Networking Switching Basics

The two terms associated with frames entering or leaving an interface in networking are 'Ingress' (entering the interface) and 'Egress' (exiting the interface).

A switch uses its MAC address table (Content Addressable Memory/CAM table) to make forwarding decisions and determine the egress interface for a frame based on the destination MAC address.

The two-step process used by a switch for frame forwarding involves: 1. Learning - examining the source address, adding the source MAC if not in the table, and resetting the timeout setting if the source is in the table; 2. Forwarding - examining the destination address and forwarding the frame out the specified port if the destination MAC is in the MAC address table, or flooding the frame out all interfaces except the one it was received if the destination MAC is not in the table.

If the destination MAC address is not in the MAC address table, the switch floods the frame out all interfaces except the one it was received on.

The two methods used by switches to make forwarding decisions after receiving a frame are store-and-forward switching and cut-through switching.

Store-and-forward switching involves error checking, where the switch checks the Frame Check Sequence (FCS) for CRC errors, and buffering, where the ingress interface buffers the frame while it checks the FCS.

Cut-through switching is appropriate for switches needing latency to be under 10 microseconds, does not check the FCS, may lead to bandwidth issues if it propagates too many errors, and cannot support ports with differing speeds going from ingress to egress.

A collision domain is an area where collisions can occur in a network. It is important in determining how devices share the available bandwidth.

Switches alleviate network congestion by using the MAC address table and full-duplex to eliminate collisions, and by employing features such as fast port speeds, fast internal switching, large frame buffers, and high port density.

A broadcast domain extends across all Layer 1 or Layer 2 devices on a LAN and consists of all devices on the LAN that receive the broadcast traffic.

A layer 3 device, such as a router, can break a broadcast domain by routing traffic between different subnets, thereby limiting the scope of broadcast traffic.

Full-duplex operation eliminates collision domains, as it allows for simultaneous data transmission and reception on a communication link.

Auto-negotiation is used as the default setting for duplex and speed in most network devices, including Cisco and Microsoft, to automatically determine and configure the optimal communication parameters between connected devices.

It is important for switches to check the FCS for CRC errors to ensure the integrity of the received frames and to discard any bad frames with errors.

Potential drawbacks of cut-through switching include the inability to check the FCS, which can lead to error propagation, and the limitation in supporting ports with differing speeds going from ingress to egress.

Features of switches that help alleviate network congestion include protocol function, fast port speeds, fast internal switching, large frame buffers, and high port density.