CCNA v5.0 modul 2 Chapter: 5 - Inter-VLAN Routing

1. Inter-VLAN Routing

1.1 Whats is Inter-VLAN Routing?

Process of forwarding network traffic from one VLAN to another VLAN using routing is known as inter-VLAN routing. L3 operation that can to done in tree way form.

1.2 Inter-Vlan routing Type:

·      Legacy:  A router with many interfaces each interface own a VLAN ID and the router takes the task to forwarding frame to VLAN ID destination.

·      Router-on-stick: Switch connected to a router with only one interface configured as trunk. The router performs inter-VLAN routing by accepting VLAN-tagged traffic. The internal routing is accomplished using subinterfaces. (Software-based virtual interfaces).

·      Multilayer-switch: Multilayer switches can perform Layer 2 and Layer 3 functions, replacing the need for dedicated routers. Multilayer switches support dynamic routing and inter-VLAN routing.

2. Configure Legacy Inter-VLAN Routing

2.1 switch configuration

Each of its physical interfaces connected:

-       Unique VLAN

-       And IP address for the subnet associated with the particular VLAN to which it is connected.

Devices use the interface IP as a gateway to access the devices connected to the other VLANs.

The routing process requires the source device to determine if the destination device is local or remote to the local subnet.  Done by comparing the source and destination IP addresses against the subnet.

S1(config)#vlan 10 S1(config-vlan)#vlan 30 S1(config-vlan)#interface f0/11 S1(config-if)#switchport access vlan 10 S1(config-if)#interface f0/4 S1(config-if)#switchport access vlan 10 S1(config-if)#interface f0/6 S1(config-if)#switchport access vlan 30 S1(config-if)#interface f0/5 S1(config-if)#switchport access vlan 30 S1(config-if)#end

2.2 router configuration

The process is repeated for all router interfaces. Each router interface must be assigned to a unique subnet for routing to occur.  After the IP addresses are assigned to the physical interfaces and the interfaces are enabled, the router is capable of performing inter-VLAN Routing table using the show ip route.

R1(config)#interface g0/0 R1(config-if)#ip address 172.17.10.1 255.255.255.0 R1(config-if)#no shutdown R1(config)#interface g0/1 R1(config)#ip address 172.17.30.1 255.255.255.0 R1(config)#no shutdown R1(config)#end

3. Configure Router-on-a-Stick Inter-VLAN Routing

3.1 Switch configuration

This technique is termed router-on-a-stick and uses virtual subinterfaces on the router to overcome the hardware limitations based on physical router interfaces.

Each subinterface is configured independently with its own IP address and subnet mask.

The physical interface of the router must be connected to a trunk link on the adjacent switch

S1(config)#vlan 10 S1(config-vlan)#vlan 30 S1(config-vlan)#interface f0/5 S1(config-if)#switchport mode trunk S1(config-if)#end Note: The router does not support the Dynamic Trunking Protocol (DTP), which is used by switches, so the following commands cannot be used: S1(config-if)#switchport mode dynamic auto S1(config-if)#switchport mode dynamic desirable.

3.2 Configure Router-on-a-Stick: Router Subinterface Configuration

Individual subinterfaces can be administratively shut down with the shutdown command. By default, Cisco routers are configured to route traffic between local subinterfaces. R1# show vlans Verify: Ping: End to end device ICMP pakets Traceroute: Hops information path+ICMP

R1(config)#interface g0/0.10 R1(config-subif)#encapsulation dot1q 10 R1(config-subif)#ip address 172.17.10.1 255.255.255.0 R1(config-subif)#interface g0/0.30 R1(config-subif)#encapsulation dot1q 30 R1(config-subif)#ip address 172.17.30.1 255.255.255.0 R1(config)#interface g0/0 R1(config-if)#no shutdown

4. Troubleshoot Inter-VLAN Routing

4.1 Switch Port Issues

- Legacy: verify the correct VLAN on all interfaces

- Router-on-a-Stick: Verify connection between switch and router is correctly set on mode trunk.

  Verify the entire path correctly setup VLAN to reach the router final destination.

4.2 Verify Switch Configurations

S1#show interfaces interface-id switchport

S1#show running-config

Verify :

-Administrative mode:

-Access mode vlan:

4.3 Interface Issues

Verify: Physical router interface is not in wrong switch port.

