Port Aggregation Protocol (PAgP) is a

Cisco Systems Cisco Systems, Inc., commonly known as Cisco, is an American-based multinational corporation, multinational digital communications technology conglomerate (company), conglomerate corporation headquartered in San Jose, California. Cisco develo ...

proprietary networking protocol In telecommunications, a proprietary protocol is a communications protocol owned by a single organization or individual. Intellectual property rights and enforcement Ownership by a single organization gives the owner the ability to place restricti ...

, which is used for the automated, logical aggregation of

Ethernet Ethernet () is a family of wired computer networking technologies commonly used in local area networks (LAN), metropolitan area networks (MAN) and wide area networks (WAN). It was commercially introduced in 1980 and first standardized in ...

switch ports, known as an

EtherChannel EtherChannel is a port link aggregation technology or port-channel architecture used primarily on Cisco switches. It allows grouping of several physical Ethernet links to create one logical Ethernet link for the purpose of providing fault-toleran ...

. The PAgP is proprietary to

. A similar protocol known as LACP — released by the

IEEE The Institute of Electrical and Electronics Engineers (IEEE) is a 501(c)(3) professional association for electronic engineering and electrical engineering (and associated disciplines) with its corporate office in New York City and its operati ...

and known as 802.3ad or

802.1ax In computer networking, link aggregation is the combining ( aggregating) of multiple network connections in parallel by any of several methods, in order to increase throughput beyond what a single connection could sustain, to provide redundan ...

recently — is an industry standard and is not tied to a specific vendor. PAgP

messages A message is a discrete unit of communication intended by the source for consumption by some recipient or group of recipients. A message may be delivered by various means, including courier, telegraphy, carrier pigeon and electronic bus. A ...

are always sent to the well known Cisco

multicast In computer networking, multicast is group communication where data transmission is addressed to a group of destination computers simultaneously. Multicast can be one-to-many or many-to-many distribution. Multicast should not be confused wit ...

address 01-00-0C-CC-CC-CC with protocol type code 0x0104. PAgP uses the same multicast group

MAC address A media access control address (MAC address) is a unique identifier assigned to a network interface controller (NIC) for use as a network address in communications within a network segment. This use is common in most IEEE 802 networking tec ...

of CDP.

Cisco implementation

PAgP can be configured on a Cisco switch to operate in three different modes: * ''auto'' - passive negotiation of the channel * ''desirable'' - active negotiation of the channel * ''on'' - no protocols are used: it assumes the other side has enabled

link aggregation In computer networking, link aggregation is the combining ( aggregating) of multiple network connections in parallel by any of several methods, in order to increase throughput beyond what a single connection could sustain, to provide redundan ...

. On Cisco network devices running CatOS, a single switch module may only be configured to run in either LACP or PAgP modes. Cisco devices that run

IOS iOS (formerly iPhone OS) is a mobile operating system created and developed by Apple Inc. exclusively for its hardware. It is the operating system that powers many of the company's mobile devices, including the iPhone; the term also include ...

(native and/or non-hybrid mode boxes) support individual port configuration for LACP and are not restricted to per module settings as with CatOS.

Limitations

A limitation of Port Aggregation Protocol is that all the physical ports in the aggregation group must reside on the same switch. Cisco's 6500 and the 4500E platforms, remove this limitation using Virtual Switching System (VSS), which allows port channels to be split between two chassis.

Advantages

With Port Aggregation Protocol "the line speed of an agport is the total of the line speeds of each of its physical ports." This does not automatically means that a single transfer will use all of the aggregated interfaces bandwidth; rather, this depend on the distribution method of choice. Most Cisco switches use src/dst MAC address hash as distribution method, meaning that a single session will use the bandwidth of a single interface. Other Cisco switches uses a proprietary distribution method which enable true frame round-robin, enabling maximum link speed to be the same as the sum of the interfaces composing the aggregation group. This mean packet order can be altered, however. Plain EtherChannel load-balancing works by having the switch assign a hash result from 0-7 based on the configured hash method (load-balancing algorithm) for the type of traffic. This hash result is commonly called a Result Bundle Hash (RBH). They are then divided out over the available links. Therefore, no single flow can exceed the speed of a physical port. However, some PagP-enabled switches can negotiate between a "maximize load balancing" and "preserve ordering" link: the former give maximum aggregated bandwidth at the expense of packet ordering, while the latter assures no packet reordering to occur but limit a single transfer to the bandwidth of a single interface.

References

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External links

Cisco Systems documentation
Ethernet Link protocols Cisco Systems Cisco protocols Bonding protocols