Networking Protocols, VLANs, and Routing Concepts for Cisco

Topic

Definition/Explanation

Dynamic Routing

Automated routing where routers share information via protocols to update routing tables.

Convergence

The time it takes for all routers in a network to agree on the network topology.

Routing Information Protocol (RIP)

A distance-vector protocol that uses hop count as its metric (max 15 hops).

Enhanced IGRP (EIGRP)

Cisco proprietary advanced distance-vector/hybrid protocol with fast convergence.

Open Shortest Path First (OSPF)

A link-state protocol that uses cost as a metric and divides networks into areas.

Distance Vector vs Link State

Distance vector shares routing tables with neighbors; link state shares topology maps with all routers.

Border Gateway Protocol (BGP)

Path-vector protocol used for routing between autonomous systems (the internet).

Edge Router

A router at the boundary of a network that often performs NAT and firewall functions.

Static NAT

One-to-one mapping of a private IP to a public IP.

Port Address Translation (PAT)/NAT Overload

Many private IPs share one public IP using different port numbers.

Access Control List (ACL)

A set of rules that control traffic flow based on IP addresses, ports, or protocols.

IP Filtering

Blocking or allowing traffic based on source/destination IP addresses.

Port Filtering

Blocking or allowing traffic based on TCP/UDP port numbers.

Stateless vs Stateful Firewall

Stateless checks packets individually; stateful tracks connections and context.

Hybrid Types: Hierarchical Star

Combines star topology with hierarchical layers (core, distribution, access).

Hybrid Types: Star-Mesh

Combines star and mesh topologies for redundancy and scalability.

Hybrid Types: Star of Stars

A larger star topology where each node is itself a star network.

3-Tiered Hierarchy

Core layer (speed), distribution layer (policy), access layer (user connectivity).

Trunking

A link that carries multiple VLAN traffic between switches using tagging.

Tagged vs Untagged Ports

Tagged ports carry VLAN tags (trunk); untagged ports do not (access).

VLAN Communication Layer

VLANs communicate at Layer 2 (Data Link) within the same VLAN.

Default VLAN

VLAN 1; all ports belong here unless reconfigured.

Native VLAN

The VLAN that receives untagged traffic on a trunk port (default VLAN 1).

Management VLAN

A dedicated VLAN for managing network devices (e.g., switches, routers).

Voice VLAN

A VLAN prioritized for VoIP traffic to ensure quality.

IEEE 802.1Q

The standard for VLAN tagging on Ethernet frames.

Router on a Stick

A single router interface with subinterfaces routing between VLANs.