Network Layer

WAN is a network that covers a broad geographic area, which often uses service providers’ (SP) transmission facilities and operates on Physical Layer#, Data Link Layer# and Network Layer# to connect several #Local-Area Network (LAN). Several network devices could operate within WAN such as Switch# (at data link layer) and Router#.

VPN encrypts# the traffic in Network Layer.

We can apply access rules and provision services to the users of same or similar responsibilities without the need to change the topology of the network or changing the IP Address. Furthermore, VLAN can also create their own Broadcast Domain# without the help from Network Layer Network Device (modern #Switch and #Router). Basically, we could assign the hosts in a subnet# to be in the same VLAN. By using VLAN, we could have different broadcast domains even in a single switch so that broadcast flooding affects only those in the same grouping. If a link needs to handle more than one VLAN, #VLAN Trunking will be used.

Transport Layer is the forth layer in #Open Systems Interconnection (OSI) Model. It has the same name under #Internet Protocol Suite (TCP/IP). Its main purpose is to transfer the chunk of data from Application Layer onto the network. Sometimes, it will cut down the sizes of the data and send them as several packets (its #Protocol Data Units (PDU)). Their header will identify the Well-Known Ports# or socket numbers of the sender and receiver.

Switch is a #Network Device that can operates in either Data Link Layer# or Network Layer# (modern implementation). It is an intelligence Bridge, which provide superior throughput performance, more ports (lower per-port cost), high-speed connections, segmentation using Virtual LAN (VLAN)# or Broadcast Domain# (modern), and even routing (in the case of Multilayer Switch). This makes large-scale segmentation possible within the [Local-Area Network (LAN)](202207051554)❌.

Router is a #Network Device operates at Network Layer# which forwards packets from source to destination based on network layers protocols (reading the source and destination IP Address). It will communicate with other routers using Routing Protocol# (dynamic routing) or be manually edited by network administrators (static routing) to maintain or update their Routing Table# that contain optimal routing paths. Of course Router needs to be connected to a network to establish either dynamic routing or static routing.

OSPF is a #Layer 3 #classless #Link-State Routing Protocol developed by Internet Engineering Task Force (IETF)# where its metric is an arbitrary value called cost (defined by RFC 2328). In Cisco, the cost calculated using bandwidth. It is secure, scalable and provides fast Convergence#. It supports both IPv4 and IPv6. The implementation of OSPF varies from vendor to vendor.

The following devices operate at Network Layer# :

TCP/IP is a #Protocol Suite that is widely used for Internet or other computer networks connection. Internet Protocol (IP)# forms the foundation for it. It also comprises some Application Layer, Transport Layer and Network Layer protocols.

IP is the underlying protocol used by World Wide Web (WWW) to connect other computers over the network which is included in the #Internet Protocol Suite (TCP/IP). It is considered as #Network Layer protocol according to #Open Systems Interconnection (OSI) Model. Currently, it has two versions: IPv4# and IPv6#.

ISDN is a set of technologies developed to carry voice, video and data across Public Switched Telephone Network (PSTN) by existing telephone lines. It utilises #Circuit Switching and primarily operates at Physical Layer#, Data Link Layer# and Network Layer#. ISDN offers bandwidth from 128kbps up to 384kbps. It was the first #broadband service deployed in the home but nowadays, it has been outshone by Digital Subscriber Line (DSL) and Cable Modem.

IPsec is an #Network Layer security framework for secure communications over Internet Protocol (IP)# network. This means it could protect every application or Protocol#, including those that are security-ignorant (doesn’t design around security), running on top of IP (IPv4 or IPv6#, however, both of them are not compatible to each other). It is common having it to have secure access over the Internet, extranet and intranet connectivity with partners or just to enhance the security especially in electronic commerce. It provides Authentication#, Confidentiality#, and key management (secure key exchanges) services.

e2e occurs between the original source and the final destination, that is the encryption is happened in either Application Layer#, Presentation Layer#, Transport Layer# or Network Layer#. This implies that they have the shared keys. e2e only concerns about the encryption of the user data. If user’s privacy and security is desirable, then e2e is preferred. However, due to the translation limit when jumping between different network technology such as IPv4# and IPv6#, the data sent must be decrypted and then be transformed to an understandable form. This could be a huge compromise.

Note: Router and Personal Computer (PC) are considered to be the same kind of end device since they both could operate at Network Layer#.

Broadcast Domain is a network segment where a device can receive all broadcast messages from the members of the segment. It is usually segmented by Network Layer# Network Device# (modern #Switch and #Router).