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CCNP Switch Practice > Key Topic Review > Flashcards

Key Topic Review Flashcards

1
Q

Collision Domain

A

A network segment where packets can collide

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2
Q

Discuss flooding and unknown unicast flooding

A

Flooding - sending a frame out all ports
Unknown Unicast Flooding - Received a packet with a destination MAC that is unknown to the switch so it floods it out all ports except originator

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3
Q

Describe togology based switching

A

Layer 3 routing information builds and populates a single database of the entire network topology. The database is consulted for forwarding. The longest match found is used as the layer 3 destination.

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4
Q

Describe the CAM (Content Addressable Memory) table

A

As frames arrive on ports MAC addresses added to CAM table with MAC correspondant to receiving port. VLAN and timestamp also added.

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5
Q

Explain TCAM (Ternary Content-Addressable Memory)

A

TCAM values are composed of value, mask, and result combinations. Fields from frame or packet headers are fed into the TCAM, where they are matched against the value and mask pairs to yield a result.

Values - 134-bit quantities, consisting of source and destination addresses and other relevant protocol information

Masks - 134-bit quantities, in exactly the same format, or bit order, as the values. Masks select only the value bits of interest.

Results - Numeric values that represent what action to take after the TCAM lookup occurs.

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6
Q

Discuss the properties of Ethernet switching.

A

Addresses the problems of collisions by reducing the number of users connected to an Ethernet segment. Typically allows for full duplex with only once device connected to either end of the cable.

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7
Q

Explain Ethernet auto negotiation.

A

The link speed is determined by electrical signaling so that either end of a link can determine what speed the other end is trying to use. If both ends of the link are configured to autonegotiate, they will use the highest speed that is common to them.

A link’s duplex mode, however, is negotiated through an exchange of information. This means that for one end to successfully autonegotiate the duplex mode, the other end also must be set to autonegotiate. Otherwise, one end never will see duplex information from the other end and won’t be capable of determining the correct mode to use. If duplex autonegotiation fails, a switch port always falls back to its default setting: half duplex.

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8
Q

Discuss the similarities and differences between Ethernet types.

A

Similarities
-Scale speed by using the same IEEE 802.3 frame format

Differences

  • Physical layer has been modified to increase data-transmission speeds.
  • Merged IEEE 802.3 standard and the ANSI X3T11 FibreChannel standard to gain speed.
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9
Q

Describe 10-Gigabit Ethernet

A
  • Differs only at the physical layer
  • Only operates at full duplex

Two classifications of transceivers that can be used as Physical Media Dependent (PMD) interfaces

LAN PHY-Interconnects switches in a campus network, predominantly in the core layer
WAN PHY-Interfaces with existing synchronous optical network (SONET) or synchronous digital hierarchy (SDH) network typically found in metropolitan-area network.

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10
Q

Explain VLAN characteristics

A

A single broadcast domain.

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11
Q

Discuss how to create a VLAN

A
  • VLAN must be created on a switch
  • Must be assigned to specific ports
  • VLANs 1002 through 1005 for special use
  • Default range 1 to 1001 and 1 to 4094 with extended VLANs
  • Extended range only works in transparent mode
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12
Q

Discuss planning strategies for VLAN implementation and the two types of VLANs

A

Things to consider: traffic patterns, application types, segmentation of common workgroups, and network-management requirements.

Cisco recommends a one-to-one correspondence between VLANs and IP subnets. VLANs sholud not extend beyond the layer 2 domain of the distribution switch. IE should not straddle the core.

End-to-End VLANs (aka campuswide VLANs) span the entire switch fabric of a network. Users maintain VLAN regardless of physical location.

Local VLANs-In today’s world most users follow the 20/80 rule. These VLANs group users based on geographic location.

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13
Q

Explain 802.1Q Trunking

A

Used to carry VLAN associations over trunk links. 802.1Q does not perform encapsulation like ISL. It embeds tagging information within the layer 2 frame. Introduces concept of native VLAN (defaults to 1).

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14
Q

Dynamic Trunking Protocol (DTP) and VLAN trunk configuration

A

Used to autonegotiate trunking protocol. Default setting is negotiate. Favors ISL if both sides support it. Trunks can be configured to determine which VLANs they will trunk. Trunk switchports can be set to any of the below three settings:

Trunk - This setting places the port in permanent trunking mode. DTP is still operational so if the far-end switch port is configured to trunk, dynamic desirable or dynamic auto mode, trunking will negotiate successfully.

