SOHO Networks

how home network routers work

Every home has a SOHO router provided by an ISP that links the LAN to the WAN.

Physical Layer Functions

The router provides Layer 1 functions, such as

a set of RJ45 ports for a local cabled network
a set of radio antennae for receiving wireless signals
a separate port for connecting to the ISP's network
- RJ45 for Ethernet technology
- RJ11 for Digital-Subscriber-Line connections
- F-connector for cable service connections

Data Link Layer Functions

The router provides Layer 2 functions, such as:

an internal Ethernet switch that connects the RJ45
a wireless access point that implements some 802.11 (Wi-Fi) standard.

Remember, each node is addressed at this layer by their MAC-Address.

Network Layer Functions

The router provides Layer 3 functions, which includes packet filtering and forwarding between the public Internet and the private local network. Every node connected via Ethernet cable or wireless link to the local network is assigned an IP address by the router, which runs a DHCP server to automatically and dynamically assign them.

Local IP addresses are usually assigned in the same range as the router, matching the first three octets of the router's address and having the last octet used to identify other nodes.

Forwarding to and from the public Internet uses the router's ISP assigned public IP address.

Security Functions

There isn't an OSI layer for security-related functions, since exploits can arise at any layer of the OSI network and patches are created at all layers. For local networks, all traffic passes through the router. Security rules are implemented using the firewall function provided by the router's manufacturer, like restricting access to a certain website or domain.

All those settings are provided in the router's management interface, and access to that interface is locked behind an administrative passphrase. The default passphrase is weak, and network administrators should always remember to change it when setting up a SOHO network.