Chapter 4 Inter-VLAN Routing

What is legacy inter-vlan routing?

this is where a router has to have a physical interface link with a port associated with each VLAN

This quickly exhausts the physical interfaces on the router

This is not used in switched networks

What is Router-on-a-Stick Inter-VLAN Routing

This is a routing method that overcomes the limitation of inter-VLAN routing

This method only requires one physical Ethernet interface to route specific traffic between multiple VLANs

The router physical interface is configured with multiple subinterfaces to identify routable VLANs

What type of interface are a Cisco IOS router Ethernet Interfaces configured as in Router-on-a-Stick Inter-VLAN Routing? And what are the physical Ethernet interfaces connected to?

as 802.1Q trunk interfaces and connected to Layer 2 switch trunk ports

What are subinterfaces?

are software based virtual interfaces

True or False: Each subinterface in Router-on-a-Stick Inter-VLAN Routing is associated with multiple physical ethernet port links?

False, each subinterface is associated with a single physical Ethernet interface

Each subinterface is _____________ configured with an IP address and a VLAN assignment?

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

True or False: Subinterfaces are configured for different subnets that correspond to their VLAN assignment

True

What does Subinterfaces facilitate?

logical routing

Router-on-a-Stick Inter-VLAN Routing Process

1. When VLAN-tagged traffic enters the router interface, it is forwarded to what?

2. After a _________ decision is made based on the ___________ ____ __________ _________, the router determines the ________ __________ for the traffic.

3. If the exit interface is configured as an ___________ ____________, the data frames are _________ ________ with the new ___________, and sent back out the ________ _________.

1. forwarded to VLAN subinterface

2. After a routing decision is made based on the destination IP network address, the router determines the exit interface for the traffic.

3. If the exit interface is configured as an 802.Q subinterface, the data frames are VLAN-tagged with the new VLAN and sent back out the physical interface.

What is the number of VLANs supported by Router-on-a-Stick Inter-VLAN Routing?

50 VLANs

True or False Legacy Inter-VLAN Routing is not a legacy solution.

False, Legacy Inter-VLAN Routing is a legacy solution

Does Inter-VLAN Routing scale well?

NO - ports are exhausted very quickly on the router because each VLAN needs to have one assigned switch port connected to a router to serve as the default GW for that VLAN

What sized networks is Router-on-a-Stick acceptable for?

small to medium-sized networks

What sized networks are Layer 3 switch using switched virtual interfaces (SVIs) good for?

This is the most scalable VLAN routing option for medium to large organizations

What is Inter-VLAN Routing on a Layer 3 Switch

This is an inter-VLAN routing method that uses SVIs on a layer 3 switch to route packets to different VLANs

What is a SVI?

switched virtual interface

It performs the same functions for the VLAN as a router interface would

Provides layer 3 processing for packets that are sent to or from all switch ports associated with a VLAN

What are the advantages of Layer 3 switches for inter-VLAN routing?

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

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

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

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

5. They more commonly deployed in a campus LAN than routers

What is the only disadvantage of a layer 3 switch

they are much more expensive

True or False: You don't have to create a SVI for every routable VLAN?

False, A layer 3 SVI must be created for each of the routable VLANs.

Issue: Missing VLANs -- How would you fix this? -- How to verify this (what commands)?

-Create (or recreate) the VLAN if it does not exist

-Ensure host port is assigned to the correct VLAN

How to verify:

show vlan [brief]

show interfaces switchport

ping

Issue: Switch Trunk Port Issues -- How would you fix this? -- How to verify this (what commands)?

-Ensure trunks are configures correctly.

-Ensure port is a trunk port and enabled

How to verify:

show interfaces trunk

show running-config

Issue: Switch Access Port Issues -- How would you fix this? -- How to verify this (what commands)?

-Assign correct VLAN to access port.

-Ensure port is an access port and enabled.

-Host is incorrectly configured in the wrong subnet.

How to verify:

show interfaces switchport

show running-config interface

ipconfig

Issue: Router Configuration Issues -- How would you fix this? -- How to verify this (what commands)?

-Router subinterface IPv4 address is incorrectly configured.

-Router subinterface is assigned to the VLAN ID

How to verify:

show ip interface brief

show interfaces