Router-on-a-Stick (ROAS) Configuration Lecture

Vocabulary flashcards covering Router-on-a-Stick (ROAS) concepts, including VLANs, trunking, sub-interfaces, and NAT configuration based on the Cisco Networking lecture.

VLAN (Virtual LAN)

A technology that logically separates devices on the same physical switch into different broadcast domains, such as Staff ($VLAN\ 10$) or Students ($VLAN\ 20$).

Layer 2

The layer at which switches operate using MAC addresses; it can forward traffic within a VLAN but cannot move traffic between different VLANs.

Layer 3

The routing layer required to move traffic between two different VLANs or to reach the Internet.

Router-on-a-Stick (ROAS)

A configuration where a single physical router interface handles routing for multiple VLANs using a trunk link to a switch.

Sub-interface

A logical division of a physical router interface (e.g., $G0/0.10$ or $G0/0.20$) where each division acts as the default gateway for one specific VLAN.

802.1Q Trunking

A protocol where the switch tags each frame with a VLAN ID, allowing the router to read the tag and determine which VLAN the frame belongs to.

Access Port

A switch port assigned to exactly one VLAN used to connect end devices like PCs.

Trunk Port

A switch port configured to carry traffic for multiple VLANs simultaneously, identifying each by a tag in the Ethernet frame.

NAT (Network Address Translation)

A process that translates private IP addresses ($192.168.x.x$) to public IP addresses to allow devices to reach the public Internet.

Overload (PAT)

Port Address Translation; a NAT feature that lets many private hosts share a single public IP address using different port numbers.

ip nat inside

A command applied to LAN-facing sub-interfaces where private VLAN traffic originates.

ip nat outside

A command applied to the WAN-facing interface (e.g., $G0/1$) connected toward the ISP/Internet.

Default Route

A routing table entry configured as $ip\ route\ 0.0.0.0\ 0.0.0.0$ that sends all traffic not matching known networks toward the ISP.

ip dhcp excluded-address

A command used to prevent the router from assigning specific addresses (like gateway IPs) from a DHCP pool to hosts.

show vlan brief

A verification command that confirms VLANs exist on the switch and identifies which ports belong to each VLAN.

show interfaces trunk

A verification command that confirms the trunk port is active and allowing the correct VLANs.

show ip interface brief

A command used to confirm that sub-interfaces are status "up/up" and reflect the correct IP addresses.

show ip nat translations

A command that display current mappings of private IP addresses to public IPs and port numbers.

Straight-through (Copper) Cable

The cable type used for connecting a PC to a switch or a switch to a router.

encapsulation dot1Q

The router sub-interface command used to define which VLAN tag the sub-interface is responsible for routing.