernet network that provides packet-loss and bandwidth service level agreement (SLA) guarantees for point-to-point services. Point-to-point services known as ELine (Ethernet Private Line (EPL) or Ethernet Virtual Private Line (EVPL)) may be the most stringent services in terms of SLAs.
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