Redundant topologies
Encyclopedia
A goal of redundant topologies is to eliminate network
downtime
caused by a single point of failure
. All networks need redundancy
for enhanced reliability. Network reliability is achieved through reliable equipment and network designs that are tolerant to failures and faults. Networks should be designed to reconverge rapidly so that the fault is bypassed.
In a redundant mesh topology network devices are connected with many redundant interconnections between network nodes. In a true mesh topology every node has a connection to every other node in the network. A mesh network with redundant connections is an example of a redundant topology. The level of redundancy can be measured by network connectivity
.
On a redundantly connected network if a router were to fail connectivity would be preserved by routing traffic through a redundant connection. Furthermore, each router should have two or more points, or 'legs', with which to keep redundancy.
(time to live) value. If a frame is sent into a layer 2 looped topology of switches, it would loop forever causing serious overhead on the bandwidth of the network.
. The STP
applies a specific algorithm to the network based on its topology with the result of a loop free logical topology .
Network
-Mathematics:* Graph * Complex network* Structure* Flow network-Electric, electronic, biological, and biosocial: * Electrical network* Computer network* Biological network* Artificial neural network* Social network...
downtime
Downtime
The term downtime is used to refer to periods when a system is unavailable.Downtime or outage duration refers to a period of time that a system fails to provide or perform its primary function...
caused by a single point of failure
Single point of failure
A single point of failure is a part of a system that, if it fails, will stop the entire system from working. They are undesirable in any system with a goal of high availability or reliability, be it a business practice, software application, or other industrial system.-Overview:Systems can be made...
. All networks need redundancy
Redundancy
Redundancy may refer to:* Redundancy * Redundancy * Redundancy * Redundancy * Redundancy * Data redundancy* Gene redundancy* Logic redundancy...
for enhanced reliability. Network reliability is achieved through reliable equipment and network designs that are tolerant to failures and faults. Networks should be designed to reconverge rapidly so that the fault is bypassed.
In a redundant mesh topology network devices are connected with many redundant interconnections between network nodes. In a true mesh topology every node has a connection to every other node in the network. A mesh network with redundant connections is an example of a redundant topology. The level of redundancy can be measured by network connectivity
Connectivity (graph theory)
In mathematics and computer science, connectivity is one of the basic concepts of graph theory: it asks for the minimum number of elements which need to be removed to disconnect the remaining nodes from each other. It is closely related to the theory of network flow problems...
.
On a redundantly connected network if a router were to fail connectivity would be preserved by routing traffic through a redundant connection. Furthermore, each router should have two or more points, or 'legs', with which to keep redundancy.
Failures within the Solution
Redundant network topologies are designed to ensure that networks continue to function in the presence of single points of failure. Work is interrupted less often for users because the network continues to function. Any interruptions that are caused by a failure should be as short as possible. Reliability is increased by redundancy. A network that is based on switches or bridges will introduce redundant links between those switches or bridges to overcome the failure of a single link. These connections introduce physical loops into the network. These bridging loops are created so if one link fails another can take over the function of forwarding traffic. In this transition, any unknown destination for currently flowing traffic is flooded over every port except the one it originated from. At layer 2, headers don't have a TTLTime to live
Time to live is a mechanism that limits the lifespan of data in a computer or network. TTL may be implemented as a counter or timestamp attached to or embedded in the data. Once the prescribed event count or timespan has elapsed, data is discarded. In computer networking, TTL prevents a data...
(time to live) value. If a frame is sent into a layer 2 looped topology of switches, it would loop forever causing serious overhead on the bandwidth of the network.
Fix for the Failure
The ultimate solution is to allow physical loops, but create a loop free logical topology. This can be achieved by using the Spanning tree protocolSpanning tree protocol
The Spanning Tree Protocol is a network protocol that ensures a loop-free topology for any bridged Ethernet local area network. The basic function of STP is to prevent bridge loops and ensuing broadcast radiation...
. The STP
Spanning tree protocol
The Spanning Tree Protocol is a network protocol that ensures a loop-free topology for any bridged Ethernet local area network. The basic function of STP is to prevent bridge loops and ensuing broadcast radiation...
applies a specific algorithm to the network based on its topology with the result of a loop free logical topology .