Network Devices and Concepts

Network Devices

• Key network devices:

  • Routers

  • Switches

  • Hubs

  • Bridges

  • Servers

  • Access Points

  • Firewalls

  • Wireless LAN Controllers (WLCs)

Hubs

• A hardware device available in 4-port and 8-port variants.

• An obsolete device no longer widely used.

• Functions on the principle of forwarding.

• Forwards incoming packets from one port to all other ports.

• If PC1 wants to communicate with PC8 via a hub, the packet is forwarded to all ports, even though it's intended only for PC8. The other PCs discard the packet.

• Analogy: a postman knocking on every door to find Mr. Sharma, creating unnecessary traffic.

• Generates a lot of traffic, leading to slower network speeds, packet collision and delays.

• Collision Domain:

  • A hub has one collision domain.

  • All devices connected to the hub share a single path for sending and receiving packets.

  • This increases the chance of packet collision when multiple devices transmit simultaneously.

Bridges

• An obsolete device, slightly better than a hub.

• Operates on the principle of filtration.

• Typically a two-port device.

• How it works:

  • The bridge maintains a table that maps devices to its ports (e.g., PC1, PC2, PC3 are on port E0, and PC4, PC5, PC6 are on port E1).

  • If PC1 wants to communicate with PC6, the bridge filters the traffic and forwards the packet only to port E1, where PC6 is located.

  • This reduces unnecessary traffic compared to a hub.

• Collision Domains:

  • A bridge provides two collision domains, one for each port.

  • This reduces the likelihood of collisions compared to a hub.

• Limitations:

  • Adding too many devices can cause the bridge to behave like a hub, leading to increased traffic and collisions.

Switches

• A multiport device that is more intelligent than hubs and bridges.

• Number of ports equals the number of collision domains.

• Combines the principles of forwarding (from hubs) and filtration (from bridges).

• Operates on the principle of unicasting (one-to-one communication).

• Variants: available with 8, 12, 24, 48 ports, etc.

• Unicasting:

  • When PC1 wants to communicate with PC8 via a switch, the switch forwards the packet directly to PC8 without sending it to all other ports.

  • This ensures there is no collision, reliable, and speedy packet delivery.

• MAC Table:

  • The switch builds a MAC table to keep track of which device (identified by its MAC address) is connected to each port.

  • MAC addresses are unique hardware addresses.

    • Analogy: MAC address is like engine/chassis number (permanent), while IP Address is like number plate(can be changed).

  • When a packet enters the switch, it checks the source and destination MAC addresses.

  • Initially, the switch may flood the network to learn the location of devices, adding entries to its MAC table. Flooding will be limited to only the vacant port.

  • Once the MAC table is populated, the switch performs unicasting by forwarding packets only to the port associated with the destination MAC address.

• Collision Domains:

  • Every port on a switch has its own collision domain.

  • This significantly reduces the chance of collisions.

Broadcast Domains

• Hubs, bridges, and switches do not break broadcast domains.

A broadcast domain is essentially a group of devices that can all receive the same broadcast messages. If one device sends out a broadcast, every other device in the same broadcast domain will receive it.

• Problem:

  • In a broadcast, a packet is forwarded to every device on the network, potentially causing a broadcast storm.

  • Broadcast storm: Broadcast storm occurs when network systems flood broadcast messages across the network, eventually causing the network to become completely overloaded.

• Scenario:

  • In a company with multiple buildings, each with a switch and department (HR, Accounts, Sales), a sales manager sends a broadcast message (invitation to a party) intended only for their team.

  • The switches forward the message to all devices across all departments, leading to the entire company being invited.

• Solution: Routers needed to break and isolate broadcast domains.

Routers

• Routers can break broadcast domains.

• The number of ports on a router equals the number of broadcast domains it can create.

• Solution to the broadcast problem:

  • By connecting each department's switch to a different port on the router, the broadcast domain can be limited to that department.

  • If the sales manager sends a broadcast message, the router will not forward it to the other departments (HR, Accounts).

• Key Points Recap:

  • Hub: one collision domain, one broadcast domain.

  • Bridge: two collision domains, one broadcast domain.

  • Switch: Number of ports equals number of collision domains, one broadcast domain.

  • Router: Device that breaks broadcast domains; number of ports equals number of broadcast domains.