The Physical layer handles the actual transmission of raw bits over the medium. It involves cables, connectors, and electrical signals that form the foundation of network communication.

The 'show running-config' command displays the active configuration of the router. It is essential for reviewing settings and troubleshooting configurations.

Routers are designed to connect different networks and determine the best path for data packets. They are critical in directing traffic efficiently across multiple networks.

DHCP (Dynamic Host Configuration Protocol) automatically assigns IP addresses to devices on a network. This automation simplifies address management and reduces configuration errors.

The 'enable' command elevates the user to privileged EXEC mode, granting access to advanced commands. This mode is necessary for performing configuration changes and troubleshooting.

The command 'configure terminal' transitions the device into global configuration mode. This mode is used for setting up and modifying system-wide settings.

VLANs (Virtual Local Area Networks) are used to divide a switch into separate broadcast domains. This segmentation helps reduce unnecessary traffic and enhances security by isolating network segments.

OSPF (Open Shortest Path First) uses a cost metric that is typically based on the link bandwidth. This allows OSPF to determine the most efficient route through a network.

NAT stands for Network Address Translation and is used to convert private IP addresses to a single public IP address. This process aids in both preserving scarce public IP addresses and adding a layer of security.

The Transport layer is charged with end-to-end error recovery and flow control. It ensures that data is reliably transmitted between hosts, managing retransmissions if necessary.

The 'show ip interface brief' command provides a concise overview of all interfaces along with their IP addresses and statuses. This information is vital for quickly identifying connection issues.

RIP (Routing Information Protocol) relies on hop count as its metric and periodically sends its entire routing table to its neighbors. This makes it simple to configure, though less efficient for larger networks.

STP prevents loops in networks that have redundant switch connections by blocking certain paths. This is critical for avoiding broadcast storms and maintaining a stable network topology.

SSH (Secure Shell) encrypts communications, providing a secure method for remote device management. Unlike Telnet, SSH protects sensitive data from being transmitted in plaintext.

The subnet mask is used to distinguish which part of an IP address represents the network and which part represents the host. This separation is crucial for proper routing and network segmentation.

The 'ip route' command is used to add a static route to the routing table, defining a specific next-hop address for traffic. This can direct packets along desired paths when dynamic routing is not suitable.

LACP (Link Aggregation Control Protocol) automatically negotiates and manages the bundling of multiple physical links into a single EtherChannel. This enhances bandwidth and provides redundancy in network connections.

The 'show ip ospf neighbor' command is used to display the status and details of OSPF neighbors. This command is invaluable for confirming the establishment of OSPF adjacencies during troubleshooting.

ACLs are used to permit or deny traffic based on specified rules, thereby enhancing network security. They act as filters that control the flow of data into and out of a network.

Implementing NAT helps by hiding internal IP addresses, thereby enhancing security, while VPNs provide encrypted channels for remote access. Together, these features optimize both network security and performance in complex environments.