Exploration 3-chapter 6

Router-base Inter- VLAN routing is a process for forwarding network traffic from one VLAN to other VLAN using a router.
“Router-on-a-stick” is a type of router configuration in which a single physical interface routes traffic between multiple VLANs on a network.
Subinterfaces are multiple virtual interfaces, associated with one physical interface. Unlike a typical physical interface, subinterfaces are not enabled with the no shutdown command at the subinterface configuration mode level of the Cisco IOS software.
when the physical interface is enabled with the no shutdown command, all the configured subinterfaces are enabled. Likewise, if the physical interface is disabled, all subinterfaces are disabled.
physical interfaces and subinterfaces
Port Limits
Physical interfaces are configured to have one interface per VLAN on the network. On networks with many VLANs, using a single router to perform inter-VLAN routing is not possible.
Subinterfaces allow a router to scale to accommodate more VLANs than the physical interfaces permit.
Performance
Because there is no contention for bandwidth on separate physical interfaces, physical interfaces have better performance when compared to using subinterfaces. Traffic from each connected VLAN has access to the full bandwidth of the physical router interface connected to that VLAN for inter-VLAN routing.
When subinterfaces are used for inter-VLAN routing, the traffic being routed competes for bandwidth on the single physical interface. On a busy network, this could cause a bottleneck for communication.
Access Ports and Trunk Ports
Connecting physical interfaces for inter-VLAN routing requires that the switch ports be configured as 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.
Using subinterfaces, many VLANs can be routed over a single trunk link rather than a single physical interface for each VLAN.
Cost
it is more cost-effective to use subinterfaces over separate physical interfaces. Routers that have many physical interfaces cost more than routers with a single interface.
Complexity
Using subinterfaces for inter-VLAN routing results in a less complex physical configuration than using separate physical interfaces, because there are fewer physical network cables interconnecting the router to the switch.
The Ping Test
The ping command sends an ICMP echo request to the destination address. When a host receives an ICMP echo request, it responds with an ICMP echo reply to confirm that it received the ICMP echo request. The ping command calculates the elapsed time using the difference between the time the ping was sent and the time the echo reply was received.
PC>ping 172.17.30.23
The Tracert Test
Tracert is a useful utility for confirming the routed path taken between two devices. On UNIX systems, the utility is specified by traceroute. Tracert also uses ICMP to determine the path taken, but it uses ICMP echo requests with specific time-to-live values defined on the frame.
PC>tracert 172.17.30.23
the show running-config and the show interface interface-id switchport commands are useful for identifying VLAN assignment and port configuration issues.
• Inter-VLAN routing is accomplished using a dedicated router or a multilayer switch. Inter-VLAN routing facilitates communication between devices isolated by VLAN boundaries.
• Traditional inter-VLAN routing requires that a router be configured with multiple physical interfaces, each connected physically to separate VLANs on a switch.
• The router-on-a-stick model provides similar functionality to the traditional inter-VLAN routing at reduced cost but provides lower performance on busy networks.
• Traditional inter-VLAN routing uses the physical interfaces of the router, while router-on-a-stick inter-VLAN routing uses logical subinterfaces of the physical interface.
• Configure switch ports connected to the router for the appropriate VLANs. Configure each router interface with the subnet associated with each VLAN.
• Configure each subinterface on a router-on-a-stick with a unique VLAN ID and corresponding IP address to match the subnet associated with the VLAN.
• To reduce the risk of switch, router, or IP address configuration problems, verify the configuration of each device.

Advertisement