CCNA Course Notes

The course begins with foundational network concepts, focusing on IP addressing and subnetting. Initial configuration involves assigning IPv4 addresses to a Layer 3 switch, utilizing private IP address ranges to segment the network. This process establishes a basic network topology and prepares for more complex routing scenarios.

• Choosing a Layer 2 switch for inter-VLAN routing; a Layer 2 switch forwards frames inside VLANs, while a Layer 3 switch can route between VLANs.

• Inter-VLAN routing inside a switch points to a Layer 3 switch.

Applied CCNA troubleshooting often starts at the host. Commands that list interfaces, addresses, gateways, and local routes help verify whether the endpoint can reach the correct next hop before blaming the switch or router. A host routing table command such as `netstat -r` is useful when the default route, on-link network, or more specific route may be sending traffic the wrong way.

• Reading unknown unicast flooding as a routing-table problem; it is a switch MAC table behavior inside a VLAN.

• `netstat -r` is a host route-table clue.

VLAN questions usually ask whether a port carries one VLAN or multiple VLANs. An access port belongs to a single VLAN and is used for end devices such as PCs, printers, or access points in a single client VLAN. A trunk port carries tagged traffic for multiple VLANs between switches, routers, or virtualization hosts, and the allowed VLAN list controls which VLANs are permitted across that link.

• Putting an end-user PC on a trunk when the scenario expects a single VLAN access port.

• Access port means one VLAN; trunk means multiple VLANs with tagging.

Routing-table questions usually test the order of route selection. A router first looks for the most specific matching prefix, so a host route beats a subnet route and a subnet route beats a default route. If two routes have the same prefix length, administrative distance helps decide which source of routing information is trusted more.

• Choosing the route with the lowest administrative distance before checking longest prefix match; the most specific prefix wins first.

• Longest prefix match happens before administrative distance comparison.

DHCP questions focus on how clients receive addressing information without manual configuration. A DHCP scope supplies usable addresses, default gateway, lease information, and options such as DNS servers. DHCP relay matters when the client and server are on different subnets and the router must forward the broadcast-based request toward the server.

• Using DNS to solve address translation; DNS resolves names, while NAT translates addresses.

• DHCP Option 6 is the DNS server option.

CCNA security starts with basic controls before packet filtering. Physical security, locked network rooms, restricted console access, strong passwords, and security awareness reduce the chance that an attacker or careless user reaches the device in the first place. MFA strengthens login security by requiring more than one proof of identity.

• Using a standard ACL when the scenario must match destination, protocol, or port; standard ACLs match source only.

• Standard ACL equals source IP only; extended ACL can match source, destination, protocol, and ports.

Controller-based networking moves policy and management decisions into a centralized controller while forwarding still happens on network devices. The controller can push consistent configuration, collect telemetry, and apply policy dynamically, which reduces manual device-by-device changes in larger environments.

• Confusing underlay and overlay; the underlay provides transport, while the overlay is the logical network built on top.

• Controller-based networking centralizes policy and management decisions.