4.4 Verify Router Configurations

With router-on-a-stick configurations, a common problem is assigning the wrong VLAN ID to the subinterface. Using the show interfaces and the show running-config commands can be useful in troubleshooting this type of issue, as shown in the figure.

Verify correct setup: encapsulation dot1q (correct vlan). Shows up with show interfaces and show run

4.5 IP Addressing Issues - IP Address and Subnet Mask

Each interface, or subinterface, must be assigned an IP address corresponding to the subnet to which it is connected.

R1# show ip interface

5. Layer 3 switching

5.1 Introduction to Layer 3 Switching

Layer 3 switches usually have packet-switching throughputs in the millions of packets per second (pps), whereas traditional routers provide packet switching in the range of 100,000 pps to more than 1 million pps.

All Catalyst multilayer switches support the following types of Layer 3 interfaces:

-       Routed port: Layer 3 port

-       Switch Virtual Interface (SVI): A virtual VLAN interface for inter-VLAN routing

High-performance switches (Layer 3 + Cisco Express Forwarding):

- Catalyst 6500

- Catalyst 4500

Catalyst 2960 : IOS < 12.2(55) support Static routing.

All members of the Catalyst 3560 and 4500 families of switches use Layer 2 interfaces by default.

Members of the Catalyst 6500 family of switches running Cisco IOS use Layer 3 interfaces by default

5.2 Inter-VLAN Routing with Switch Virtual Interfaces

In the early days speed of switchs prompted designer to extend layer 2 to access, distribution and core layer. This topology created loop issues. To solve these issues, spanning-tree technologies were used to prevent loops while still enabling flexibility and redundancy in inter-switch connections. Today, routing can be performed at hardware speed. One consequence of this evolution is that routing can be transferred to the core and the distribution layers without impacting network performance. Users on VLAN and on different subnets are routed with distribution switches as Layer 3 gateways. Every VLAN have this own IP address.
	By default, an SVI is created for the default VLAN (VLAN 1) to permit remote switch administration

Whenever the SVI is created, ensure that particular VLAN is present in the VLAN database

Reasons to configure SVI: 

·      To provide a gateway for a VLAN so that traffic can be routed into or out of that VLAN

·      To provide Layer 3 IP connectivity to the switch

·      To support routing protocol and bridging configurations

Advantages of SVIs (the only disadvantage is that multilayer switches are more expensive): 

·      It is much faster than router-on-a-stick, because everything is hardware switched and routed.

·      No need for external links from the switch to the router for routing.

·      Not limited to one link. Layer 2 EtherChannels can be used between the switches to get more bandwidth.

·      Latency is much lower, because it does not need to leave the switch.

5.3 Inter-VLAN Routing with Routed Ports

Routed Ports and Access Ports on a Switch

Routed is a physical port that acts like an interface in router. Routed port is not associated with a particular VLAN Layer 2 functionality has been removed (STP) Routed ports on a Cisco IOS switch do not support subinterfaces. Routed ports are used for point-to-point links. configure routed ports: S1(config-if)#no switchport

Following are some of the advantages of routed ports:  A multilayer switch can have both SVI and routed ports in a single switch. Multilayer switches forward either Layer 2 or Layer 3 traffic in hardware, helping to perform routing faster.

Note: Routed ports are not supported on Catalyst 2960 Series switches.

A Catalyst 2960 switch can function as a Layer 3 device and route between VLANs and a limited number of static routes.

The Cisco Switch Database Manager (SDM) provides multiple templates for the 2960 switch. The templates can be enabled to support specific roles depending on how the switch is used in the network. For example, the sdm lanbase-routing template can be enabled to allow the switch to route between VLANs and to support static routing.

show sdm prefer

The SDM template can be changed in global configuration mode with the sdm prefer command.

Enabling routing IPv4 routing functionality on a 2960

S1(config)#interface f0/6 S1(config-if)#switchport access vlan 2 S1(config-if)#interface vlan 1 S1(config-if)#ip address 192.168.1.1 255.255.255.0 S1(config-if)#interface vlan 2 S1(config-if)#ip address 192.168.2.1 255.255.255.0 S1(config-if)#no shutdown IPv4:S1(config)#ip routing IPv6:S1(config)# ipv6 unicast-routing Verify: Show ip route