Dcicn-640-911-Ch17

Front 1

What are the standards for the following variants of STP:

STP
RSTP
PVST+
MSTP

Back 1

STP - 802.1D
RSTP - 802.1W
PVST+ - Cisco Proprietary
MSTP - 802.1S - merged into 802.1Q-2005

Front 2

What are the potential issues with redundant L2 topologies?

Back 2

Unicast broadcast storms (circle the network).
Multiple frame copies (via multiple paths).
MAC database instability (MAC entries flip-flop between ports).

Front 3

What is the goal of STP?

Back 3

To calculate and implement a loop free L2 topology. It does this by blocking ports where necessary.

Front 4

What are the 4 steps of 802.1D STP?

Back 4

Root bridge selection.
Non-root bridges elect a Root Port.
Each segment elects a designated port.
All other ports become non-designated/blocking.

Front 5

How is the Root Bridge selected?

Back 5

The lowest Bridge ID.

Front 6

Describe the bridge ID.

Back 6

8 bytes in length.
Priority = 4 bits (default = 32768).
ExtSysID (VLAN ID) = 12 bits.
MAC address = 6 bytes.

Front 7

Describe ports costs.

Back 7

a. Port costs are based on bandwidth and are assigned to ports to determine Root Ports.
b. If port costs are equal there are a number of tie breakers, the last on being the port ID.

Front 8

What are the default port costs for the following link speeds?

10Mbps
1Gbps
10Gbps

Back 8

10Mbps - 100
1Gbps - 4
10Gbps - 2

Front 9

What are the port states in 802.1D STP?

Back 9

Blocking.
Listening (15 sec).
Learning (15 sec).
Forwarding.

Front 10

What was the justification for 802.1W RSTP?

Back 10

a. Faster topology calculations by replacing the timers with a proposal and agreement structure.
b. Simplified ports states - Forwarding, Discarding, Learning.
c. Additional port roles - Alternate and Backup Ports.
d. Improved topology change notifications (TCN). The local switch can provide updates instead of everything having to go via the Root Bridge as in 802.1D STP.

Front 11

Describe the port roles in 802.1W RSTP.

Back 11

a. Alternate Port - an alternative Root Port, changeover is very quick.
b. Backup Port - backup for a Designated Port.

Front 12

Describe 802.1S MSTP.

Back 12

Allows you to define the number of STP topologies in the network.
Includes all the features of RSTP

Front 13

Describe the Spanning-Tree port types.

Back 13

a. edge - will enable RSTP and shouldn't be connected to another siwtch.
b. network - used for an inter-switch link.
c. normal - default behaviour and shouldn't be used.

Front 14

Configure the following:

Mode - rapid-pvst
Int e3/3
Port type edge
VLAN 10
priority 4096

Back 14

Conf
Spanning-tree mode rapid-pvst
Int e2/3
Spanning-tree port type edge
Spanning-tree vlan 10 priority 4096

Front 15

Which command will help you to determine the STP mode in use on a switch?

Back 15

show spanning-tree summary.

Front 16

Describe an Etherchannel:

Back 16

a. Will allow multiple physical links between switches without STP blocking them.
b. Physical links make up 1 logical link.
c. Traffic is load balanced across the physical links.
d. Static or dynamic (LACP, PAGP) negotiation can be used.

Front 17

What are the LACP states?

Back 17

a. Active - will actively try to negotiate an Etherchannel with a neighbouring switch.
b. Passive - will passively establish an Etherchannel if prompted by a neighbouring switch in Active mode.

Front 18

Which LACP mode combination will result in a failed negotiation?

Back 18

Passive/Passive.