Dynamic Desirable (the default) - The port actively attempts to convert the link into trunking mode. Will successfully negotiate with any of the three settings.

Dynamic Auto - The port can be converted into a trunk link, but only if the far-end switch actively requests it. If both ends are set to dynamic auto the trunk will not come up.

Use switchport nonegotiate to disable DTP

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15
Q

What must be agreeable on both ends before a trunk can be enabled?

A

Trunking mode (IE can’t both be auto), trunk encapsulation, native VLAN (trunk will come up, but with errors), and allowed VLANs (will come up as trunk, but VLANs discontinuous)

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16
Q

How is port duplex mode configured?

A

Ports operate either in half-duplex, full-duplex, or autonegotiated mode. Autonegotiation is only performed over UTP fast ethernet and gigabit ethernet ports. Autonegotiation works by attempting full-duplex operation first and half if full is unsuccessful.

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17
Q

FastEthernet1/0/1 is up, line protocol is up

What do the two ups refer to respectively?

A

The first up tells the state of the port’s physical or data link layer. If this is down, the link is physically disconnected or a link cannot be detected.

The second up shows the layer 2 status. If the state is given as errdisable the switch has detected a serious error condition on this port and has automatically disabled it.

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18
Q

How do you detect duplex mismatches?

A

Use the show interface command and look for error counts greater than 0. You may also notice a high runt count.

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19
Q

Describe the VTP modes

A

Server mode - VTP servers have full control over VLAN creation and modification for their domains. This is the default switch state.

Client Mode - VTP clients do not allow the administrator to create, change, or delete any VLANs. They will listen and modify configs based on advertisements from other switches. Will forward.

Transparent Mode - Will not participate in VTP. In version 1 they will not relay VTP information to other switches unless the VTP domain names and version match. In version 2 they will relay all VTP information out their trunks.

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20
Q

Explain VTP configuration revision number

A

Configuration revision number used to keep track of the most recent information. Every switch in the VTP domain stores the most recent revision number received. Always defaults to 0. VTP servers will push version number out if not already configured on other switches (and they are version 2 capable).

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21
Q

Explain VTP synchronization problem

A

If a switch is introduced in VTP sever mode with a high revision number it will override the settings on all other switches. For critical portions of the network consider using VTP transparent mode to prevent the issue.

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22
Q

How can you verify VTP settings?

A

show vtp status

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23
Q

What is VTP pruning?

A

VTP pruning makes more efficient use of trunk bandwidth by reducing unnecessary flooded traffic. Broadcast and unknown unicast frames on a VLAN are forwarded over a trunk link only if the switch on the receiving end of the trunk has ports in that VLAN.

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24
Q

Describe EtherChannel bundling

A

Two to eight links of the same type can be bundled together for use in their aggregate bandwidth.

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25
Q

Explain how traffic is distributed in EtherChannel

A

Frames are forwarded dependent on a hashing algorithm. Hashing algorithm can be based on IP address, destination IP address, combo of src and dest IP addresses, source and destination MAC addresses, or TCP/UDP port numbers.

The switch hashes based on the number of ports grouped into the EtherChannel. If two ports are bundled together a 1 bit index is required. Either the lowest-order address bit or the XOR of the last bit of the addresses in the frame is used as the index.

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26
Q

Describe Port Aggregation Protocol (PAgP)

A

PAgP packets are exchanged between switches over EtherChannel-capable ports.

Ports that have the same neighbor device ID and port group capability are bundled together as a bidirectional, point-to-point EtherChannel link.

PAgP forms an EtherChannel only on ports that are configured for either identical static VLANs or trunking.

PAgP can be configured in active mode (desirable), in which a switch actively asks a far-end switch to negotiate an EtherChannel, or in passive mode, in which a switch negotiates an EtherChannel only if the far end initiates it.

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27
Q

Link Aggregation Control Protocol

A

LACP also identifies neighbor (like PAgP). It also assigns switches on either end roles.

The switch with the lowest system priority (2-byte priority value followed by MAC) is allowed to make decisions about what ports actively are participating in EtherChannel at any given time.

