What is the difference between a networks physical topology and its logical topology?

Difference between Physical and Logical Topology

1. Physical Topology :
Physical topology indicates arrangement of different elements of a network. It reflects physical layout of devices and cables to a form a connected network. It is concerned with essentials of network ignoring minute details like transfer of data and device type. The pattern of arrangement of nodes (computers) and network cables depends on ease of installation and setup of the network. It affects cost and bandwidth capacity based on solution of devices. It takes into account placement of nodes and distance between them. Devices can be arranged to form a ring (Ring Topology) or linearly connected in a line called Bus Topology.

2. Logical Topology :
Logical Topology reflects arrangement of devices and their communication. It is the transmission of data over physical topology. It is independent of physical topology, irrespective of arrangements of nodes. It is concerned with intricate details of network like type of devices (switches, routers) chosen and their quality, which affect rate and speed of data packets delivery. The logical topology ensures optimal flow control that can be regulated within network.
The data can either flow in a linear pattern called Logical bus or in form of a circle Logical ring.

Difference between Physical and Logical Topology :

Article Tags :

Computer Networks

Difference Between

Practice Tags :

Computer Networks

Read Full Article

Content: Physical Topology Vs Logical Topology

1. 1. 1. Comparison Chart
      2. Definition
      3. Key Differences
      4. Conclusion

Comparison Chart

Definition of Physical Topology

Physical topology can be considered as a layout of the network media that shows the interconnections of the devices on the network. It specifies which geometric shape the linked devices form with each other. The physical topology does not give much comprehensive detail about the type of devices, the mechanism used for interacting with other devices in the network, and how data is transferred from one device to another.

Therefore, it gives essential details of the network and network devices broadly, neglecting the higher level details like device type, addressing schemes, connectivity, and so on.

The factors that affect communication of devices on a network based on the physical topology selected are:

• Cost
• Scalability
• Bandwidth capacity
• Ease of installation
• Ease of troubleshooting

Types of Physical Topology

Some commonly used physical topologies are the bus, ring and star.

1. Bus topology – Comprised of a single main cable, with which all the devices or pc’s are connected. There is a terminator attached with the cable, in the end, to absorb the signals when it reaches the end of the line.
2. Ring topology – This topology connects all the devices of the network by forming a ring and the flow of data will always be in one direction. It does not require any termination of the cable, as a result, each device has an equal opportunity to access the media. There are two types of ring topology – single ring and dual ring.
3. Star topology – In this topology, all the devices are linked to a central hub by its own cable.
4. Mesh topology – This topology link each device with every other devices in the network.

Definition of Logical Topology

Unlike physical topology, the logical topology emphasis on the manner in which data is transmitted between network nodes instead of the physical layout of the path that data follows. An important fact regarding these topologies is that both physical and logical topologies are independent regarding a network, whether it is of any shape and size.

As a logical topology is a signal path that passes through a physical topology. It handles the –

• Line discipline
• Ordered delivery of frames
• Error notifications
• Optimal flow control.

Types of Logical Topology

1. Logical Bus – The data follows a linear pattern from the source to all destinations.
2. Logical Ring – In this topology, the data travels in the form of a ring from a device to another and reaches to the beginning of the circle.

Difference between physical topology and logical topology

A physical network topology diagram shows the structure of how devices are connected physically inside a network. A logical network topology diagram shows the logical method of communication used by the devices inside the network for network communication. Physical topology specifies the layout how devices are physically connected in the network. Instead, logical topology specifies the manner in which data travels between devices in the network.

Physical topology shows how a network looks physically, but logical topology shows the fashion in which data is circulated inside the network.

About the Author

Andrea Mauro has more than 18 years of IT experience both in SMB and in enterprise scenarios. He is a virtualization, cloud and storage architect, specializing in related VMware solutions and products...

What is a Network Topology?

Network topology is the arrangement of the different network elements of a communication network, usually represented with a graph.

Network topology is an application of graph theory in which different network devices are modeled as nodes and the connections between the devices are modeled as links or lines between the nodes.

There are usually two different types of network topologies:

• Physical network topologyis the placement of the various components of a network and the different connectors usually represent the physical network cables, and the nodes represents usually the physical network devices (like switches).
• Logical network topologyillustrates, at a higher level, how data flows within a network.

Usually, in campus LAN topologies, focusing at layer 2 (at the switching layer), some kind of a structured, multi-tier models are used to simplify the design and the network implementation.

The hierarchical internetworking modelis a three-layer network topology that divides enterprise networks into three layers:

• Core, composed by the highest-speed switches, with high resiliency and usually routing and other high-level functions.
• Distribution or aggregation, composed by high-speed switches with redundancy and availability.
• Access, composed of switches to which the client devices are connected.

There are also other models, for example a simplified two-layer model (with only core and access layers, mostly used in the SMB segment) or also other new types of models like the leaf-spine model, which focuses more on cloud computing or data center environments.

Anyway, the terms core, distribution/aggregation and access are so commonly used, that the switches are usually classified for their intended purpose. For example see the Aruba Switch portfolio.

Let’s consider a common logical topology of a three-layer model:

Three-layer hierarchical layer 2 topology

Potentially this can be directly translated in a physical topology, will be a totally non-redundant solution, where each node is just a single switch and the switches in each layer have a single link to switches in the adjacent layers.

