inter vl an routing
TRANSCRIPT
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Inter-VLAN routing
:44526754456830
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Topics
Routing network traffic between VLANs
Configuring a router for routing between
VLANs Troubleshoot inter-VLAN connectivity issues
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LAN Design
Basic Switch
Concepts
VLANs
VTP
STP
Inter-VLAN
routing
Wireless
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Inter VLAN routingSwitch keepsVLANs
separate.
Router can
route betweenVLANs
(subnets).
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Traditional inter-VLAN routing
The router has one physical port for each
VLAN.
Each port has an IP address on its ownVLAN.
Routing is the same as routing between any
subnets.
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Traditional inter-VLAN routing
PC1 has a
packet for
192.168.2.19
different
subnet
ARP request to
find MAC addressof default gateway
Send packet to
F0/0 of router
Router looks up
192.168.2.0 network
port F0/1
Router sends out
packet through F0/1 to
switchport F0/2
Switchport F0/2 is
on VLAN30 and
forwards to PC3.
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Traditional inter-VLAN routing
Trunks
between
switches.
No trunk to
router.
No tags on
frames to
router.
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Traditional Vs Router-on-stick (1)
Port Limits
Physical interfaces are configured to have oneinterface per VLAN on the network.
On networks with many VLANs, using a single router toperform inter-VLAN routing is not possible.
Instead, you could use multiple routers to perform inter-VLAN routing for all VLANs if avoiding the use ofsubinterfaces is a priority.
Subinterfaces allow a router to scale toaccommodate more VLANs than the physicalinterfaces permit..
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Traditional Vs Router-on-stick (2)
Performance
Because there is no contention for bandwidth on separate physical
interfaces, physical interfaces have better performance whencompared to using subinterfaces.
Traffic from each connected VLAN has access to the full bandwidthof the physical router interface connected to that VLAN for inter-VLAN routing.
When subinterfaces are used for inter-VLAN routing, the trafficbeing routed competes for bandwidth on the single physicalinterface.
On a busy network, this could cause a bottleneck forcommunication.
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Traditional Vs Router-on-stick (3)
Access Ports and Trunk Ports
Connecting physical interfaces for inter-VLAN
routing requires that the switch ports be configuredas access ports.
Subinterfaces require the switch port to be
configured as a trunk port so that it can accept
VLAN tagged traffic on the trunk link.
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Traditional Vs Router-on-stick (4)
Cost
Financially, it is more cost-effective to use subinterfacesoverseparate physical interfaces.
Routers that have many physical interfaces cost more thanrouters with a single interface.
Additionally, if you have a router with many physical interfaces,each interface is connected to a separate switch port, consumingextra switch ports on the network.
Switch ports are an expensive resource on high performanceswitches.
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Traditional Vs Router-on-stick (5)
Complexity
Using subinterfaces for inter-VLAN routing results in a less complexphysicalconfigurationthan using separate physical interfaces,
because there are fewer physical network cables interconnecting therouter to the switch.
On the other hand, using subinterfaces with a trunk port results in amore complex software configuration, which can be difficult totroubleshoot. If one VLAN is having trouble routing to other VLANs, you need to
check to see if the switch port is configured to be a trunk and verifythat the VLAN is not being filtered on any of the trunk links before itreaches the router interface.
You also need to check that the router subinterface is configured touse the correct VLAN ID and IP address for the subnet associatedwith that VLAN.
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Trunk to the router
You soon run out of router ports.
What about making a trunk link to the router?
A trunk link can be used with several VLANson the same physical port.
But each VLAN needs a different IP address.
So use subinterfaces, each with its own IPaddress.
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Router on a stick
R1 F0/0 has
subinterfaces,
one for each
VLAN.Each has its
own IP
address.
VLAN tags ontrunk.
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Subinterfaces
Subinterfaces take the interface name
followed by a dot and a number.
It is normal to use the VLAN number. If this
ties in with the IP address, even better.
E.g. interface f0/0.10
The subinterfaces each have an IP address.
The physical interface has no IP address
The physical interfaces needs no shutdown
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Configuring subinterfaces
R1(config)#interface f0/0.10
R1(config-subif)#encapsulation dot1q 10
R1(config-subif)#ip address 172.17.10.1255.255.255.0
(add any other subinterfaces)
R1(config-subif)#interface f0/0 R1(config-if)#no shutdown
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Subinterface considerations
Routers have a limited number of interfaces,
so subinterfaces help where there are many
VLANs.
Subinterfaces share the bandwidth on a
physical interface so can cause bottlenecks.
Cheaper to use subinterfaces.
Simpler physical layout but more complex
configuration with subinterfaces.
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Configuring Traditional Inter VLAN routing
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Configure router-on-a-stick inter VLAN routing
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Configure router-on-a-stick inter VLAN routing
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Configure router-on-a-stick inter VLAN routing
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Multilayer switch
A multilayer switch can
route between VLANs.
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Troubleshooting
Check physical connections
Check switchport VLAN assigment
Check trunking on switches Check IP addressing and subnetting scheme
in relation to VLANs
Check router subinterface configuration
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Troubleshooting inter VLAN
routing switch issues (1)
Incorrect VLAN
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Troubleshooting inter VLAN
routing switch issues (2)
Not configure as a trunk
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Troubleshooting inter VLAN
routing router issues
Incorrect VLAN on a stick
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Troubleshooting inter VLAN
routing IP addressing issues (1)
Incorrect IPAddressing
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Troubleshooting inter VLAN
routing IP addressing issues (2)
Incorrectsubnet mask
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The End