Ports contain port priority (2 byte priority and 2 byte port number). Up to 8 ports may be active at any given time.

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28
Q

Describe PAcP configuration (specifically silent submode)

A

By default PAgP operates in silent submode with the desirable and auto modes, and allows ports to be added to an EtherChannel even if the other end of the link is silent and never transmits PAgP packets. If no packets are received from the other end PAgP assumes the channel should be built anyway. If you want to ensure traffic is sent use the non-silent subcommand. If PAgP isn’t heard on a port than PAgP reports to spanning tree that the port is down.

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29
Q

Describe LACP configuration

A

Contains modes on, passive and active.

Each interface included in a single EtherChannel bundle must be assigned to the same unique channel group number.

Can contain standby interfaces.

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30
Q

List some troubleshooting techniques for EtherChannel.

A

EtherChannel on mode does not send or receive PAgP or LACP packets. Therefore, both ends should be set to on mode before the channel can form.

EtherChannel desirable (PAgP) or active (LACP) mode attempts to ask the far end to bring up a channel. Therefore, the other end must be set to either desirable or auto mode.

EtherChannel auto (PAgP) or passive (LACP) mode participates in the channel protocol, but only if the far end asks for participation. Therefore, two switches in the auto or passive mode will not form an EtherChannel.

PAgP desirable and auto modes default to the silent submode, in which no PAgP packets are expected from the far end. If ports are set to nonsilent submode, PAgP packets must be received before a channel will form.

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31
Q

Describe transparent bridge operation.

A

Listens for frames and learns their source.

Uses destination to determine what port to send frame out.

Floods broadcast and unknown unicast

The bridging process must be effectively transparent

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32
Q

Explain a bridging loop

A

See page 130

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33
Q

Describe BPDUs (Bridge Protocol Data Unit)

A

Two types:

Configuration BPDU: Used for spanning tree configuration

Topology Change Notification (TCN) BPDU: Used to announce changes in the network topology

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34
Q

Describe Root Bridge Election

A

Each switch has a unique bridge ID made up of a 2 byte bridge priority that defaults to 32,768 followed by the 6 byte MAC address.

Each switch after bootup first sends out BPDUs to other switches listing itself as the root bridge.

If a switch hears a better (in this case lower) advertisement, it sets that switch as the root

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35
Q

Explain root port selection and root port cost

A

Port cost is set based on the bandwidth of a link.

Cost is whatever is the advertised cost plus the cost of the incoming port. These are the advertisements sent out. The lowest cost path becomes the root port.

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36
Q

How is a designated port selected?

A

Lowest cost on a single ethernet segment. Based on the following in order:

1) Lowest root bridge ID
2) Lowest root path cost to root bridge
3) Lowest sender bridge ID
4) Lowest sender port ID

The ports on the segment that aren’t the designated port enter into blocking mode.

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37
Q

Explain STP port states

A

Disabled: Ports that are administratively shut down

Blocking: Ports cannot receive or transmit data or add MAC addresses to the table. Can receive BPDUs

Listening: Allowed to send and receive BPDUs. May become a root port or designated port. Will return to blocking if it loses status. Lasts for forwardDelay seconds.

Learning: Port sends and receives BPDUs and can learn MAC addresses. Also lasts forwardDelay seconds.

Forwarding: Fully functioning port. Typically belongs to an end user connection.

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38
Q

Explain the three STP timers

A

Hello Time: Time between configuration BPDUs send by the root bridge. Root bridge sets hello time. Default is 2 seconds.

Forward Delay: The time interval that a switch port spends in both the listening and learning states. Default is 15 seconds.

Max Age: The time interval that a switch stores a BPDU before discarding it. Assumes topology change if Max Age reached without hearing a hello. Default is 20 seconds.

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39
Q

Describe a topology change

A

A topology change occurs when a switch either moves a port into the forwarding state or moves a port from the forwarding or learning state to the blocking state. The switch sends a TCN BPDU out its root port so that the root bridge receives news of the topology change.

Continues sending TCN BPDUs every Hello Time interval until an ack is received.

Eventually the root bridge hears the notification and sends out an ack and sends a configuration BPDU with the topology change flag set causing each switch to shorten their aging times to the forward delay value down from a default of 300 seconds.

