Term
| What are 2 methods that Cisco Catalyst switches use to mark frames with a respective VLAN for transmission across a trunk interface? |
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Definition
| Cisco's propreitary protocal, ISL, and IEEE 802.1Q |
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Term
| Of the 2 trunking protocols used by Catalyst switches, which is considered an encapsulation method for trunking? Which is considered a tagging method? |
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Definition
| ISL is considered an encapsulation method for trunking, whereas 802.1Q trunking uses a tagging method. |
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Term
| Which trunking protocol must calculate a new FCS for each frame sent and why? |
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Definition
| The 802.1Q trunking protocol frames place an additional 4-byte tag into the original packet, so a Catalyst switch must calculate a new FCS |
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Term
| Of the 2 different trunking protocols, which is Cisco propreitary and which is an industary-standard? |
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Definition
| Inter-Switch Link (ISL) is Cisco propiertary, and IEEE 802.1Q is an industry-standard. |
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Term
| What is the header size of a ISL frame? |
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Definition
| The header encapsulation is 26 bytes, plus an additional 4 bytes for the new CRC |
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Term
| Explain why ISL frames contain 2 FCS fields? |
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Definition
| The original transmitting device generates one FCS field, and the ISL trunk port generates the other FCS field. ISL encapsulates the frame without modifying its contents. |
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Term
| What are some architectural advantages of 802.1Q over ISL? |
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Definition
- 802.1Q has a smaller frame overhead then ISL, 4 bytes versus 30 bytes. - 802.1Q is a widely support industry-standard protocol - 802.1Q has the support for 802.1p fields for QoS |
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Term
| Which trunking protocol modifies the original frame, which results in having to recalculate the CRC value for the entire frame? |
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Definition
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Term
| What happens is a non-802.1Q-enabled device or an access port receives an 801.Q frame? |
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Definition
| The device ignores the tagged portion of the frame and switches the packet at layer 2 as if it were a standard ethernet frame. This allows for the placement of layer 2 intermediate devices, such as other switches and bridges, on the 801.1Q trunk line. |
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Term
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Definition
| Baby giants are frames that are larger than the standard MTU of 1500 bytes but less than 2000 bytes. Both ISL and 802.1Q increase the MTU beyond 1500 bytes, so both are considered baby giants. |
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Term
| What is the default native VLAN on a Cisco switch? |
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Definition
| The default VLAN is VLAN 1. Switches transmit any layer 2 frame from a native VLAN on the trunk port untagged. |
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Term
| What happens when the native VLAN is differnet on 2 devices? |
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Definition
| Misconfiguration of the native VLAN for 802.1 trunk ports on the same trunk link might cause layer 2 loops or black holes. |
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Term
| How does ISL handle unencapsulated frames received on a trunk port? |
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Definition
| ISL drops any unencapsulated frames that are received on a trunk port, and all frames that are transmitted from a trunk port are encapsulated, including the native VLAN. |
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Term
| How does the Port VLAN ID (PVID) parameter on a switch work with 802.1Q? |
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Definition
| Switches assign every 802.1Q port a PVID value based on its native VLAN ID (The default is VLAN 1). All switches assign all untagged frames to the VLAN that is specified in the PVID parameter. If a received frame is untagged, it is forwarded to the VLAN that is contained in the PVID. |
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Term
| Describe the use of Dynamic Trunking Protocol (DTP). |
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Definition
| Dynamic Trunking Protocol is a Cisco propreitary point-to-point protocol on trunk ports to negotiate the trunking state. DTP negotiates the operational mode of directly connected switch ports to a trunk port and selects an appropriate trunking protocol. Negotiaing trunking is a recommended practice in multilayer switched networks because it avoids network issues resulting from trunking misconfigurations. |
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Term
| What are the supported VLAN ranges for each of the 2 trunking protocols? |
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Definition
| ISL supports VLAN numbers inthe range of 1 to 1005, and 802.1Q VLAN numbers are in the range of 1 to 4094. |
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Term
| What is the default behavior of VLAN trunks with each of the 2 trunking protocols? |
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Definition
