D-It Week 1 And 2 Chapter 2

Front 1

List and describe the fields found in the Original Format Bridge ID, and the System ID Extension

Back 1

The bridge ID, or BID, is a field inside a BPDU packet. It is eight bytes in length. The first two bytes are the bridge priority, an unsigned integer of 0-65,535. The last six bytes are a MAC address supplied by the bridge. Prior to IEEE 802.1D-2004, the first two bytes gave a 16 bit bridge priority.

Front 2

List the STP defaults and the commands used to change the defaults

Back 2

BID priority

Base: 32,768

spanning-tree vlan “vlan-id” root {primary | secondary}

spanning-tree vlan “vlan-id” priority “priority”

Interface cost

100 for 10 Mbps

19 for 100 Mbps

4 for 1 Gbps

2 for 10 Gbps

spanning-tree vlan "vlan-id" cost “cost”

PortFast

not enabled

spanning-tree portfast

BPDU Guard

not enabled

Spanning-tree bpduguard enabled

Front 3

Describe the logic in how the spanning-tree root primary command picks a new base STP priority

Back 3

If the current root has a base priority higher than 24,576, the local switch uses a base priority of 24,576

If the current root’s base priority is 24,576 or lower, the local switch sets its base priority to the highest multiple of 4096 that still results in the local switch becoming root.

Front 4

List the steps to configure an EtherChannel manually

Back 4

add the channel-group number mode on interface subcommand under each physical interface that should be in the channel.

Use the same number for all commands on the same switch, but the channel group number on the neighboring switch can differ.

Front 5

List the strategy for finding the root switch

Back 5

Begin with a list or diagram of switches, and consider all as possible root switches.

Rule out any switches that have an RP (show spanning-tree, show spanning-tree root), because root switches do to have a RP.

Always try show spanning-tree, because root switches do h=not have a RP.

Always try show spanning-tree, because it identifies the local switch as root indirectly: the RP column is empty if the local switch is the root.

When using a sim, rather than try switches randomly, chase the RPs.

When using a Sim, using show spanning-tree vlan x o a few switches, and recording the root switch, RP and DP ports can quickly show you most STP facts.

Front 6

List the strategy for finding the root port on nonroot switches

Back 6

Use the show spanning tree and show spanning-tree root commands. These both list the root port, and the first of these also lists the root cost

Show spanning-tree command list cost in two places: the root cost at the top, in the section about the root switch; and the interface cost at the bottom in the per interface section.

for problems where you have to calculate a switch’s root cost:

memorize the default cost values: 100 for 10 Mbps, 19 for 100 Mbps, 4 for 1 Gbps, and 2 for 10 Gbps

look for any evidence of the spanning-tree cost configuration command on an interface, because it overrides the default cost. Do not assume default costs are used.

When you know a default cost is used, if you can check the current actual speed as well. Cisco switches choose STP cost defaults based on the current speed, not the maximum speed.

Front 7

List the strategy for finding the designated port

Back 7

For switches connected to the same LAN segment, The switch with the lowest cost to reach the root, as advertised in the hello they send onto the link, becomes the DP on that link.

In case of a tie, among the switches that tied on cost, the switch with the lowest BID becomes the DP.

Front 8

List and define the actions of STP convergence

Back 8

for interfaces that stay in the same STP state, nothing needs to change.

For interfaces that need to move from a forwarding state to a blocking state, the switch immediately changes the state to blocking.

For interfaces that need to move from a blocking state to a forwarding state, the switch first moves the interface to listening state, then learning state, each for the time specified by the forward delay timer (default 15 seconds). Only then is the interfaces placed into forwarding state.

Front 9

List the interface settings that must match with other interfaces to be included in an EtherChannel on a single switch

Back 9

on the local switch, all the channel-group commands for all the physical interfaces must use the same channel-group number.

the channel-group number can be different on the neighboring switches

if you use the desirable keyword on one switch, the switch uses PAgP; the other switch must use either desirable or auto.

if you use the active keyword on one switch, the switch uses LACP; the other switch must use either active or passive.

Front 10

Define the following terms: Rapid PVST+, PVST+, PAgP, LACP, PortChannel

Back 10

Rapid PVST+ - is a cisco proprietary improvement on the IEEE standard per-VLAN a STP mode.

PVST+ - Cisco proprietary mode in STP which is an improvement on the IEEE standard

PAgP - Port Aggregation Protocol (PAgP) is a Cisco Systems proprietary networking protocol, which is used for the automated, logical aggregation of Ethernet switch ports, known as an etherchannel. This means it can only be used between Cisco switches and/or switches from licensed vendors.

LACP - A similar purpose protocol to PAgP known as LACP, released by the IEEE known as 802.3ad, is an industry standard and is not tied to any specific vendor.

PortChannel - A port channel bundles up to eight individual interfaces into a group to provide increased bandwidth and redundancy. Port channeling also load balances traffic across these physical interfaces. The port channel stays operational as long as at least one physical interface within the port channel is operational.

Front 11

Define the following commands:

spanning-tree mode {pvst | rapid-pvst | mst }

spanning-tree vlan vlan-number root primary

spanning-tree vlan vlan-number root secondary

spanning-tree [vlan vlan-number] cost cost

channel-group channel-group-number mode {auto | desirable | active | passive | on}

spanning-tree portfast

Back 11

spanning-tree mode {pvst | rapid-pvst | mst }

global configuration command to set the STP mode.

spanning-tree vlan vlan-number root primary

global configuration command that changes this switch to the root switch. The switch’s priority is changed to the lower of either 24,576 or 4096 less than the priority of the current root bridge when the command was issued.

spanning-tree vlan vlan-number root secondary

global configuration command that sets this switch’s STP base priority to 28,672.

spanning-tree [vlan vlan-number] cost cost

interface subcommand that changes the STP cost to the configured value.

channel-group channel-group-number mode {auto | desirable | active | passive | on}

Interface subcommand that enables EtherChannel on the interface.

spanning-tree portfast

Interfaces subcommand that enable portfast on the interface.