40
Q

Describe common spanning tree

A

IEEE 802.1Q specification for STP. One instance of spanning tree for all VLANs. No capability for load balancing.

41
Q

Per-VLAN spanning tree

A

Allows one instance of spanning tree per VLAN. PVST+ effectively supports switches running PVST, PVST+, and CST in the same network.

42
Q

Explain the pitfalls of root bridge election

A

If defaults are left in place, there is no guarentee that the slowest switch might not accidentally become the root bridge.

No clear backup is created if all defaults are left.

Location of root bridge may be inadequate.

43
Q

What are some best practices for placing the root bridge?

A

Configure one switch as a root bridge in a determined fashion.

Configure another switch as a secondary root bridge, in case of primary root bridge failure.

44
Q

Recall the difference between standard system IDs and extended system IDs in spanning tree protocol
(Chapter 8)

A

Both default to 32,768 however, extended must be multiples of 4096. 0 is valid.

Command is spanning-tree vlan vlan-list priority bridge-priority

45
Q

What is port fast? (Chapter 8)

A

Enables fast connectivity to be established on access-layer switch ports to workstations that are booting. Changes the listening and learning states to a negligable amount of time.

46
Q

What is uplinkfast? (Chapter 8)

A

Sets a potential designated or root port to blocking on a leaf node. The moment the root port fails it brings up the secondary link without waiting.

47
Q

What is backbone fast? (Chapter 8)

A

Short circuits the max age timer. If an indirect link failure is detected actively seeks to bring up a port before the max-age timer expires. Still must go through forward delay on listening and learning.

48
Q

What is root guard? (Chapter 9)

A

The root guard ensures that the port on which root guard is enabled is the designated port. Normally, root bridge ports are all designated ports, unless two or more ports of the root bridge are connected together. If the bridge receives superior STP Bridge Protocol Data Units (BPDUs) on a root guard-enabled port, root guard moves this port to a root-inconsistent STP state. This root-inconsistent state is effectively equal to a listening state. No traffic is forwarded across this port. In this way, the root guard enforces the position of the root bridge.

Simple Version: This port can’t become a root port.

Returns to normal state when the port stops hearing superior BPDUs. Affects all VLANs!

49
Q

Describe BPDU Guard. (Chapter 9)

A

If any BPDU is received on a port where BPDU Guard is enabled, that port immediately is put into the errdisable state.

50
Q

Describe loop guard (Chapter 9)

A

When enabled, keeps track of the BPDU activity on nondesignated ports. While BPDUs are received, the port is allowed to behave normally. When BPDUs go missing the port is moved to a loop inconsistent state. Works on a per-VLAN basis.

51
Q

Describe Unidirectional Link Detection (UDLD) (Chapter 9)

A

Monitors the link to see if it is truly bidirectional. A switch sends special layer 2 UDLD frames identifying its switch port at regular intervals. Expects far end to echo.

Two modes:

Normal Mode: Only marks port with as having undetermined state and logs to syslog on failure.

Aggressive Mode: Places in errdisable state if failure is detected.

52
Q

Describe BPDU filtering (Chapter 9)

A

Prevents BPDUs from being processed on a port and effectively disables STP on that port.

53
Q

What are the port roles in Rapid Spanning Tree Protocol (802.1w)? (chapter 10)

A

Root Port: The one switch port on each switch that has the best root path cost to root.

Designated Port: The switch port on a network segment that has the best root path cost to the root.

Alternate Port: A port that has an alternative path to the root, different from the path the root port takes. This path is less desirable than the root path.

Backup Port: A port that provides a redundant, but less desirable, connection to a segment where another switch port already connects.

54
Q

What are the port states in RSTP (802.1w)?

A

Discarding: Incoming frames are dropped and no MAC addresses are learned. Combines 802.1d disabled, blocking, and listening states.

Learning: Incoming frames are dropped, but MAC addresses are learned.

Forwarding: Incoming frames are forwarded according to MAC addresses that have been learned.

55
Q

Describe RSTP compatability.

A

RSTP (802.1w) BPDUs are distinguished from 802.1D BPDUs by the version number in the BPDU. RSTP can coexist with 802.1D. If a version 0 BPDU is detected on a port that port operates by 802.1D rules.

56
Q

What are the port types in RSTP (802.1W)?

