Download The Internet and Its Uses

Implement InterVLAN Routing
LAN Switching and Wireless – Chapter 6
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Objectives

Explain to the satisfaction of a qualified instructor how
network traffic is routed between VLANs in a
converged network.

Configure inter-VLAN routing on a router to enable
communications between end-user devices on
separate VLANs

Troubleshoot common inter-VLAN connectivity issues.
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Introduction to VLAN Routing
 Traditionally, LAN routing has used routers with multiple physical
interfaces.
 Each interface needed to be connected to a separate network and
configured for a different subnet.
 In a traditional network that uses multiple VLANs to segment the network
traffic into logical broadcast domains
 Routing is performed by connecting different physical router interfaces to
different physical switch ports.
 Each switch interface would be assigned to a different static
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Conti…
 Routing options between VLANs
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Conti…
 1. PC1 on VLAN10 is communicating with PC3 on VLAN30 through router
R1.
 2. PC1 and PC3 are on different VLANs and have IP addresses on
different subnets.
 3. Router R1 has a separate interface configured for each of the VLANs.
 4. PC1 sends unicast traffic destined for PC3 to switch S2 on VLAN10,
where it is then forwarded out the trunk interface to switch S1.
 5. Switch S1 then forwards the unicast traffic to router R1 on interface
F0/0.
 6. The router routes the unicast traffic through to its interface F0/1, which
is connected to VLAN30.
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Conti…
 7. The router forwards the unicast traffic to switch S1 on VLAN 30.
 8. Switch S1 then forwards the unicast traffic to switch S2 through the
trunk link, after which switch S2 can then forward the unicast traffic to PC3
on VLAN30.
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Conti…
 Traditional inter-VLAN routing requires multiple physical interfaces on both
the router and the switch.
 However, not all inter-VLAN routing configurations require multiple
physical interfaces.
 Some router software permits configuring router interfaces as trunk links.
This opens up new possibilities for inter-VLAN routing.
 "Router-on-a-stick" is a type of router configuration in which a single
physical interface routes traffic between multiple VLANs on a network.
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Router-on-a-stick
 The router interface is configured to operate as a trunk link and is
connected to a switch port configured in trunk mode.
 The router performs the inter-VLAN routing by accepting VLAN tagged
traffic on the trunk interface coming from the adjacent switch and internally
routing between the VLANs using subinterfaces.
 The router then forwards the routed traffic-VLAN tagged for the destination
VLAN-out the same physical interface.
 Layer 3 Switches
 Some switches can perform Layer 3 functions, replacing the need for
dedicated routers to perform basic routing on a network.
 Multilayer switches are capable of performing inter-VLAN routing.
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Interfaces and Subinterfaces
 The routing process requires the source device to determine if the
destination device is local or remote to the local subnet.
 The source device accomplishes this by comparing the source and
destination addresses against the subnet mask.
 Once the destination address has been determined to be on a remote
network, the source device has to identify where it needs to forward the
packet to reach the destination device.
 The source device examines the local routing table to determine where it
needs to send the data.
 Typically, devices use their default gateway as the destination for all traffic
that needs to leave the local subnet.
 Note:Even though there are many steps in the process of inter-VLAN
routing when two devices on different VLANs communicate through a
router, the entire process happens in a fraction of a second.
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Advantages and Disadvantages of interfaces and
Subinterfaces
 Port Limits
 Performance
 Access Ports and Trunk Ports
 Cost
 Complexity
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Conti…
 Interface configuration
 R1# configure terminal
 R1(config)#interface fa0/0
 R1(config-if)#ipaddress 172.17.0.1 255.255.255.0
 R1(config-if)#no shutdown
 To verify
 R1#show ip route
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Conti…
 To overcome the hardware limitations of inter-VLAN routing based on
router physical interfaces, virtual subinterfaces and trunk links are used
 R1(config)#interface fa0/0.10
 R1(config-if)#encapsulation dot1q 10
 R1(config-if)#ip address 172.16.10.1 255.255.255.0
 R1(config-if)#interface fa0/0.30
 R1(config-if)#encapsulation dot1q 30
 R1(config)#interface fa0/0
 R1(config-if)#no shutdown
 To verify
 R1#show ip route
.
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Sub-interface configuration
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Configure Inter-VLAN Routing
 Switch configuration
 S1#configure terminal
 S1(config)#vlan 10
 S1(config-vlan)#vlan 30
 S1(config-vlan)#exit
 S1(config)#interface fa0/11
 S1(config-if)#switchport access vlan10
 S1(config-if)-iinterface fa0/4
 S1(config-if)#switchport access vlan 10
 S1(config)#interace fa0/6
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Conti…
 S1(config-if)#switcswitchport access vlan 30
 S1(config)#interface fa0/5
 S1(config-if)#switchport access vlan 30
 S1(config-if)#end
 Router Configuration
 R1# configure terminal
 R1(config)#interface fa0/0
 R1(config-if)#ipaddress 172.17.10.1 255.255.255.0
 R1(config-if)#no shutdown
 R1(config)#interface fa0/1
 R1(config-if)#ipaddress 172.17.30.1 255.255.255.0
 R1(config-if)#no shutdown
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Troubleshoot Common Inter-VLAN
Connectivity Issues
 Ensure that the switch port is on the correct VLAN
 Incase of router-on-a-stick ensure that the port mode is trunk
 show interface interface-id switchport and the show running-config
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Troubleshoot Common Inter-VLAN
Connectivity Issues
 Common IP Addressing Issues
 Ensure router’s interface IP to be from correct subnet/network
 Ensure PC’s IP to be from correct subnet/network
 Ensure correct subnet mask
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Summary
 Inter-VLAN routing is the process of routing information
between VLANs
 Inter-VLAN routing requires the use of a router or a
layer 3 switch
 Traditional inter-VLAN routing
Requires multiple router interfaces that are each connected to
separate VLANs
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Summary
 Router on a stick
this is an inter-VLAN routing topology that uses router sub
interfaces connected to a layer 2 switch.
Each Subinterface must be configured with:
An IP address
Associated VLAN number
 Configuration of inter VLAN routing
–Configure switch ports connected to router with correct VLAN
–Configure each router subinterface with the correct IP address
& VLAN ID
 Verify configuration on switch and router
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