Read: Class 04 Routing - VascoLucas01/networking-reading-notes GitHub Wiki
Introduction
In this Read it will me discussed four points:
- Network Topologies
- Routing Technologies
- Dynamic Routing
- Network Switching Overview
Network Topology
A network topology is the physical and logical arrangement of nodes (host or router) and connections in a network.
Aboout Network Topology it will be discussed 7 topologies:
- Star Topology
- Ring Topology
- Bus Topology
- Mesh Topology
- Hybrid Topology
- Wireless Topology
Star Topology
Also known as a spoke and hub configuration, in this setup devices are connected not to one another but rather to a central master/controller or hub. So messages can't be passed from one devide to another directly but must go through the central master/controller.
The most benefit of star topologies is that the failure of one node doesn't impact the rest of the network. It's also simpler to add devices on the network as the only connection is to the central master. On the other hand, the central master is the main point of failure, so if it fails the entire network stops working. Plus, adding devices to the network requires additional cabling, which can get expensive as the device count rises.
Each "spoke" runs a (separate) Ethernet protocol (nodes do not collide with each other).
Ring Topology
Each node in a ring topology connects to exactly two other nodes. This forms a single pathway for signals through each node of the network, which resembles a ring. Messages or frames travel through the entire ring and can theorically be picked up and/or read by any device on the ring.
Among the benefits of ring topologies are the lack of any central controller to manage the messaging between devices. It's also easy to find and isolate a fault on the network and reconfiguring or adding devices is relatively simple. On the downside, more devices on the network can slow transmission speeds and cause delays. It's also more difficult to configure than other network topologies such as a star network.
Bus Topology
In a bus topology, all devices (or nodes) are connected together through a commom link called the bus. Each node on the bus receives all the network traffic.
One of the benefits of bus networks is the ease of connecting devices onto the network, which generally requires less cabling that a star topology, for instance. Also, failure of a node does not impact the rest of the network. On the downside, a network cable failure shuts down the entire network. Also, adding nodes can slow down the network.
Popular through mid 90s. All nodes in same collision domain (can collide with each other).
Mesh Topology
It is another popular topology, especially in larger networks.
Mesh topology is a type of network topology in which all devices in the network are interconnected. The two types of mesh topology are:
- Full mesh topology: Every device in the network is connected to all other devices in the network. A full mesh offers high level of redundancy but is expensive to implement. As such, it's typically used for network backbones.
- Partial mesh topology: Only some of the devices in the network are connected to multiple other devices in the network. A partial mesh is more practical and cost-effective that a full mesh, and is more widely used.
Hybrid Topology
A Hybrid topology is a type of network topology that uses two or more differing network topologies.
Wireless Topology
In this topology, it is possible to communicate in a number of different ways.
If you're using an access point, you're probably communicatiing over an infrastructure connection. This means that all of the devices on your network are communicating through an access point. If you just have two devices and there's no access point, you can connect directly from one device to another device using ad hoc networking - each device can function as both a client and a server, and can forward data to other devices within the network.
Routing Technologies and Dynamic Routing
When we send traffic across the internet, the packet passes through a lot of routers in which each router analyse to know where it should be sent.
First of all, it is important to distinguish two important concepts that generally are misunderstanding.
Routing vs Forwarding
The forwarding process refers to the process of select an exit port based on the destination IP address and on the routing table. The routing process refers to a process of the routing table's creation. Function to find the path in the network.
Indeed, typically a machine or a router does not have information about all the possible destinations. Hosts normally have configured a default gateway where they rely on routers to their routing. Futhermore, the routers know several paths and can also have a route by default (0.0.0.0/0).
However, the router needs to be configured and there are two options:
- Manually configuration
- Dynamic configuration
The manually configuration can be accomplished by static routes.
The dynamic configuration can be accomplished by RIP (Routing Information Protocol), OSPF (Open Shortest Protocol First) or EIGRP (Enhanced Interior Gateway Routing Protocol). Additionally, there are routers on your network that are using dynamic routing protocols to be able to build its routing table. This is not unusual when you might have an internet router where you might be using OSPF on the inside of your network, and BGP on the outside of your network. See the example below.
The figure above shows a topology of different ASes connected. Inside of each AS, each router runs OSPF as IGP (Interior Gateway Protocol) inside the AS and BGP as EGP (EXterior Gateway Protocol), except the RIPv2 domain next to the AS 40 that runs RIPv2 as IGP and BGP as EGP. Following the figure above, let's focus on the backbone area (area 0) of AS 40. Since we are using two different routing protocols, we are going to have completely different types of metrics that help to determine where the next hop might go. And we can't compare the metrics across these different routing protocols, because they use completely algorithms to be able to make these determinations.
Fortunately, there is a tiebreaker. This tiebreaker is an administrative distance. This is used by the router to determine what routing protocol has priority over another.
So, if a route is received by eBGP and OSPF, the route that will be installed in the routing is from eBGP, because 20<110.
Network Switching Overview
Switches are layer 2 (OSI) devices that forward traffic based on layer 2 (MAC) address of the hosts. They need to keep an internal table of the hosts' location that they learned. The switch builds this list by looking at inbound traffic and examining the source MAC address and trying that source MAC address to a specific physical interface.
The figure above shows that the switch's architecture is made up of different levels that allow switching frames between interfaces.
The MAC's entity have a role of receiving and sending packets through the interfaces.
The Relay's entity allows to perform the switching functions of the frames between the interfaces.
The high level's entity is responsable for the management of the switches and the topology's calculation.
The figure below shows the switching process of the switch.
The FDB refered in the figure above stands for Fowarding Database, which is a table maintained by a switch that maps the MAC addresses and related port of network devices. The FDB is used by the switch to determine where to foward incoming frames, based on the destination MAC address.
What is the ARP protocol?
On an IPv4 network, devices are able to obtain the MAC address of a remote device using the ARP protocol. ARP stands for address resolution protocol. ARQ will query the network for a specific IP address, and that IP address will respond back with its MAC address. Your local computer keeps a cache of all the MAC addresses that it currently knows. If you wanted to look at the ARP address table on your local machine, ou can use the command arp -a.
Follow the next example:
In the figure above a Kali Linux host is trying to establish a connection with Windows 10 host through FTP.
Let's see the content of the Address Protocol Resolution Request:
Let's see the content of the Address Protocol Resolution Reply:
After analysing it is important to notice the MAC address of the target host in the ARP request. Since it is not known, it is sent that special MAC address.
REFERENCES
1 - https://www.techtarget.com/searchnetworking/definition/network-topology
3 - https://www.professormesser.com/network-plus/n10-008/n10-008-video/network-topologies-5/
4 - https://www.geeksforgeeks.org/advantage-and-disadvantage-of-mesh-topology/
5 - https://www.sunbirddcim.com/glossary/mesh-topology
7 - https://www.professormesser.com/network-plus/n10-008/n10-008-video/routing-technologies-n10-008/
8 - https://www.examguides.com/CCNP-Route/ccnp-routing-13.htm