A

Edge Port: A port at the edge of the network, where only a single host connects.

Root Port: The port that has the best cost to the root of the STP instance.

Point-to-point port: Any port that connects to another switch and becomes a designated port. This port is designated by a handshake process where one switch proposes that its port becomes the designated port and the other side must agree.

57
Q

Describe RSTP synchronization.

A

For each nonedge port, the switch exchanges a proposal-agreement handshake to decide the state of each end of the link. Each switch assumes it should become the designated port for the segment and sends a proposal suggesting this.

Before agreement the inferior switch moves all nonedge ports to discarding.

The sender with the superior BPDU becomes the designated port. The switch with the inferior BPDU responds with an agreement message and moves the root port to the forwarding state. The sender’s designated port also begins forwarding.

For each non-edge port in the discarding state a new proposal message is sent.

58
Q

How does RSTP (802.1w) detect a topology change?

A

RSTP detects a topology change only when a nonedge port transitions to the Forwarding state. BPDUs, with their topology change bit set, are sent out all the nonedge designated ports. This is done until the TC timer expires, after two intervals ofteh hello time.

59
Q

How do you configure an RSTP edge port?

A

By enabling portfast. (spanning-tree portfast)

60
Q

How do you enable global RPVST+ mode?

A

spanning-tree mode rapid-pvst

61
Q

Describe multiple spanning tree (MST)

A

MST can work with 802.1Q and PVST+. Organized into MST regions. For regions to be interoperable the following must occur:

MST configuration name (32 characters)
MST configuration revision number (0 to 65535)
MST instance-to-VLAN mapping table (4096)

62
Q

Explain IST instances.

A

Within a single MST region, an Internal Spanning Tree (IST) runs to work out a loop-free topology between the links where CST meets the region boundary and all switches inside the region. Think of the IST instance as locally significant CST, bounded by the edges of the region.

IST presents the entire region as a single virtual bridge to the outside.

63
Q

Describe IST instances

A

Inside a region, the actual MST instances (MSTI) exist alongside the IST. Cisco supports a maximum of 16 MSTIs in each region with IST always being MSTI 0 leaving 1-15 for use.

64
Q

Describe interVLAN routing (chapter 11)

A

VLANs must be transported by a layer 3 device

65
Q

Describe a switched virtual interface (SVI)

A

A logical interface that represents an entire VLAN.

66
Q

Discuss the Forwarding Information Base and its contents

A

Contains subnets in order of specificity from most specific to least specific. When a switch receives a packet it can examine the destination address and find the longest match.

67
Q

Describe the Forwarding Information Base adjacency table

A

Recall that the FIB keeps the Layer 3 next-hop address for each entry. To streamline packet forwarding even more, the FIB has corresponding Layer 2 information for every next-hop entry. This portion of the FIB is called the adjacency table, consisting of the MAC addresses of nodes that can be reached in a single Layer 2 hop.

68
Q

Explain the DHCP address negotiation process.

A

Client sends a broadcast DHCP discover message with its MAC address.

Server replies with DHCP offer containing IP address, subnet mask, default gateway, and some parameters for using the IP address.

Client sends a DHCP request formally requesting the offered address.

The DHCP server responds with a DHCP ACK message.

69
Q

How do you configure a DHCP relay?

A

Configure a layer 3 interface that joins the same VLAN as the client machines. This interface can be the default gateway for the clients and can act as a DHCP relay. Next use the ip helper-address command to identify the IP address of the actual DHCP server.

70
Q

Describe the design principles of the cisco hierarchical model

A

Cisco has refined a hierarchical approach to network design that enables network designers to organize the network into distinct layers of devices. The resulting network is efficient, intelligent, scalable, and easily managed.

