Chapter 6
Inter-VLAN Routing
CCNA3-1
Chapter 6
Note for Instructors
• These presentations are the result of a collaboration among
the instructors at St. Clair College in Windsor, Ontario.
• Thanks must go out to Rick Graziani of Cabrillo College. His
material and additional information was used as a reference
in their creation.
• If anyone finds any errors or omissions, please let me know
at:
• tdame@stclaircollege.ca.
CCNA3-2
Chapter 6
Inter-VLAN Routing
Introducing Inter-VLAN Routing
CCNA3-3
Chapter 6
Introducing Inter-VLAN Routing
• What is Inter-VLAN Routing?
• Each VLAN is a unique broadcast domain.
• Computers on separate VLANs are, by default, not
able to communicate.
• Each VLAN is a unique IP subnetwork.
• To allow VLANs to communicate, we need a router to
communicate among separate broadcast domains and
unique IP subnetworks.
• Inter-VLAN routing, then, is a process of forwarding traffic
from one VLAN to another VLAN using a router.
CCNA3-4
Chapter 6
Introducing Inter-VLAN Routing
• Methods:
• Traditional Inter-VLAN Routing.
• Router-on-a-stick Inter-VLAN Routing.
• Switch Based Inter-VLAN Routing.
CCNA3-5
Chapter 6
Introducing Inter-VLAN Routing
• Traditional Inter-VLAN Routing:
• One router interface per VLAN.
Internally Routed to
the proper subnet.
VLAN
Tag
removed
Tagged
CCNA3-6
Chapter 6
Introducing Inter-VLAN Routing
• Router-on-a-stick Inter-VLAN Routing: Internally Routed to
• One router interface for all VLANs. the proper subnet.
VLAN
Tag
removed
Tagged
CCNA3-7
Chapter 6
Introducing Inter-VLAN Routing
• Layer 3 Switch Inter-VLAN Routing:
• Uses Switch Virtual Interfaces (SVI) to retag
the frame.
TagVLAN
removed
Tagged
(10)
CCNA3-8
Chapter 6
Interfaces and Subinterfaces
• Traditional Inter-VLAN Routing:
• Traditional routing requires routers to have multiple
physical interfaces to facilitate inter-VLAN routing.
• Each interface is also configured with an IP address for
the subnet associated with the particular VLAN that it is
connected to.
• In this configuration, network devices can use the router
as a gateway to access the devices connected to the
other VLANs.
CCNA3-9
Chapter 6
Interfaces and Subinterfaces
Router tags
Router
Traditional Inter-VLAN Routing the frame
Responds
for VLAN 30
Routing table:
And switches it
172.17.10.0 – F0/0
to Port F0/1.
172.17.30.0 – F0/1
Tagged
Tag
Removed
VLAN 10
CCNA3-10
Chapter 6
Interfaces and Subinterfaces
Traditional Inter-VLAN Routing
CCNA3-11
Chapter 6
Interfaces and Subinterfaces
• Traditional Inter-VLAN Routing:
• Traditional inter-VLAN
routing using physical
interfaces does have a
limitation.
• As the number of VLANs
increases on a network, the
physical approach of having one router interface per
VLAN quickly becomes hindered by the physical
hardware limitations of a router.
• Routers have a limited number of physical interfaces that
they can use to connect to different VLANs.
• It is very expensive to add an Ethernet Interface.
CCNA3-12
Chapter 6
Interfaces and Subinterfaces
• Router-on-a-stick Inter-VLAN Routing:
• Subinterfaces:
• Overcomes the hardware limitation of a router.
• Subinterfaces are software-based virtual interfaces
that are assigned to physical interfaces.
• Each subinterface is configured with its own IP
address, subnet mask, and unique VLAN assignment.
• Connected to a switch trunk link.
• Functionally the same as using the traditional routing
model.
CCNA3-13
Chapter 6
Interfaces and Subinterfaces
Router-on-a-stick Inter-VLAN Routing
Routing table:
172.17.10.0 – F0/0.10
172.17.30.0 – F0/0.30
Tagged
VLAN 30
Tagged
Tag
Tag
Removed
Removed
VLAN 30
10
CCNA3-14
Chapter 6
Interfaces and Subinterfaces
• Router-on-a-stick Inter-VLAN Routing:
• Configuring Subinterfaces:
• Similar to configuring physical interfaces.
• Create the subinterface.
• Assign it to a VLAN.
• Assign an IP Address.
• Enable the interface.