| The default behavior of VLAN trunks is to permit all normal and extended range VLANs across the link if it is an 802.1Q interface and to permit normal VLANs in the case of an ISL interface |
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Term
| What are the reasons that VLAN mappings are required when using both 802.1Q and ISL? |
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Definition
- When using both trunking protocols, 802.1Q VLANs in the range of 1 to 1000 are automatically mapped to the corresponding ISL VLAN. However, 802.1Q VLAN numbers greater than 1000 must be mapped to a ISL VLAN to be recognized and forwarded by Cisco network devices. - In a network with non-Cisco devices that use reserved VLANs, VLANs must be mapped to nonreserved to work in Cisco networks. |
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Term
| What are some restrictions when mapping 802.1Q VLANs to ISL VLANs? |
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Definition
- Limited to 8 802.1Q-to-ISL VLAN mappings on a switch. - Limited to mapping 802.1Q VLANs to Ethernet-type ISL VLANs. - It's important not to enter the native VLAN of any 802.1Q trunk in the mapping table to avoid overlapping numbers. - Mapping an 802.1Q VLAN to an ISL VLAN blocks the traffic on the 802.1Q VLAN corresponding to the mapped ISL VLAN. - VLAN mappings are local to each switch. Configure the same VLAN mappings on all appropriate switches in the network. |
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Term
| What tunneling feature allows a service provider to transport VLANs with VLANs, preserving individual customer's VLAN assignments without requiring them to be unique? |
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Definition
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Term
| Describe the different trunking modes supported by Cisco switches. |
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Definition
- Access - Puts the interface into permanent nontrunking mode and negotiates to convert the link into a nontrunk link. - Trunk - Put the interface into permanent trunking mode and negotiates to convert the link into a trunk link. - Noegotiate - Puts the interface into permanent trunking mode but prevents the interface from generating DTP frames. You must configure the neighboring interface manually as a trunk interface to establish a trunk link. - Dynamic desirable - Make the interface actively attempt to convert the link to a trunk link. The interface becomes a trunk interface if the neighboring interface is set to trunk, desirable, or auto mode. - Dynamic auto - Makes the interface willing to convert the link to a trunk link. The interface becomes a trunk interface if the neighboring interface is set to trunk or desirable mode. |
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Term
| What is the default trunking mode for a switch running IOS? CatOS? |
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Definition
| The default trunking port for a switch running ISO is dynamic desirable. For a switch running CatOS, its dynamic auto. |
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Term
| What command configures the encapsulation type on a trunk port? |
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Definition
| switchport trunk encapsulation {isl | dot1q | negotiate} |
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Term
| What command configures an interface as a layer 2 trunk? |
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Definition
| switchport mode {dynamic {auto | desirable} | trunk} |
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Term
| What command specifies the native VLAN? |
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Definition
| switchport trunk native vlan vlan-id |
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Term
| What command configures the allowable VLANs for a specific trunk? |
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Definition
| switchport trunk allowed vlan {add | except | all | remove} vlan-id... |
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Term
| What command configures the trunking mode and method using CatOS? |
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Definition
| set trunk mod/port [on | desirable | auto | nonegotiate] [isl | dot1q] |
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Term
| What command removes VLANs from a trunk using CatOS? |
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Definition
| clear trunk mod/port vlan IDs |
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Term
| What command tags all the VLANs including the native VLAN in 802.1Q using CatOS? |
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Definition
| set dot1q-all-tagged enable [all] |
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Term
| What command can be used to display the trunking information for a particular port using IOS? Using CatOS? |
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Definition
For IOS: show interfaces interface-type mod/port trunk For CatOS: show trunk [mod\port] |
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Term
| When troubleshooting a problem with a trunk port, what configurations do you need to verify? |
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Definition
- Interface modes - Native VLAN - Encapsulation types |
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Term
| At what layer does VTP work at? |
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Definition
| VTP is a layer 2 messaging protocol that maintains VLAN configuration consistancy by managing the additions, deletions, and name changes of VLANs within a VTP domain. |
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Term
| VTP can operate in which modes? |
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Definition
VTP operates in server, client, transparent or off mode (off mode is only available in CatOS).