71
Q

Describe the access layer

A

Access switches usually provide layer 2 vlan connectivity between users. Devices in this layer should have the following capabilities:

Low cost per switch port
High port density
Scalable uplinks to higher layers
User access functions such as VLAN membership, traffic and protocol filtering, and quality of service (QoS)
Resiliency through multiple uplinks
72
Q

Describe the distriubution layer

A

The distribution layer provides interconnection between the campus network’s access and core layers. Devices in this layer should have the following capabalities:

Aggregation of mulitple access-layer devices
High layer 3 throughput for packet handling
Security and policy-based connectivity functions through access lists or packet filters
QoS features
Scalable and resilient high-speed links to the core and access layers

73
Q

Core Layer

A

A campus network’s core layer provides connectivity of all distribution-layer devices. Core devices should have the following attributes:

Very high throughput at Layer 3
No costly or unnecessary packet manipulations (access lists, packet filtering)
Redundancy and resilience for high availability
Advanced QoS functions

74
Q

Describe a switch block

A

Recall how a campus network is divided into access, distribution, and core layers. The switch block contains switching devices from the access and distribution layers. All switch blocks then connect into the core block, providing end-to-end connectivity across the campus.

75
Q

Discuss the pitfalls of allowing a VLAN to span multiple access layer switches.

A

The switch block becomes fully dependent on spanning-tree convergence to keep the connections loop free. RSTP should be used on all the switches to improve the convergence time.

The link between the two distribution switches must be a layer 2 link. The access VLAN must extend across this link so that users on either access switch can reach the layer 3 gateway.

76
Q

Discuss two best practice designs for switch block redundancy.

A

All layer 2 connectivity should be contained within the access layer. The distribution layer should only have layer 3 links.

See page 260 for design pictures.

Design 1
No dependence on STP convergence; each VLAN extends to the distribution switches, but no further. Therefore, the STP topology is always converged.

A layer 3 link is needed between the distribution switches to carry routing updates.

Design 2
Requires layer 3 capable access switches.

No dependence on STP convergence; each VLAN extends to the distribution switches, but no further. Therefore, the STP topology is always converged.

Layer 3 links between the access and distribution switches carry routing updates. Network stability is offered through the fast convergence of the routing protocol.

77
Q

Explain a collapsed core design

A

A collapsed core block is one in which the hierarchy’s core layer is collapsed into the distribution layer. Here, both distribution and core functions are provided within the same switch devices.

See page 261 for pictures

78
Q

Explain a dual core design

A

A dual core connects two or more switch blocks in a redundant fashion. Although the collapsed core can connect two switch blocks with some redundancy, the core is not scalable when more switch blocks are added.

See page 263 for pictures

79
Q

Explain HSRP active and standby routers

A

Each of the routers that provides redundancy for a given gateway address is assigned to a common HSRP group. One router is elected as the primary, or active, HSRP router; another is elected as the standby HSRP router; and all the others remain in the listen HSRP state. The routers exchange HSRP hello messages at regular intervals so that they can remain aware of each other’s existence and that of the active router.

The router with the highest priority wins the election.

80
Q

Describe the virtual MAC address used by HSRP.

A

For the virtual router addres, HSRP defines a special MAC address of the form 0000.0c07.acxx where xx represents the HSRP group number as a two-digit hex value.

81
Q

Describe Virtual Router Redundancy Protocol (VRRP) master and backup routers and the virtual MAC address

A

VRRP provides one redundant gateway address from a group of routers. The active router is called the master router, whereas all others are in the backup state. The master router is the one with the highest router priority in the VRRP group.

The virtual router MAC address is of the form 0000.5e00.01xx, where xx is a two-digit hex VRRP group number.

82
Q

Describe the Gateway Load Balancing Protocol (GLBP) active virtual gateway and active virtual forwarder rolls.

A

One router in the GLBP group is elected the active virtual gateway (AVG). This router has the highest priority value, or the highest IP address in the group, if there is no highest priority. The AVG answers all ARP requests for the virtual router address. Which MAC address it returns depends on which load-balancing algorithm it is configured to use. The AVG assigns the necessary virtual MAC addresses to each of the routers participating in the GLBP group. You may have up to 4.

Each of these routers is referred to as an active virtual forwarder, forwarding traffic received on its virtual MAC address.

83
Q

Describe the methods Gateway Load Balancing Protocol (GLBP) uses for load balancing.

A

Round Robin: Each new ARP request for the virtual router address receives the next available virtual MAC address in reply. This method is default.

Weighted: The GLBP group interface’s weighting value determines the proportion of traffic that should be sent to that AVF. If interface tracking is not configured, the maximum weighting value configured is used to set the relative proportions among AVFs.

Host dependent: Each client that generates an ARP request for the virtual router address always receives the same virtual MAC address in reply.

