CCNA 2 v6 RSE Chapter 6 Exam Online

Security, cost reduction, and improved IT staff efficiency are all benefits of using VLANs, along with higher performance, broadcast storm mitigation, and simpler project and application management. End users are not usually aware of VLANs, and VLANs do require configuration. Because VLANs are assigned to access ports, they do not reduce the number of trunk links.

A native VLAN is the VLAN that does not receive a VLAN tag in the IEEE 802.1Q frame header. Cisco best practices recommend the use of an unused VLAN (not a data VLAN, the default VLAN of VLAN 1, or the management VLAN) as the native VLAN whenever possible.

VLAN trunk links are used to allow all VLAN traffic to propagate between devices such as the link between a switch and a server that has an 802.1Q-capable NIC. Switches can also utilize trunk links to routers, servers, and to other switches.

A native VLAN is used to forward untagged frames that are received on a Cisco switch 802.1Q trunk port. Untagged frames that are received on a trunk port are not forwarded to any other VLAN except the native VLAN.

When the no switchport access vlan command is entered, the port is returned to the default VLAN 1. The port will remain active as a member of VLAN 1, and VLAN 30 will still be intact, even if no other ports are associated with it.

The command no vlan vlan-id is used to remove a particular VLAN from a switch. The delete vlan.dat and delete flash:vlan.dat commands will remove all VLANs after reloading the switch.

If the VLAN that is associated with a port is deleted, the port becomes inactive and cannot communicate with the network any more. To verify that a port is in an inactive state, use the show interfaces switchport command.

Extended range VLANs are stored in the running-configuration file by default and must be saved after being configured. Extended VLANs use the VLAN IDs from 1006 to 4094. ​

The switchport trunk allowed vlan 30 command allows traffic that is tagged with VLAN 30 across the trunk port. Any VLAN that is not specified in this command will not be allowed on this trunk port.

Because PC-A and PC-B are connected to different switches, traffic between them must flow over the trunk link. Trunks can be configured so that they only allow traffic for particular VLANs to cross the link. In this scenario, VLAN 60, the VLAN that is associated with PC-A and PC-B, has not been allowed across the link, as shown by the output of show interfaces trunk.

When configuring 802.1Q trunk links, the native VLAN must match on both sides of the link, or else CDP error messages will be generated, and traffic that is coming from or going to the native VLAN will not be handled correctly.

Multiple VLANs are supported with legacy inter-VLAN routing, but each VLAN requires its own Ethernet router link. Ethernet ports are limited on a router. That is why the router-on-a-stick model evolved. The user VLAN should never be the same number as the management VLAN and using a Layer 3 switch as a router is a modern technique, not a legacy one.

Router-on-a-stick inter-VLAN routing does not scale beyond 50 VLANs. The router can receive VLAN-tagged packets and send VLAN-tagged packets to a destination. Router-on-a-stick inter-VLAN routing can utilize a single router interface as a trunk link to receive and forward VLAN traffic and does not require multiple interfaces.

The IP address 192.168.1.85 belongs to network 192.168.1.64/27. The valid host addresses in this network include 192.168.1.65 to 192.168.1.94. The IP address configured for the subinterface of Fa0/1.2 is in the same network, which serves as the default gateway for the VLAN 2.

The router is used to route between the two VLANs, thus switch port G0/1 needs to be configured in trunk mode.

With legacy inter-VLAN routing, different physical router interfaces are connected to different physical switch ports. The switch ports that connect to the router are in access mode, each belonging to a different VLAN. Switches can have ports that are assigned to different VLANs, but communication between VLANs requires routing function from the router.

Based on the IP addresses and masks given, the PC, printer, IP phone, and switch management VLAN are all on different VLANs. This situation will require four subinterfaces on the router.

The IP address and the encapsulation type should be assigned to each router subinterface in a router-on-a-stick inter-VLAN topology.

With router-on-a-stick, inter-VLAN routing is performed by a router with a single router interface that is connected to a switch port configured with trunk mode. Multiple subinterfaces, each configured for a VLAN, can be configured under the single physical router interface. Switches can have ports that are assigned to different VLANs, but communication between those VLANs requires routing function from the router. A multilayer switch is not used in a router-on-a-stick approach to inter-VLAN routing.

To add an IP phone, the following commands should be added to the switch port:
SW3(config-vlan)# vlan 150
SW3(config-vlan)# name voice
SW3(config-vlan)# int fa0/20
SW3(config-if)# switchport mode access
SW3(config-if)# mls qos trust cos
SW3(config-if)# switchport access vlan 150

The show vlan brief command will provide information displaying the VLAN assignment and membership for all switch ports on a switch.

he subinterface GigabitEthernet 0/0.30 has an IP address that does not correspond to the VLAN addressing scheme. The physical interface GigabitEthernet 0/0 does not need an IP address for the subinterfaces to function. Subinterfaces do not require the no shutdown command.

The IEEE 802.1Q standard header includes a 4-byte VLAN tag:
Type – A 2-byte value called the tag protocol ID (TPID) value.
User priority – A 3-bit value that supports level or service implementation.
Canonical Format Identifier (CFI) – A 1-bit identifier that enables Token Ring frames to be carried across Ethernet links.
VLAN ID (VID) – A 12-bit VLAN identification number that supports up to 4096 VLAN IDs.

Only hosts in the same VLAN as PC-C (VLAN 20) will receive the broadcast. The trunk links will carry the broadcast to ALS2 where it will be send to PC-D and PC-E, which are also in VLAN 20. PC-A, PC-B, and PC-F are not in the same VLAN as PC-C. This information can be verified by issuing the show vlan and show interfaces trunk commands.