Non-redundant 3-tier LAN

Seems a very weak solution, doesn’t it? It could be, but switches in each layer can have internal redundancy, such as redundant management, fabric and power. This can provide a reasonable amount of redundancy. For example, the core node could be a modular switch (like the Aruba 8400 model.) https://www.arubanetworks.com/products/networking/switches/8400-series/

Also, more physical links can be used and aggregated in link aggregation (LAG or LACP logical link) to improve resiliency and bandwidth.

But usually the physical topology is designed to have full redundancy at core and aggregation level to provide full redundancy and fault tolerance:

Redundant core and aggregation layer

This model is widely used because of its resiliency, but can it also provide more performance and bandwidth? Having multiple links and paths does not necessarily mean more throughput!

At least it does not on a layer 2 network, because of the limitation of the IEEE 802.3 family (the standard version of Ethernet protocols) where no loop is supported due to the lack of a layer 2 Time to Live (TTL).

This means that the real physical topology must become a hierarchical graph with no loop at all.

To achieve this goal there are two main options:

• The first is moving again to a physical topology without redundancy (as in the first diagram) and improve the resiliency using modular switches, or stacking switches or also independent switches in virtual chassis configuration. Note that Aruba switches give you all those options depending by the model and the usage (for example the 83xx series support the VSX virtual chassis, the 84xx series is totally modular, and the 38xx series supports stacking).
• The second option is to use the Spanning Tree Protocol (STP) in order to deactivate some physical links, to automatically transform a physical topology with loop and one loop free. This means that the network fabric is not totally used. Some links will be down and in a standby fashion. Also some switches may be not normally used. Using multiple STP (802.1s), one for each different VLAN, could make the infrastructure more utilized, but can be also more complex.

Depending on your switches and your needs, you can choose one option or another.

Usually the first option may be a little more costly, because you need specific stacking modules or you are losing some switch ports or you have to buy modular switches.

But the second option may be more complex from a design perspective, bring possible issues (especially in troubleshooting) and be less efficient.

SMBs usually use a simplified two-layer model and for the core layer use a stacked or modular solution.

Leaf-Spine Network Topology

The leaf-spine topology is a special case of a two-layer model, designed to build fast, predictable, scalable and efficient data center network infrastructure.

The main difference between the previous topology is the spine level, where there are more independent switches that are more scalable. The switches on the spine level are not connected each other:

Leaf-spine network topology

Another big difference is that the leaf-spine topology is natively a layer 3 network that uses layer 3 routing and each node is a router. Usually, all routes are configured in an active state through the use of Equal-Cost Multipath (ECMP) to have all links active.

So, the first big problem with this topology is how stretch layer 2 networks (usually the different VLANs) on a layer 3 network? Network virtualization and protocols like VxLAN can help in this goal.

Another aspect is how match this topology in a physical topology? Can it be done 1:1? Depending on your type of network and level, maybe. In some cases, each leaf node represents a couple of physical switches (usually the top-of-rack switches) configured to be a single logical switch (with stacking or virtual chassis features).

The leaf-spine topology is not really used in the SMB market.

Auto-Discover Network Topologies

There are some tools and protocols that are useful to build your network topology.

In most cases those tools are used in the Wi-Fi network to simplify the deployment and configuration.For example, with AirWave 8.2.4, Aruba introduced the network topology feature, which is a layer 2 map of the wired network.

But there are also some interesting options for the wired LAN.For example, Link Layer Discovery Protocol (LLDP) is a vendor-neutral link layer protocol used by network devices for advertising their identity, capabilities and neighbors on a local area network based on IEEE 802 technology, specifically 802.1AB. This permits automatically discovery and advertising of the node neighbors.

Several tools use this protocol to automatically build the network topology.For example, in Aruba Central, the topology map provides a graphical representation of the network layout, details of the devices deployed in a branch site, and the health of the links.

Read My Other Blogs

Stacking Network Switches: Why and Why Not

Network Security on Modern Switches

Tags:

• Campus Networking
• Campus Switches
• GestaltIT
• Network Design
• Network Infrastructure
• Networking

Here is the difference between Physical and Logical topology.

Table of Contents

• What is Physical Topology? [Definition]
• What is Logical Topology? [Definition]
• Comparison Chart [Pysical Vs Logical Topology]
• Different Types of PhysicalTopology

What is Physical topology?

Asname its name depicts, physical topology mentions the physical design of the network.

What is logical topology?

At the same time, the logical topology indicates how data is managed in the network irrespective of its physical topology.

Physical Vs Logical Topology:

• The potentials of the network access devices and media decides the physical topology of a network.
• In terms of arithmetic, the physical topology of a network is the real arithmetical arrangement of workstations.
• Logical topology shows the temperament of the courses the way signals move from node to node.
• The network administrator configures these topologies at the physical layer of 7 layer OSI model in networking.

What are the different types of physical topology?

Physical topologies are further differentiated into following topologies.

• bus network topology
• point to point topology
• star network topology
• ring network topology
• mesh network topology
• hybrid topology
• tree network topology

In a lot of cases, the logical topology is no different as the physical topology. Many of us getconfused over this point.

The logical topology is the mode that the signals proceed on the network media. It is the approach that the data traverses the network from one apparatus to the next with no regard to the physical interconnection of the devices.

Related read:difference between subnetting andsupernetting.

Hope this discussion on the difference between physical and logical topology helps you to get the things in a better way. If you have any doubt feel free to write in the comment section.

Computer Networknetwork topology