1. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE I Chapter 6 1 Implement Inter- VLAN Routing LAN Switching and Wireless – Chapter 6

2. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 2 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.

3. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 3 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

4. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 4 Conti…  Routing options between VLANs

5. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 5 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.

6. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 6 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.

7. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 7 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.

8. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 8 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.

9. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 9 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.

10. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 10 Advantages and Disadvantages of interfaces and Subinterfaces  Port Limits  Performance  Access Ports and Trunk Ports  Cost  Complexity

11. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 11 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

12. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 12 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.

13. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 13 Sub-interface configuration

14. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 14 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

15. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 15 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

16. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 16 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

17. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 17 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

18. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 18 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

19. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 19 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

20. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 20