84
Q

Describe catalyst supervisor redundancy modes

A

Route processor redundancy: The redundant supervisor is only partially booted and initialized. When the active module fails, the standby module must reload every other module in the switch and then initialize all the supervisor functions.

Route processor redundancy plus (RPR+): The redundant supervisor is booted, allowing the supervisor and the route engine to initialize. No layer 2 or 3 functions are started. When the active module fails, the standby module finishes initializing without reloading other switch modules allowing switch ports to retain their state.

Stateful Switchover: The redundant supervisor is fully booted and initialized. Both the startup and running configuration contents are synchronized between the supervisor modules. Layer 2 and 3 functions are ready.

85
Q

Describe nonstop forwarding

A

Nonstop forwarding is an interactive method that focuses on quickly rebuilding the Routing Information Base (RIB) table after a supervisor switchover. Instead of waiting on any configured layer 3 routing protocols to converge and rebuild the FIB, a router can use NSF to get assistance from other NSF-aware neighbors.

86
Q

Describe power over ethernet

A

Provides inline power over the UTP cable.

87
Q

What is the maximum power offered for power classes:

0 (default), 1, 2, 3, and 4?

A

0: 15.4W
1: 4.0W
2: 7.0W
3: 15.4W
4: Up to 50W

88
Q

Describe a voice VLAN

A

A unique VLAN known as the voice VLAN ID or VVID. In addition to voice, it will also carry the QoS information for the voice packets.

89
Q

Describe delay, jitter, and packet-loss

A

Delay: The amount of time it takes to get from one network device to another. The time it takes for a packet to make a round trip is called the latency.

Jitter: Variation in delay

Loss: The loss of data in its totality

90
Q

Describe best-effort delivery

A

A network that just forwards packets in the order they were received as fast as it can has no real QoS and is called best effort delivery.

91
Q

Describe the differentiated services model.

A

DiffServ requires no advance reservations; QoS is handled dynamically, in a distributed fashion. DiffServ applies QoS on a per hop basis to a whole group of similar flows. Diffserv also bases its QoS decisions on information contained in each packet header.

92
Q

Explain the Class of Service marking on a trunk link.

A

When a trunk adds a tag indicating the source VLAN number the encapsulation also includes a field that can mark the class of service (CoS) of each frame.

802.1Q: The user field contains three 802.1p priority bits that indicate the frame CoS. Native VLAN are not tagged.

Inter-Switch Link (ISL): Each fram is taged with a 15-bit VLAN ID and a 4-bit user field. The lower 3 bits of the user field are used as a class of service value.

93
Q

Describe the differentiated service codepoint classes

A

Class 0: Default class - offers only best effort forwarding

Class 1-4: Assured forwarding (AF) classes. Higher AF class numbers indicate the presence of higher-priority traffic.

Class 5: Expedited forwarding (EF): Least likely to be dropped.

Class 6-7: Internetwork control and network control respectively. Set aside for network control traffic.

Each class has three levels of drop precedence. The higher the value, the more likely it is to be dropped.

DON’T FORGET IT’S 6 BITS NOT 8!

94
Q

What is a Quality of Service (QoS) trust boundary?

A

The perimeter formed by switches that do not trust incoming QoS is called the trust boundary. Usually includes everything on the internal network except end user devices.

95
Q

Explain how to configure QoS trust on a switch interface.

A

1) Enable QoS on the switch: mls qos
* Default to untrusted

2) Define the QoS parameter that will be trusted:
interface type mod/num
mls qos trust {cos | ip-precedence | dscp}

3) mls qos trust device cisco-phone
4) switchport priority extend {cos value | trust}

96
Q

Describe the 802.11 collision avoidance mechanism.

A

Collision avoidance works be requiring all stations to listen before they transmit a frame. When a station has a frame that needs to be sent, one of the two following conditions occurs:

No other device is transmitting: The station can transmit its frame immediately. The intended receiving station must send an acknowledgement frame to confirm that the original frame arrived intact and collision-free

Another device is already transmitting a frame: The station must wait until the frame in progress has completed; then it must wait a random amount of time before transmitting its own frame.

97
Q

What is an SSID?

A

Any group of wireless devices is known as a service set. The devices must share a common service set identifier (SSID), which is a text frame included in every frame sent.

CCNP Switch Practice (4 decks)

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