CCNA3-15
Chapter 6
Interfaces and Subinterfaces
• Router-on-a-stick Inter-VLAN Routing:
• Create the subinterface:
• The syntax for the subinterface is always the physical
interface, followed by a period and a subinterface
number.
• The subinterface number is configurable, but it is
typically associated to reflect the VLAN number.
R1(config)#interface [interface].nn
NOTE: The management VLAN must also be
configured if you wish to use it on multiple switches
that are not directly connected by trunk links.
CCNA3-16
Chapter 6
Interfaces and Subinterfaces
• Router-on-a-stick Inter-VLAN Routing:
• Assign it to a VLAN:
• Before assigning an IP Address, the interface must to
be configured to operate on a specific VLAN using the
proper encapsulation.
R1(config-subif)#encapsulation dot1q vlan-id
CCNA3-17
Chapter 6
Interfaces and Subinterfaces
• Router-on-a-stick Inter-VLAN Routing:
• Assign an IP Address:
• The IP Address assigned here will become the default
gateway for that VLAN.
R1(config-subif)#ip address [address] [mask]
CCNA3-18
Chapter 6
Interfaces and Subinterfaces
• Router-on-a-stick Inter-VLAN Routing:
• Enable the interface:
• Subinterfaces are not enabled individually.
• When the physical interface is enabled, all associated
subinterfaces are enabled.
R1(config-if)#no shutdown
CCNA3-19
Chapter 6
Interfaces and Subinterfaces
• Router-on-a-stick Inter-VLAN Routing:
• Configuring Subinterfaces:
VLAN 10
VLAN 30
Enable Interfaces
CCNA3-20
Chapter 6
Interfaces and Subinterfaces
• Router-on-a-stick Inter-VLAN Routing:
• Configuring Subinterfaces:
Planning!
CCNA3-21
Chapter 6
Interfaces and Subinterfaces
• Router Interface and Subinterface Comparison:
CCNA3-22
Chapter 6
Inter-VLAN Routing
Configuring Inter-VLAN Routing
(Putting It All Together)
CCNA3-23
Chapter 6
Configuring Inter-VLAN Routing
• Traditional Inter-VLAN Routing:
CCNA3-24
Chapter 6
Configuring Inter-VLAN Routing
• Traditional Inter-VLAN Routing:
CCNA3-25
Chapter 6
Configuring Inter-VLAN Routing
• Traditional Inter-VLAN Routing:
CCNA3-26
Chapter 6
Configuring Inter-VLAN Routing
• Router-on-a-stick Inter-VLAN Routing:
VLANs
Trunk in
Trunk
Native
VLAN
Interfaces
VLANs
CCNA3-27
Chapter 6
Configuring Inter-VLAN Routing
• Router-on-a-stick Inter-VLAN Routing:
VLAN 10
VLAN 30
Enable All
Subinterfaces
CCNA3-28
Chapter 6
Inter-VLAN Routing
Troubleshooting Inter-VLAN Routing
CCNA3-29
Chapter 6
Configuring Inter-VLAN Routing
VLAN 30 is working but VLAN 10
cannot
communicate with the
• Switch Configuration
Issues:
router or VLAN 30.
Interface F0/4 is still in
the default VLAN.
switchport access vlan 10
CCNA3-30
Chapter 6
Configuring Inter-VLAN Routing
Each of the configured
• Switch Configuration
Issues:
subinterfaces
is unable to
send or receive VLAN traffic.
Interface F0/5 is still in
the default VLAN.
switchport mode trunk
CCNA3-31
Chapter 6
Configuring Inter-VLAN Routing
PC1 cannot communicate with the
• Router Configuration
routerIssues:
interface and the router
cannot route to VLAN 30.
Switch port F0/4 is
for VLAN 10.
Switch port F0/9 is
Move the cable from F0/9 to F0/4.
assigned to the
default VLAN.
One of the most common
mistakes in Inter-VLAN routing.
CCNA3-32
Chapter 6
Configuring Inter-VLAN Routing
PC1 cannot communicate with the
routerIssues:
interface and the router
• Router Configuration
cannot route to VLAN 30.
CCNA3-33
Chapter 6
Configuring Inter-VLAN Routing
• IP Addressing Issues:
PC1 cannot communicate.
Incorrect IP address for
subnet 172.16.10.0/24.
Incorrect
Incorrect IP
subnet
address
mask
forfor
subnet
subnet172.16.10.0/24.
172.16.10.0/24.
CCNA3-34
Chapter 6