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Term
| Which VTP mode is currently only supported in Cisco CatOS? |
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Definition
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Term
| What is the default VTP mode for a Catalyst switch? |
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Definition
| Server mode, but Catalyst switches do not propagate VTP information out trunk interfaces until a mangement domain name is specified or learned. |
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Term
| How ofter does a switch flood the domain with VTP messages? |
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Definition
| Every 5 minutes or whenever there is a change in VLAN configurations. Cisco switches transmit VTP advertisements over the management VLAN using a layer 2 multicast frame. |
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Term
| What is the configuration revision number of a switch in VTP-transparent mode? |
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Definition
| A switch in VTP-transparent mode always has the configuration reversion number of 0 |
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Term
| What is the recommended implementation on a network when running 2 or more different versions of VTP? |
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Definition
| Its recommended that only one VTP version be used for network stability, because each version it not interoperable with another. |
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Term
| What are some features that are supported in VTPv2 that are not implemented in VTPv1? |
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Definition
- Token Ring support - VTPv2 supports Token Ring LAN switching and Token Ring VLANs - Unrecognized Type-Length-Value (TLV) support - A VTPv2 server or client propagates configuration changes to its other trunks even for TLVs that it cannot parse. - Version-independent transparent mode - VTPv2 forwards VTP messages in transparent mode, without checking the version (unlike VTPv1) - Consistency checks - VTPv2 preforms VLAN consistency checks (such as VLAN names and values) only when you enter new information through the CLI or via SNMP. But it does not check new information obtained from a VTP message or when read from NVRAM. |
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Term
| In what versions of CatOS and IOS is VTP version 3 supported? |
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Definition
| VTPv3 is supported in CatOS version 8.1 and above, and is not currently available for Cisco IOS. |
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Term
| What are some enhancements in VTPv3 over the previous versions? |
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Definition
- Support for extended VLANs (1025 to 4094) - Support for the creation and advertising of pVLANs - Improved server authentication - Interaction with VTP versions 1 and 2 - Configurable on a per-port basis |
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Term
| Using VTPv3, where can you modify the VTP configuration? |
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Definition
| The primary server is the sole server in a VTP domain that is used to modify VTP configuration. A VTP domain may operate without an active primary server because the secondary servers ensure presistence of the configuration over reloads. |
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Term
| What command is used to change a switch to a primary server when using VTPv3? |
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Definition
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Term
| What happens to all other potential primary servers in a domain when a switch is changed to the primary server using VTPv3? |
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Definition
| All other potential primary servers in the domain resign to secondary server mode to ensure that only one primary sever exists in the VTP domain at any given time. |
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Term
| How does VTPv3 work with previous versions? |
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Definition
| A switch that is running VTPv3 does not accept a configuration from VTP sersion 1 or 2 neighbors. It is recommended that you change all the modes of the switches that are running VTPv1 and 2 to VTP clients and reset their respective VTP reversion versions. |
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Term
| What is the default VTP mode for a Cisco Catalyst switch? |
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Definition
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Term
| What's different on VTPv3 than VTPv1 and 2 in regards to pruning? |
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Definition
| Enabling or disabling VTP pruning with VTPv1 and 2 on a VTP server propagates the change throughout the management domain. But in VTPv3, VTP pruning must be enabled manually on each switch. |
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Term
| What command configures the VTP mode on a switch running IOS? Running CatOS |
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Definition
For IOS: vtp mode {server | client | transparent} For CatOS: set vtp mode {server | client | transparent | off}
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Term
| What command sets the VTP domain name using IOS? Using CatOS? |
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Definition
For IOS: vtp domain domain_name For CatOS: set vtp domain domain_name |
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Term
| What command sets the VTP version using IOS? Using CatOS? |
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Definition
For IOS: vtp version {1 | 2} For CatOS: set vtp version {1 | 2} |
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Term
| What command enables VTP pruning using IOS? Using CatOS? |
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Definition
For IOS: vtp pruning For CatOS: set vtp pruning enable |
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Term
| What command displays information about the VTP configuration and current state using IOS? Using CatOS? |
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Definition
For IOS: show vtp status For CatOS: show vtp domain |
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Term
| What command displays statistics about VTP operation? |
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Definition
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Term
| What command enables spanning-tree portfast and turns off channeling on an interface? |
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Definition
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