Module 4_Inter-VLAN Routing

VLANs

are used to segment switched Layer 2 networks for a variety of reasons.

router, Layer 3 switch

Regardless of the reason, hosts in one VLAN cannot communicate with hosts in another VLAN unless there is a _____ or a _____ to provide routing services.

Inter-VLAN routing

is the process of forwarding network traffic from one VLAN to another VLAN.

Legacy Inter-VLAN routing,

Router-on-a-Stick,

Layer 3 switch using switched virtual interfaces (SVIs)

three inter-VLAN routing options

Legacy Inter-VLAN routing

This is a legacy solution. It does not scale well.

Router-on-a-Stick

This is an acceptable solution for a small to medium-sized network.

Layer 3 switch using switched virtual interfaces (SVIs)

This is the most scalable solution for medium to large organizations.

first inter-VLAN routing solution

relied on using a router with multiple Ethernet interfaces

first inter-VLAN routing solution

Each router interface was connected to a switch port in different VLANs.

router interfaces

The ____ served as the default gateways to the local hosts on the VLAN subnet.

Legacy inter-VLAN routing using physical interfaces

It is not reasonably scalable because routers have a limited number of physical interfaces.

physical router interface per VLAN

Requiring one ____ quickly exhausts the physical interface capacity of a router.

Router-on-a-Stick Inter-VLAN Routing

overcomes the limitation of the legacy inter-VLAN routing method.

Router-on-a-Stick Inter-VLAN Routing

It only requires one physical Ethernet interface to route traffic between multiple VLANs on a network.

Cisco IOS router Ethernet interface

is configured as an 802.1Q trunk and connected to a trunk port on a Layer 2 switch.

Specifically, the router interface is configured using subinterfaces to identify routable VLANs.

Router-on-a-Stick Inter-VLAN Routing

The configured subinterfaces are software-based virtual interfaces.

Router-on-a-Stick Inter-VLAN Routing

Each is associated with a single physical Ethernet interface.

Router-on-a-Stick Inter-VLAN Routing

Subinterfaces are configured in software on a router.

Each subinterface is independently configured with an IP address and VLAN assignment

logical routing

Subinterfaces are configured for different subnets that correspond to their VLAN assignment. This facilitates _____.

VLAN subinterface

When VLAN-tagged traffic enters the router interface, it is forwarded to the ____

destination IP network address

After a routing decision is made based on the _____, the router determines the exit interface for the traffic.

data frames

If the exit interface is configured as an 802.1q subinterface, the ____ are VLAN-tagged with the new VLAN and sent back out the physical interface

50 VLANs

The router-on-a-stick method of inter-VLAN routing does not scale beyond ____

Inter-VLAN Routing on a Layer 3 Switch

modern method of performing inter-VLAN routing

switched virtual interfaces (SVI)

is a virtual interface that is configured on a Layer 3 switch

Layer 3 switch

is also called a multilayer switch as it operates at Layer 2 and Layer 3. However, in this course we use the term Layer 3 switch.

Inter-VLAN SVIs

are created the same way that the management VLAN interface is configured.

SVI

is created for a VLAN that exists on the switch.

SVI

Although virtual, _____ performs the same functions for the VLAN as a router interface would.

Layer 3 processing

Specifically, it provides _____ for packets that are sent to or from all switch ports associated with that VLAN.

Layer 3 switches for inter-VLAN routing

advantage:

They are much faster than router-on-a-stick because everything is hardware switched and routed.

Layer 3 switches for inter-VLAN routing

advantage:

There is no need for external links from the switch to the router for routing.

Layer 3 switches for inter-VLAN routing

advantage:

They are not limited to one link because Layer 2 EtherChannels can be used as trunk links between the switches to increase bandwidth.

Layer 3 switches for inter-VLAN routing

advantage:

Latency is much lower because data does not need to leave the switch in order to be routed to a different network.

Layer 3 switches for inter-VLAN routing

advantage:

They more commonly deployed in a campus LAN than routers.

Layer 3 switches for inter-VLAN routing

The only disadvantage is that Layer 3 switches are more expensive.

router-on-a-stick method

requires you to create a subinterface for each VLAN to be routed

interface interface_id subinterface_id

A subinterface is created using the _____ global configuration mode command.

subinterface syntax

is the physical interface followed by a period and a subinterface number

subinterface number

Although not required, it is customary to match the _____ with the VLAN number.

encapsulation dot1q vlan_id [native],

ip address ip-address subnet-mask

Each subinterface is then configured with the following two commands

encapsulation dot1q vlan_id [native]

This command configures the subinterface to respond to 802.1Q encapsulated traffic from the specified vlan-id.

native

_____ keyword option is only appended to set the native VLAN to something other than VLAN 1

ip address ip-address subnet-mask

This command configures the IPv4 address of the subinterface.

ip address ip-address subnet-mask

This address typically serves as the default gateway for the identified VLAN.

router subinterface

Each _____ must be assigned an IP address on a unique subnet for routing to occur.

no shutdown

When all subinterfaces have been created, enable the physical interface using the _____ interface configuration command.

physical interface

If the _____ is disabled, all subinterfaces are disabled.

router-on-a-stick configuration

is complete after the switch trunk and the router subinterfaces have been configured.

show ip route,

show ip interface brief,

show interfaces,

show interfaces trunk

In addition to using ping between devices, the following show commands can be used to verify and troubleshoot the router-on-a-stick configuration. (4)

router-on-a-stick method

is simple to implement for a small to medium-sized organization.

Enterprise campus LANs

____ use Layer 3 switches to provide inter-VLAN routing.

Layer 3 switches

use hardware-based switching to achieve higher-packet processing rates than routers.

Layer 3 switches

are also commonly implemented in enterprise distribution layer wiring closets.

Layer 3 switches

Route from one VLAN to another using multiple switched virtual interfaces (SVIs).

Layer 3 switches

Convert a Layer 2 switchport to a Layer 3 interface (i.e., a routed port).

routed port

is similar to a physical interface on a Cisco IOS router.

interface vlan vlan-id

SVIs are configured using the same _____ command used to create the management SVI on a Layer 2 switch

Layer 3 SVI

must be created for each of the routable VLANs.