Ethernet, VLANs, and Spanning Tree Protocol Flashcards
Which switch port setting will be automatically detected even if auto-negotiation is disabled? What does it use to do this?
Speed. The switch uses the incoming electrical signal.
What Cisco switch feature automatically detects crossover and straight-through cables and swaps the pairs its ports use so copper Ethernet works properly?
Auto-MDIX
Officially, automatic medium-dependent interface crossover
What function in auto-negotiation does a switch use to determine port speed?
Fast Link Pulses
How does a switch choose a duplex setting if auto-negotiation is disabled?
It uses the default setting for the port speed.
What is the default duplex setting for:
A) 10BaseT
B) 100BaseT
C) 1000BaseT
A) half
B) half
C) full
How can you disable switch port auto-negotiation?
Statically configure the port speed and duplex.
What Ethernet port setting uses loopback circuitry?
Half duplex
When configuring speed and duplex manually, which must be set first?
Speed
Name the two most common forms of Ethernet framing.
Ethernet V2 and 802.3.
How can an Ethernet V2 frame indicate the protocol contained within it?
Via its Type field.
What are the two ways an 802.3 Ethernet frame can signal what type of traffic is contained within it?
An 802.2 (or LLC) field or a SNAP header with a Type field.
What does 802.2 use to announce the traffic type contained within the Ethernet frame?
An SSAP and a DSAP.
What makes the bits in an Ethernet address byte different from the rest of the Ethernet frame? Name two terms for this bit setup.
The bits move right-to-left in order of significance. This is called canonical or little-endian.
What is the 8th bit in the first byte of an Ethernet address used for? What’s the term for it?
It’s used to identify the address as unicast (0) or multicast (1). It’s called the I/G bit.
What’s the 7th bit in the first byte of an Ethernet address used for? What’s the term for it?
It identifies whether the address is assigned by the hardware vendor (0) or whether it’s been set by an administrator (1). The term is U/L, for Universal/Local.
What’s the OUI for an Ethernet multicast address?
0x01005E
Give the length of a SNAP header and the 802.2 DSAP that signifies it’s there.
2 bytes; 0xAA
What’s the IEEE designation for Fast Ethernet?
802.3u
What’s the IEEE designation for GigE over fiber?
802.3z
What’s the IEEE designation for GigE over copper?
802.3ab
What command displays the Ethernet addresses known to a switch?
Switch> show mac address-table
Give the maximum distance for 1000BaseLX in each of MM and SM.
MM 3 km, SM 10 km
Give the maximum distance for 1000BaseSX in each of 62.5-micron and 50-micron fiber.
62.5-micron 220 m, 50-micron 550m
Give the maximum length of 1000BaseZX.
100 km
What’s the best practice with respect to VLANs and IP addressing?
Maintain a one-to-one relationship between VLANs and IP subnets.
What are the three tasks one can perform in VLAN configuration mode?
- Create VLANs
- Set basic administration parameters
- Verify VTP configuration
What VLANs can be configured in VLAN configuration mode?
Normal-range VLANs (1-1005)
Where is the VLAN database stored? What’s the filename?
Flash; vlan.dat
Give the VLAN configuration mode commands that:
- Display the VLANs that are actively configured on the switch.
- Display the VLANs that will be in place after configuration changes are finalized.
- show current
2. show proposed
Give the VLAN configuration mode commands that:
- Implement the proposed configuration without leaving VLAN configuration mode.
- Cancel changes and leave VLAN configuration mode.
- Cancel the changes and stay in VLAN configuration mode.
- apply
- abort
- reset
Give the VLAN configuration database command that creates VLAN #15 and titles it cisco.
vlan 15 name cisco
Give the command that can be used in interface configuration mode to create VLAN 15 and assign it to the interface.
(config-if)# switchport access vlan 15
What distinguishes a primary VLAN from a secondary VLAN in a private VLAN?
The primary VLAN is promiscuous; its members can talk to any other member of the private VLAN. Members of a secondary VLAN can talk to each other and to members of the primary VLAN.
Name and briefly describe the two types of secondary VLANs.
Community VLANs have multiple members that talk to each other.
Isolated VLANs have a single member that can only communicate with members of the primary VLAN.
Name the three items that VTP advertises about a VLAN.
- VLAN ID
- VLAN name
- VLAN type (Ethernet, Token Ring, etc.)
What VTP mode(s) issue(s) advertisements?
Server and client
What VTP mode(s) forward(s) received VTP advertisements?
Server, client, and transparent
What VTP mode(s) allow(s) you to create or modify VLANs using configuration commands?
Server and transparent
How does a VTP domain track changes to try to ensure that the most current configuration is on each switch?
It uses VTP revision numbers.
What is the default VTP mode on a switch?
Server
What causes a switch to start sending VTP updates?
When the VTP domain name is set.
How could a switch configured as a VTP client inadvertently get the wrong VTP information?
It could receive a VTP announcement from the wrong domain first. VTP clients adopt the first VTP domain name they see.
A VTP domain should have at least how many VTP servers?
2
Where do VTP servers store their vlan.dat files? How about VTP clients?
Both store the files in flash. (Depending on the model, some can store vlan.dat in NVRAM, too)
How can you prevent DoS attacks via VTP?
Set a VTP password.
What encryption do VTP passwords use?
MD5
Give the command that sets a switch’s VTP mode to transparent.
(config)# vtp mode transparent
Give the commands that define a switch’s VTP domain as CCIE-domain and the password as CCIE.
(config) # vtp domain CCIE-domain
(config) # vtp password CCIE
True or False: VTP domain names are case-sensitive.
