Port aggregation protocol

Details Port aggregation protocol Port aggregation protocol

2000-09-19

2001-10-02

Olms, Douglas (Department: 2661)

Multiplex communications

Pathfinding or routing

Switching a message which includes an address header

C370S401000, C370S216000

Reexamination Certificate

active

06298061

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to computer networks and, more specifically, to a protocol for aggregating redundant links in a computer network.
BACKGROUND OF THE INVENTION
Many organizations, including businesses, governments and educational institutions, utilize computer networks so that employees and others may share and exchange information and/or resources. A computer network typically comprises a plurality of entities interconnected by means of one or more communications media. An entity may consist of any device, such as a computer, that “sources” (i.e., transmits) or “sinks” (i.e., receives) data frames over the communications media. A common type of computer network is a local area network (“LAN”) which typically refers to a privately owned network within a single building or campus. LANs typically employ a data communication protocol (LAN standard), such as Ethernet, FDDI or token ring, that defines the functions performed by data link and physical layers of a communications architecture (i.e., a protocol stack). In many instances, several LANs may be interconnected by point-to-point links, microwave transceivers, satellite hook-ups, etc. to form a wide area network (“WAN”) or subnet that may span an entire country or continent.
One or more intermediate devices is often used to couple LANs together and allow the corresponding entities to exchange information. For example, a switch may be utilized to provide a “switching” function for transferring information, such as data frames, among entities of a computer network. Typically, the switch is a computer and includes a plurality of ports that couple the switch to the other entities. The switching function includes receiving data at a source port from an entity and transferring that data to at least one destination port for receipt by another entity.
Another network device is referred to as a router. A router is typically used to interconnect LANs executing different LAN standards and/or to provide higher network functionality, such as efficient message routing. To perform these tasks, a router, which is also often a computer, typically examines and may modify the destination address and source address of all packets passing through the router. Routers typically operate at the network layer of the protocol stack, such as the Internet Protocol of the Transmission Control Protocol/Internet Protocol (“TCP/IP”) reference model. If the LAN standards associated with the source entity and the destination entity are dissimilar (e.g., Ethernet versus Token Ring), the router may alter the format of the packet so that it conforms with the standard corresponding to the destination entity.
FIG. 1
illustrates a conventional computer network
100
comprising a plurality of local area networks (LANs)
101
-
108
that are interconnected by a plurality of switches
111
-
118
and routers
121
-
123
. More specifically, each LAN
101
-
108
is preferably coupled to at least one port
124
of switches
111
-
118
. One or more entities (not shown) for sourcing or sinking data frames are preferably coupled to each LAN
101
-
108
. The switches
111
-
118
and routers
121
-
123
are interconnected by a series of links
126
, such as point-to-point links. Links
126
also couple to ports
124
of the switches
111
-
118
and routers
121
-
123
. Each switch
111
-
118
and router
121
-
123
, moreover, may individually identify its ports, e.g., by numbers one, two, three, etc. Accordingly, each switch
111
-
118
and router
121
-
123
may associate a given port with the particular LAN, switch or router coupled thereto. For example, switch
111
may associate its port number one with LAN
101
, port numbers two and three with router
121
, port number four with switch
112
and port number five with LAN
102
.
The network
100
may also include devices for providing services to the entities. For example, network
100
preferably includes a file server
128
. The file server
128
may be connected to router
121
by two links
126
. Separate ports
124
(e.g., port numbers one and two) at the file server
128
may be associated with each of the links
126
. Thus, data frames may be forwarded by router
121
over either link
126
for receipt by the file server
128
.
Like most computer networks, network
100
includes redundant communications paths so that a failure of any given link does not isolate any portion of the network
100
. For example, switch
111
is connected to router
121
by two links
126
. Thus, in the event one of these links
126
fails, communication between switch
111
and router
121
may continue through the other link
126
. Similarly, routers
122
and
123
are interconnected by multiple links
126
as are router
121
and the file server
128
. The existence of redundant links, however, can introduce significant problems in the network
100
.
For example, file server
128
may have a different address associated with each of its ports
124
, i.e., port numbers one and two. These addresses are used by entities on LANs
101
-
108
when communicating with the file server
128
, e.g., requesting services. The entities, however, may not be aware of both addresses. That is, entities located on LANs
103
and
104
may only be aware of the address of the file server
128
that corresponds to its port number one whereas, entities on LANs
101
and
102
may only be aware of the file server
128
through its address corresponding to port number two. Accordingly, if one of the links
126
that connects the file server
128
with router
121
were to fail, certain entities may be unable to access the file server
128
. For example, if the link
126
associated with port number one of the file server
128
were to fail, entities on LANs
103
and
104
would no longer be able to communicate with the file server
128
, even though the adjacent link between the file server
128
and router
121
(i.e., the link coupled to port number two of the file server
128
) is still functioning. That is, messages addressed to port number one of the file server
128
(which is the only address known by entities on LANs
103
and
104
) cannot be delivered by router
121
, due to the failure of the link corresponding to that port.
One solution to this problem is for router
121
to inform entities on LANs
103
and
104
to address the file server
128
at its port number two following a link failure. This requires router
121
to constantly monitor the availability of both links
126
coupled to the file server
128
. In addition, the router
121
must transmit access messages to each entity on LANs
103
and
104
in the event of a failure of the link. This activity consumes substantial system resources. In addition, some amount of time is required for the access messages from router
121
to reach the entities on LANs
103
and
104
, during which time messages addressed to the file server
128
via port number one may still be lost.
The existence of redundant links may also cause the formation of circuitous paths or “loops” within the network
100
. Loops are highly undesirable because data frames may traverse the loops indefinitely. Furthermore, as a frame travels along a loop, some devices, such as switches
111
-
118
, may become so “confused” as to the location of the entity sourcing the frame as to actually proliferate these “looping” data frames. That is, switches
111
-
118
may create additional copies of these looping frames. The resulting traffic may effectively “shut-down” the network
100
. Intermediate devices, such as routers
121
-
123
, that operate at higher hierarchical layers (e.g., the network layer) within the protocol stack, deliver data frames and learn the addresses of entities on the network differently than switches
111
-
118
, such that routers are generally not susceptible to sustained looping problems.
To avoid the formation of loops, intermediate devices, such as switches, within each segment of the network execute what is known as a spanning tree algorithm. This algorithm

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