chapter 6 lecture11 inter-vlan routing assistant professor pongpisit wuttidittachotti, ph.d. faculty...

Chapter 6

Lecture11

Inter-VLAN Routing

Assistant Professor Assistant Professor Pongpisit Wuttidittachotti, Ph.D.Pongpisit Wuttidittachotti, Ph.D.Faculty of Information TechnologyFaculty of Information TechnologyKing Mongkut's University of Technology North Bangkok (KMUTNB)King Mongkut's University of Technology North Bangkok (KMUTNB)

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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: – [email protected].

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Chapter 6

Inter-VLAN Routing

Introducing Inter-VLAN RoutingIntroducing Inter-VLAN Routing

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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.

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Chapter 6

Introducing Inter-VLAN Routing• Methods:

– Traditional Inter-VLAN Routing.– Router-on-a-stick Inter-VLAN Routing.– Switch Based Inter-VLAN Routing.

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Chapter 6

Introducing Inter-VLAN Routing• Traditional Inter-VLAN Routing:

– One router interface per VLAN.

VLAN VLAN TaggedTaggedVLAN VLAN

TaggedTagged

Internally Routed to Internally Routed to the proper subnet.the proper subnet.Internally Routed to Internally Routed to the proper subnet.the proper subnet.

TagTagremovedremoved


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Chapter 6

Introducing Inter-VLAN Routing• Router-on-a-stick Inter-VLAN Routing:

– One router interface for all VLANs.

VLAN VLAN TaggedTaggedVLAN VLAN

TaggedTagged

Internally Routed to Internally Routed to the proper subnet.the proper subnet.Internally Routed to Internally Routed to the proper subnet.the proper subnet.



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Chapter 6

Introducing Inter-VLAN Routing• Layer 3 Switch Inter-VLAN Routing:

– Uses Switch Virtual Interfaces (SVI) to retagthe frame.

VLAN VLAN TaggedTagged

(10)(10)

VLAN VLAN TaggedTagged

(10)(10)



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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.

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Chapter 6

Traditional Inter-VLAN RoutingTraditional Inter-VLAN RoutingTraditional Inter-VLAN RoutingTraditional Inter-VLAN Routing

Interfaces and Subinterfaces

TaggedTaggedVLAN 10VLAN 10TaggedTagged

VLAN 10VLAN 10TagTag

RemovedRemovedTagTag

RemovedRemoved

Router Router RespondsResponds

Router Router RespondsResponds

Routing table:Routing table:172.17.10.0 – F0/0172.17.10.0 – F0/0172.17.30.0 – F0/1172.17.30.0 – F0/1

Routing table:Routing table:172.17.10.0 – F0/0172.17.10.0 – F0/0172.17.30.0 – F0/1172.17.30.0 – F0/1

Router tagsRouter tagsthe framethe frame

for VLAN 30for VLAN 30And switches itAnd switches itto Port F0/1. to Port F0/1.

Router tagsRouter tagsthe framethe frame

for VLAN 30for VLAN 30And switches itAnd switches itto Port F0/1. to Port F0/1.

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Chapter 6

Interfaces and SubinterfacesTraditional Inter-VLAN RoutingTraditional Inter-VLAN RoutingTraditional Inter-VLAN RoutingTraditional Inter-VLAN Routing

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Chapter 6

Interfaces and Subinterfaces• Traditional Inter-VLAN Routing:

– Traditional inter-VLANrouting using physicalinterfaces does have alimitation.

– As the number of VLANsincreases on a network, thephysical 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. 1212

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.

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Chapter 6

Interfaces and SubinterfacesRouter-on-a-stick Inter-VLAN RoutingRouter-on-a-stick Inter-VLAN RoutingRouter-on-a-stick Inter-VLAN RoutingRouter-on-a-stick Inter-VLAN Routing




RemovedRemoved

Routing table:Routing table:172.17.10.0 – F0/0.10172.17.10.0 – F0/0.10172.17.30.0 – F0/0.30172.17.30.0 – F0/0.30

Routing table:Routing table:172.17.10.0 – F0/0.10172.17.10.0 – F0/0.10172.17.30.0 – F0/0.30172.17.30.0 – F0/0.30


VLAN 30VLAN 30

TagTagRemovedRemoved

TagTagRemovedRemovedTaggedTagged

VLAN 30VLAN 30TaggedTagged



RemovedRemoved

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Chapter 6


– Configuring Subinterfaces:• Similar to configuring physical interfaces.

– Create the subinterface.– Assign it to a VLAN.– Assign an IP Address.– Enable the interface.

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Chapter 6


– 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.

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Chapter 6


– 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

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Chapter 6


– Assign an IP Address:• The IP Address assigned here will become the default

gateway for that VLAN.

R1(config-subif)#ip address [address] [mask]

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Chapter 6


– Enable the interface:• Subinterfaces are not enabled individually.• When the physical interface is enabled, all associated

subinterfaces are enabled.

R1(config-if)#no shutdown

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Chapter 6


– Configuring Subinterfaces:

VLAN 10VLAN 10VLAN 10VLAN 10VLAN 10VLAN 10VLAN 10VLAN 10

VLAN 30VLAN 30VLAN 30VLAN 30



Enable InterfacesEnable InterfacesEnable InterfacesEnable Interfaces

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Chapter 6


– Configuring Subinterfaces:

Planning!Planning!Planning!Planning!