True
What is the range of normal VLAN numbers?
1-1001
What is the extended range of VLAN numbers?
1006-4094
What VLAN number is reserved and cannot be used?
0
What VLAN number range(s) can be pruned by VTP?
2-1001
these are also the VLANs that can be advertised
Which VLAN mode(s) can use extended VLANs?
VTP transparent mode
Where does a switch in VTP transparent mode store extended-range VLAN configuration commands?
Running configuration only
Which VLAN identification method(s) support(s) extended-range VLANs?
Both ISL and 802.1Q
Which VLAN identification method(s) support(s) the concept of a native VLAN?
802.1Q only
What concept does ISL use to support trunking?
Encapsulation–it puts a new header around data.
By how much does ISL increase the size of an Ethernet frame?
26 bytes (the size of the header)
Looking at a frame on an ISL-trunked link, how could you determine that the frame is using ISL?
The frame has a source MAC of the device performing the trunking and a destination MAC of 0100.0C00.0000 or 0300.0C00.0000.
Where does a switch in VTP transparent mode store normal-range VLAN information?
In both vlan.dat (Flash) and running configuration.
How many bytes does 802.1Q add to an Ethernet frame?
4
How does 802.1Q signal to devices that a tag exists?
The first two bytes of the tag are an EtherType of 0x8100.
How does the native VLAN option in 802.1Q add resiliency to an Ethernet network?
It allows the switch to attempt to continue sending data on the native VLAN even if trunking fails.
What is the default DTP mode?
Desirable
Give the commands that display:
- A summary of trunk-related information
- Trunking details for interface g0/0
- Nontrunking details for interface g0/0
- show interface trunk
- show interface g0/0 trunk
- show interface g0/0 switchport
What command allows you to administratively forbid VLANs from existing over a trunk?
switchport trunk allowed
What two conditions must be present for a VLAN to be active on a trunk?
It must be allowed on the trunk and configured on the switch.
Give the interface configuration commands that tell the switch to do the following:
- Always trunk on this end; send DTP to inform the other side.
- Don’t send DTP messages.
- Initiate DTP conversations and trunk if negotiation succeeds.
- Listen for DTP and trunk if negotiation succeeds.
- switchport mode trunk
- switchport nonegotiate
- switchport mode dynamic desirable
- switchport mode dynamic auto
How can routers learn about trunking interfaces?
Via manual configuration–there’s no DTP support.
Give the command that you’d put on a router sub-interface to indicate that VLAN 201, the VLAN for this sub-interface, is the 802.1Q native VLAN.
(config-subif)# encapsulation dot1q 201 native
True or False: VTP can pass over a Q-in-Q service, but CDP cannot.
False–both can pass over Q-in-Q.
Give the three parts of the STP bridge ID in later STP implementations like PVST+ and MST. Give the length of each.
Priority: 4 bits
System ID Extension (VLAN ID): 12 bits
System ID (MAC Address): 48 bits
What four fields does a switch update in a Hello BPDU from the root bridge before forwarding it out to neighbors?
Cost
Bridge ID (puts its own ID in the BPDU)
Port priority
Port number
True or False: Bridges forward Hello BPDUs out ports they are blocking so other bridges know they are a potential future path to the root.
False
List the four items a switch uses to choose its root port by order of relevance.
- Cost
- Lowest forwarding bridge ID
- Lowest port priority from the forwarding bridge
- Lowest port number from the forwarding bridge
What’s the default port priority? How about the range?
- Range is 0-240 by 16s.
How is the designated port for a segment determined?
Cost, bridge ID, port priority, port number (same as root port)
What are the default STP Hello and Maxage timers?
2 seconds and 20 seconds (Maxage is 10x Hello)
Under what circumstance does a switch not have to wait for the Maxage timer to expire to declare a link down?
When the link is a failed port channel.
Give the revised IEEE and 802.1t STP costs, respectively, for the following Ethernet speeds:
- 10 Mbps
- 100 Mbps
- 1 Gbps
- 10 Gbps
- 100; 2,000,000
- 19; 200,000
- 4; 20,000
- 2; 2,000
What will a switch that experiences a topology change do? What will other switches do to help out?
The switch will send a Topology Change Notification BPDU out its root port. Switches upstream forward the TCN toward the root and send back Hellos with the TCA bit marked.
How does a root bridge respond to an advertised change in topology?
It sends Hellos marked with TCAs out all ports, ensuring that all switches in the network learn that there has been a topology change.
How will a switch that receives a Hello BPDU marked with the TCA bit change its behavior?
It will use the Forward Delay timer to age out CAM entries.
What is the default for the STP Forward Delay timer?
15 seconds
What are the transitory STP states?
Listening and Learning
How does PVST+ differ from traditional STP?
It allows for a different root bridge and blocking interfaces per VLAN.
How does PVST+ treat non-Cisco switches in an 802.1Q environment? What happens in the non-Cisco switches?
It views them as a single link over to Cisco switches on the other side. The non-Cisco switches have a Common Spanning Tree for all VLANs.
How do Cisco switches communicate PVST+ information across a non-Cisco switching domain?
They set their BPDUs with the multicast destination of 0100.0CCC.CCCD, which the non-Cisco switches see as standard multicast and forward to the other side.
Give the switch command that tells you details about the root bridge. What information in the output of this command would tell you that you’re looking at the root bridge?
show spanning-tree root
You’re looking at the root bridge if the cost listed is 0.
What’s the difference between the STP Listening and Learning states?
During the Learning state, the switch learns MAC addresses from received frames.
