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CCNA 200-120 Training2.7 Configure and verify trunking on Cisco switches

Jose Luis Flores / Amel Walkinshaw

Aug, 2015

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2.0 LAN Switching Technologies

2.7 Configure and verify trunking on Cisco switches

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2.7 Configure and verify trunking on Cisco switches

Trunking interacts with other features in these ways:• A trunk port cannot be a secure port•A trunk port cannot be a tunnel port •Trunk ports can be grouped into EtherChannel port groups, but all trunks in the group must have the same configuration. When a group is first created, all ports follow the parameters set for the first port to be added to the group. If you change the configuration of one of these parameters, the switch module propagates the setting that you entered to all ports in the group: – allowed-VLAN list– STP port priority for each VLAN– STP Port Fast setting

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2.7 Configure and verify trunking on Cisco switches

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2.7 Configure and verify trunking on Cisco switches

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2.7 Configure and verify trunking on Cisco switches

Switch(config)# interface fastethernet0/1 Switch(config-if)# switchport trunk allowed vlan remove 2Switch(config-if)# end

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2.7 Configure and verify trunking on Cisco switches

Configuring the Native VLAN for Untagged Traffic

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2.7 Configure and verify trunking on Cisco switches

Configuring Trunk Ports for Load Sharing

Load sharing divides the bandwidth supplied by parallel trunks that connect switches. To avoid loops, STP normally blocks all but one parallel link between switches. Using load sharing, you divide the traffic between the links according to the VLAN to which the traffic belongs. You configure load sharing on trunk ports that have STP enabled by using STP port priorities or STP path costs. For load sharing using STP port priorities, both load-sharing links must be connected to the same switch module. For load sharing using STP path costs, each load-sharing link can be connected to the same switch module or to two different switch modules.

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2.7 Configure and verify trunking on Cisco switches

Load Sharing Using STP Port PrioritiesWhen two ports on the same switch module form a loop, the switch module uses the STP port priority to decide which port is enabled and which port is in a blocking state. You can set the priorities on a parallel STP trunk port so that the port carries all the traffic for a given VLAN. The trunk port with the higher priority (lower values) for a VLAN is forwarding traffic for that VLAN. The trunk port with the lower priority (higher values) for the same VLAN remains in a blocking state for that VLAN. One trunk port sends or receives all traffic for the VLAN.Figure 11-3 shows two trunks connecting supported switches. In this example, the switches are configured as follows:•VLANs 8 through 10 are assigned a port priority of 16 on Trunk 1•VLANs 3 through 6 retain the default port priority of 128 on Trunk 1•VLANs 3 through 6 are assigned a port priority of 16 on Trunk 2•VLANs 8 through 10 retain the default port priority of 128 on Trunk 2In this way, Trunk 1 carries traffic for VLANs 8 through 10, and Trunk 2 carries traffic for VLANs 3 through 6. If the active trunk fails, the trunk with the lower priority takes over and carries the traffic for all of the VLANs. No duplication of traffic occurs over any trunk port.

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2.7 Configure and verify trunking on Cisco switches

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2.7 Configure and verify trunking on Cisco switches

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2.7 Configure and verify trunking on Cisco switches

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2.7 Configure and verify trunking on Cisco switches

Which are valid modes for a switch port used as a VLAN trunk? (Choose three. )A. transparentB. autoC. onD. desirableE. blockingF. forwarding

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2.7 Configure and verify trunking on Cisco switches

Which three of these statements regarding 802. 1Q trunking are correct? (Choose three. )A. 802. 1Q native VLAN frames are untagged by default.B. 802. 1Q trunking ports can also be secure ports.C. 802. 1Q trunks can use 10 Mb/s Ethernet interfaces.D. 802. 1Q trunks require full-duplex, point-to-point connectivity.E. 802. 1Q trunks should have native VLANs that are the same at both ends.

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2.7 Configure and verify trunking on Cisco switches

Explanation:

By default, 802. 1Q trunk defined Native VLAN in order to forward unmarked frame. Switches can forward Layer 2 frame from Native VLAN on unmarked trunks port. Receiver switches will transmit all unmarked packets to Native VLAN. Native VLAN is the default VLAN configuration of port. Note for the 802. 1Q trunk ports between two devices, the same Native VLAN configuration is required on both sides of the link. If the Native VLAN in 802. 1Q trunk ports on same trunk link is properly configured, it could lead to layer 2 loops. The 802. 1Q trunk link transmits VLAN information through Ethernet.

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2.7 Configure and verify trunking on Cisco switches

What are three advantages of VLANs? (Choose three. )A. VLANs establish broadcast domains in switched networks.B. VLANs utilize packet filtering to enhance network security.C. VLANs provide a method of conserving IP addresses in large networks.D. VLANs provide a low-latency internetworking alternative to routed networks.E. VLANs allow access to network services based on department, not physical location.F. VLANs can greatly simplify adding, moving, or changing hosts on the network.

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Explanation:VLAN technology is often used in practice, because it can better control layer2 broadcast to improve network security. This makes network more flexible and scalable. Packet filtering is a function of firewall instead of VLAN.

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2.7 Configure and verify trunking on Cisco switches

Cisco Catalyst switches CAT1 and CAT2 have a connection between them using ports FA0/13. An 802. 1Q trunk is configured between the two switches. On CAT1, VLAN 10 is chosen as native, but on CAT2 the native VLAN is not specified.What will happen in this scenario?A. 802. 1Q giants frames could saturate the link.B. VLAN 10 on CAT1 and VLAN 1 on CAT2 will send untagged frames.C. A native VLAN mismatch error message will appear.D. VLAN 10 on CAT1 and VLAN 1 on CAT2 will send tagged frames.

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2.7 Configure and verify trunking on Cisco switches

Explanation:A “native VLAN mismatch” error will appear by CDP if there is a native VLAN mismatch on an 802. 1Q link.“VLAN mismatch” can cause traffic from one vlan to leak into another vlan.

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A technician is troubleshooting host connectivity issues on the switches. The hosts in VLANs 10 and 15 on Sw11 are unable to communicate with hosts in the same VLANs on Sw12. Hosts in the Admin VLAN are able to communicate. The port-to-VLAN assignments are identical on the two switches.What could be the problem?A. The Fa0/1 port is not operational on one of the switches.B. The link connecting the switches has not been configured as a trunk.C. At least one port needs to be configured in VLAN 1 for VLANs 10 and 15 to be able to communicate.D. Port FastEthernet 0/1 needs to be configured as an access link on both switches.E. A router is required for hosts on SW11 in VLANs 10 and 15 to communicate with hosts in the same VLAN on Sw12.

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2.7 Configure and verify trunking on Cisco switches

Explanation:In order for hosts in the same VLAN to communicate with each other over multiple switches, those switches need to be configured as trunks on their connected interfaces so that they can pass traffic from multiple VLANs.

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On a corporate network, hosts on the same VLAN can communicate with each other, but they are unable to communicate with hosts on different VLANs.What is needed to allow communication between the VLANs?A. a router with subinterfaces configured on the physical interface that is connected to the switchB. a router with an IP address on the physical interface connected to the switchC. a switch with an access link that is configured between the switchesD. a switch with a trunk link that is configured between the switches

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Bibliography

• http://www.ciscopress.com/articles/article.asp?p=102157&seqNum=6• http://www.cisco.com/c/en/us/td/docs/routers/connectedgrid/switch_module_swcg/cgr-esm-configuration/config_vlans.html

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Q&A