You probably use a router every day to connect your devices to the internet, but do you know how it works? A router is a device that routes data packets between different networks, such as your home network and the wider internet. In this article, you will learn about the main functions and components of a router, how it processes and forwards packets, and how it handles security and performance issues.
A router has three main functions: routing, switching, and filtering. Routing is the process of finding the best path for a packet to reach its destination network. Switching is the process of moving packets from one interface to another within the router. Filtering is the process of applying rules to packets based on their source, destination, or content, and deciding whether to allow or deny them.
Besides enabling local endpoints to communicate in a LAN, a router is a device that allows two separate networks to communicate. Two routers communicating with one another is the most basic manifestation of something you can call "internet."
A router controls traffic in between more than one network to the other. It transmits packages from one endpoint to another over a network. More of like a "traffic cop".
a router connects devices within a network by forwarding data packets between them. This data can be sent between devices, or from devices to the internet. The router does this by assigning a local IP address to each of the devices on the network.
A router has four main components: the CPU, the memory, the interfaces, and the routing table. The CPU is the brain of the router that executes the routing software and processes the packets. The memory is where the router stores information such as the routing table, the configuration, and the packet buffers. The interfaces are the physical or logical connections that link the router to other devices or networks. The routing table is a database that contains information about the available routes to different networks and their costs.
"Routing table poisoning" is a type of attack where a malicious actor makes changes to the routing table database, causing traffic to be redirected. This could be done to evade security detection mechanisms, or to perform a man-in-the-middle attack.
A router has quite a good number of components, for instance the Processor which controls the entire execution of the traffic transmission, the lights which indicate the state of the router, a power button for switching on and off, a reset button to reset the routers configurations, Antennas, Ports and storage spaces.
When a router receives a packet from an interface, it performs several steps to process it. First, it checks the header of the packet to determine its protocol, source, and destination addresses. Second, it looks up the routing table to find the best route for the packet. Third, it modifies the packet header to update the hop count, checksum, and other fields. Fourth, it sends the packet to the appropriate interface based on the routing table entry.
Packet processing in a router involves a series of steps when it gets a packet from a connection. Initially, it examines the packet's header to figure out its protocol, where it comes from, and where it's supposed to go. Next, the router consults its routing table to discover the best path for the packet. After that, it adjusts the packet's header, updating things like the hop count and checksum. Finally, it directs the packet to the right connection according to the information in the routing table.
The routing table is used to decide which network interface to forward a packet to per destination address. To build up the routing table, routers need to run a routing protocol to build up knowledge of the topology of the network or the Internet. Within an AS, a distance vector routing protocol (e.g. RIP) or link state routing protocol (e.g. OSPF) is used. In the former, each router shares its whole routing table to its neighbors only while the latter shares the best next hop to all routers for them to construct their routing table. Link state routing protocols usually converge faster but have larger communication overheads. For inter-AS, a path-vector routing protocol (e.g. BGP) is used. A complete path to destination is usually stored.
When a router forwards a packet to another network, it uses one of two methods: static routing or dynamic routing. Static routing is when the router uses predefined routes that are manually configured by the administrator. Dynamic routing is when the router uses protocols that automatically exchange routing information with other routers and update the routing table accordingly. Static routing is simpler and more reliable, but dynamic routing is more flexible and adaptable to network changes.
Static routing is perhaps simpler to implement, but it can be complex to manage. Every new router you introduce is going to exponentially increase the complexity of your network. Eventually you reach a point where static routing becomes untenable.
Packet forwarding is a crucial aspect of how routers handle data on the internet. When a router receives a packet, which is like a digital envelope containing information, it engages in a process known as packet forwarding. This involves making decisions on how to efficiently send the packet to its intended destination. Upon receiving the packet, the router examines the information in its header, which includes details like the source and destination addresses. Using this information, the router determines the best path for the packet through a process called routing. It consults a routing table, essentially a guide that helps the router decide which path to take based on the destination address.
A router can also provide security features to protect the network from unauthorized access or attacks. Some of these features are: firewall, NAT, VPN, and encryption. Firewall is a feature that filters packets based on predefined rules and blocks unwanted or malicious traffic. NAT is a feature that translates private IP addresses to public IP addresses and vice versa, and allows multiple devices to share a single internet connection. VPN is a feature that creates a secure tunnel between two networks over the internet and encrypts the data. Encryption is a feature that scrambles the data to make it unreadable by anyone who intercepts it.
One fundamental aspect of router security is setting strong, unique passwords for router access. This prevents unauthorized individuals from entering the router's settings and making malicious changes. Regularly updating these passwords enhances security further. Enabling encryption, such as WPA3 for Wi-Fi routers, ensures that the data transmitted wirelessly is protected from eavesdropping and unauthorized access. Disabling unnecessary features and services also reduces the potential attack surface, minimizing vulnerabilities. Frequent router firmware updates are crucial for addressing known vulnerabilities and enhancing overall security.
When using a firewall, logging features and timestamps may also be mentioned in accordance with information security and laws.
When designing your network, consider where your security devices will have the greatest impact. Which side of the router is the IDS/IPS reading traffic from? Examining inbound traffic will alert you to the kinds of threats that are being targeted at your network. However, examining outbound traffic will alert you to the kinds of threats already inside the network.
A router can also affect the performance of the network by influencing factors such as speed, latency, bandwidth, and reliability. Speed is the rate at which data is transferred over the network. Latency is the delay between sending and receiving data. Bandwidth is the amount of data that can be transferred over the network at a given time. Reliability is the ability of the network to deliver data without errors or interruptions. A router can improve the performance of the network by using techniques such as load balancing, caching, compression, and quality of service.