Module 4: Inter-VLAN Routing

VLANs

______ are used to segment switched Layer 2 networks for a variety of reasons. Regardless of the reason, hosts in one ______ cannot communicate with hosts in another ______ unless there is a router or a Layer 3 switch 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)

There are 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

The _____________ relied on using a router with multiple Ethernet interfaces. Each router interface was connected to a switch port in different VLANs.

default gateways

The router interfaces served as the ____________ to the local hosts on the VLAN subnet.

Legacy inter-VLAN routing

_________________ using physical interfaces works, but it has a significant limitation. It is not reasonably scalable because routers have a limited number of physical interfaces. Requiring one physical router interface per VLAN quickly exhausts the physical interface capacity of a router

Legacy inter-VLAN routing

This method of inter-VLAN routing is no longer implemented in switched networks and is included for explanation purposes only.

‘router-on-a-stick’ inter-VLAN routing

The ______________________ method overcomes the limitation of the legacy inter-VLAN routing method. It only requires one physical Ethernet interface to route traffic between multiple VLANs on a network.

802.1Q trunk

A Cisco IOS router Ethernet interface is configured as an ___________ and connected to a trunk port on a Layer 2 switch. Specifically, the router interface is configured using subinterfaces to identify routable VLANs.

configured subinterfaces

The _________________ are software-based virtual interfaces. Each is associated with a single physical Ethernet interface

Subinterfaces

____________ are configured in software on a router. Each ___________ is independently configured with an IP address and VLAN assignment.

Subinterfaces

are configured for different subnets that correspond to their VLAN assignment. This facilitates logical routing.

VLAN subinterface

When VLAN-tagged traffic enters the router interface, it is forwarded to the ____________. After a routing decision is made based on the destination IP network address, the router determines the exit interface for the traffic.

50 VLANs

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

• Layer 3 switches

• switched virtual interfaces (SVI)

The modern method of performing inter-VLAN routing is to use ________________ and ______________

SVI

An _____ is a virtual interface that is configured on a Layer 3 switch, as shown in the figure.

multilayer switch

A Layer 3 switch is also called a __________ 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. Although virtual, this performs the same functions for the VLAN as a router interface would.

SVI

it provides Layer 3 processing for packets that are sent to or from all switch ports associated with that VLAN.

three subinterfaces

[Router-on-a-Stick]

To route between VLANs, the R1 GigabitEthernet 0/0/1 interface is logically divided into ?

VLANs and trunking, inter-VLAN routing

[Router-on-a-Stick Scenario]

To enable devices to ping each other, the switches must be configured with __________and ________, and the router must be configured for _____________.

• Step 1. Create and name the VLANs.

• Step 2. Create the management interface.

• Step 3. Configure access ports.

• Step 4. Configure trunking ports.

the following steps to configure S1 with VLANs and trunking:

router-on-a-stick

The _____________ method requires you to create a subinterface for each VLAN to be routed.

subinterface

A ___________ is created using the interface interface_id subinterface_id global configuration mode command.

subinterface syntax

The ______________ is the physical interface followed by a period and a subinterface number. Although not required, it is customary to match the subinterface number with the VLAN number.

• encapsulation dot1q vlan_id [native]

• 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. The native keyword option is only appended to set the native VLAN to something other than VLAN 1

ip-address subnet-mask

This command configures the IPv4 address of the subinterface. This address typically serves as the default gateway for the identified VLAN

IP address

Each router subinterface must be assigned an ___________ 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.

VLANs 10, 20, and 99.

In the configuration, the R1 G0/0/1 subinterfaces are configured for ?

router-on-a-stick configuration

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

hosts, router, and switch.

The configuration can be verified from the _______,_______, and _______

ping command

From a host, verify connectivity to a host in another VLAN using the __________

ipconfig

It is a good idea to first verify the current host IP configuration using the _________ Windows host command.

• 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:

router-on-a-stick

Inter-VLAN routing using the _________ method is simple to implement for a small to medium-sized organization. However, a large enterprise requires a faster, much more scalable method to provide inter-VLAN routing.

Layer 3 switches

Enterprise campus LANs use ___________ to provide inter-VLAN routing.

hardware-based switching

Layer 3 switches use _____________ to achieve higher-packet processing rates than routers.

Layer 3 switches

are also commonly implemented in enterprise distribution layer wiring closets.

SVIs

To provide inter-VLAN routing, Layer 3 switches use _____

interface vlan

SVIs are configured using the same ___________ vlan-id command used to create the management SVI on a Layer 2 switch.

Step 1. Create the VLANs.

Step 2. Create the SVI VLAN interfaces.

Step 3. Configure access ports.

Step 4. Enable IP routing.

the following steps to configure S1 with VLANs and trunking:

default gateway

The IP address configured will serve as the ____________ for hosts in the respective VLAN

ip routing global configuration

Issue the ________________ command to allow traffic to be exchanged between VLANs 10 and 20. This command must be configured to enable inter-VAN routing on a Layer 3 switch for IPv4.

router-on-a stick method

Inter-VLAN routing using a Layer 3 switch is simpler to configure than the ?

static or dynamic routing.

If VLANs are to be reachable by other Layer 3 devices, then they must be advertised using _______ and ___________

routed port

A ___________ is created on a Layer 3 switch by disabling the switchport feature on a Layer 2 port that is connected to another Layer 3 device.

Step 1. Configure the routed port.

Step 2. Enable routing.

Step 3. Configure routing.

Step 4. Verify routing.

Step 5. Verify connectivity

the following steps to configure D1 to route with R1:

no switchport command

Configure the routed port. Use the _____________ to convert the port to a routed port, then assign an IP address and subnet mask. Enable the port.

• show vlan [brief]

• show interfaces switchport

Issue Type: Missing VLANs

how to verify?

• show interface trunk

• show running-config

Issue Type:’Switch Trunk Port Issues •Ensure trunks are configured correctly.

how to verify?

• show interfaces switchport

• show running-config interface

Issue Type: Switch Access Port Issues

how to verify?

• show ip interface brief

• show interfaces

Issue Type: Router Configuration Issues

how to verify?

inactive

When a VLAN is deleted, any ports assigned to that VLAN become _______

show interface interface-id switchport

Use the ________________ command to verify the VLAN membership of the port.

show interface trunk

Verify that the port connecting to the router is correctly configured as a trunk link using the _____________ command.

show ip interface brief

Verify the subinterface status using the ___________ command.