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Chapter 6

Interfaces and Subinterfaces• Router Interface and Subinterface Comparison:

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Chapter 6

Inter-VLAN Routing

Configuring Inter-VLAN RoutingConfiguring Inter-VLAN Routing(Putting It All Together)(Putting It All Together)

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Chapter 6

Configuring Inter-VLAN Routing• Traditional Inter-VLAN Routing:

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Chapter 6

Configuring Inter-VLAN Routing

• Traditional Inter-VLAN Routing:

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Chapter 6


• Traditional Inter-VLAN Routing:

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Chapter 6


• Router-on-a-stick Inter-VLAN Routing:VLANsVLANsVLANsVLANs

TrunkTrunkTrunkTrunk

InterfacesInterfacesInterfacesInterfaces

VLANsVLANsVLANsVLANs

Trunk in Native Trunk in Native VLANVLAN

Trunk in Native Trunk in Native VLANVLAN

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Chapter 6

Configuring Inter-VLAN Routing• Router-on-a-stick Inter-VLAN Routing:



Enable All Enable All SubinterfacesSubinterfaces

Enable All Enable All SubinterfacesSubinterfaces

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Chapter 6

Inter-VLAN RoutingTroubleshooting Inter-VLAN RoutingTroubleshooting Inter-VLAN Routing

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Chapter 6

Configuring Inter-VLAN Routing• Switch Configuration Issues:

VLAN 30 is working but VLAN 10 VLAN 30 is working but VLAN 10 cannot communicate with the router cannot communicate with the router

or VLAN 30.or VLAN 30.

VLAN 30 is working but VLAN 10 VLAN 30 is working but VLAN 10 cannot communicate with the router cannot communicate with the router

or VLAN 30.or VLAN 30.

Interface F0/4 is still in Interface F0/4 is still in the default VLAN.the default VLAN.

Interface F0/4 is still in Interface F0/4 is still in the default VLAN.the default VLAN.

switchport access vlan 10switchport access vlan 10switchport access vlan 10switchport access vlan 10

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Chapter 6


• Switch Configuration Issues:

Each of the configured Each of the configured subinterfaces is unable to subinterfaces is unable to

send or receive VLAN traffic.send or receive VLAN traffic.

Each of the configured Each of the configured subinterfaces is unable to subinterfaces is unable to

send or receive VLAN traffic.send or receive VLAN traffic.

Interface F0/4 is still in the Interface F0/4 is still in the default VLAN.default VLAN.

Interface F0/4 is still in the Interface F0/4 is still in the default VLAN.default VLAN.

switchport mode trunkswitchport mode trunkswitchport mode trunkswitchport mode trunk

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F0/4F0/4

Chapter 6


• Router Configuration Issues:PC1 cannot communicate with the PC1 cannot communicate with the

router interface and the router router interface and the router cannot route to VLAN 30.cannot route to VLAN 30.

PC1 cannot communicate with the PC1 cannot communicate with the router interface and the router router interface and the router

cannot route to VLAN 30.cannot route to VLAN 30.

Switch port F0/4 is Switch port F0/4 is for VLAN 10.for VLAN 10.

Switch port F0/4 is Switch port F0/4 is for VLAN 10.for VLAN 10.

Move the cable from F0/9 to F0/4.Move the cable from F0/9 to F0/4.Move the cable from F0/9 to F0/4.Move the cable from F0/9 to F0/4.

One of the most common mistakes One of the most common mistakes in Inter-VLAN routing.in Inter-VLAN routing.

One of the most common mistakes One of the most common mistakes in Inter-VLAN routing.in Inter-VLAN routing.

Move the cable from F0/9 to F0/4.Move the cable from F0/9 to F0/4.Move the cable from F0/9 to F0/4.Move the cable from F0/9 to F0/4.

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Chapter 6


• Router Configuration Issues: PC1 cannot communicate with PC1 cannot communicate with the router interface and the router the router interface and the router


PC1 cannot communicate with PC1 cannot communicate with the router interface and the router the router interface and the router


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Chapter 6

Configuring Inter-VLAN Routing• IP Addressing Issues:

Incorrect IP address for Incorrect IP address for subnet 172.16.10.0/24.subnet 172.16.10.0/24.Incorrect IP address for Incorrect IP address for subnet 172.16.10.0/24.subnet 172.16.10.0/24.

Incorrect IP address for Incorrect IP address for subnet 172.16.10.0/24.subnet 172.16.10.0/24.Incorrect IP address for Incorrect IP address for subnet 172.16.10.0/24.subnet 172.16.10.0/24.Incorrect subnet mask for Incorrect subnet mask for subnet 172.16.10.0/24.subnet 172.16.10.0/24.

Incorrect subnet mask for Incorrect subnet mask for subnet 172.16.10.0/24.subnet 172.16.10.0/24.

PC1 cannot communicate.PC1 cannot communicate.PC1 cannot communicate.PC1 cannot communicate.

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chapter 6 lecture11 inter-vlan routing assistant professor pongpisit wuttidittachotti, ph.d. faculty...

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