Chapter 2) Implementing Data Center Switching Protocols

Question 1

Describe the function of Spanning Tree edge ports.

Answer 1

Edge ports in spanning tree connect directly to end hosts. These ports can be either an access port or trunk port, and immediately transition to the forwarding state.

Question 2

Describe the function of Spanning Tree network ports.

Answer 2

Network ports are normally connected only to switches or bridges. Bridge assurance is enabled only on network ports.

Question 3

Describe the function of Spanning tree normal ports.

Answer 3

Normal ports can be connected to either hosts, switches, or bridges. These ports function as normal spanning tree ports.

Question 4

What is the default spanning tree port type?

Answer 4

The default spanning tree interface is a normal port.

Question 5

What is the function of the STP Bridge Assurance extension?

Answer 5

Spanning tree Bridge Assurance is one of those features that help prevent bridging loops in Layer 2 networks. When a BPDU is not received on an interface for a certain period of time, the port is disabled until it receives BDPUs again.

Question 6

What is the function of the STP BPDU Guard extension?

Answer 6

This extension disables ports that receive a BPDU frame; it is useful for edge ports that should never be connected to another switch.

Question 7

What is the function of the STP BPDU Filtering extension?

Answer 7

This extension prevents the switch from sending or even receiving BPDUs on a specified edge port.

Question 8

What is the function of the STP Loop Guard extension?

Answer 8

This extension protects against network interfaces that malfunction. Loop Guard is useful only in switched networks where devices are connected by point-to-point links.

Question 9

What is the function of the STP Root Guard extension?

Answer 9

This extension prevents a port from becoming a root port or a blocked port.

Question 10

What is the default mode of STP for Cisco Nexus Switches?

Answer 10

Rapid PVST+

Question 11

When do designated and root ports generate a TC (Topology Change)?

Answer 11

When the interface fails to receive 3 consecutive BPDUs, or when the max age timer expires.

Question 12

What is the role and value of the TC While timer?

Answer 12

The TC While timer is equivalent to the hello interval + 1 second. While the TC While timer is running, the interface continues to set the TC flag on all BPDUs sent on that port.

Question 13

What are the 4 Rapid PVST+ and MST port states?

Answer 13

Blocking: The switch LAN port does not participate in frame forwarding.
Learning: The switch LAN port prepares to participate in frame forwarding.
Forwarding: The switch LAN port forwards frames.
Disabled: The switch LAN port does not participate in STP and does not forward frames.

Question 14

What the SPT short & high path-costs for a 10 Mbps link?

Answer 14

Short Path: 100

Long Path: 2,000,000

Question 15

What the SPT short & high path-costs for a 100 Mbps link?

Answer 15

Short Path: 19

Long Path: 200,000

Question 16

What the SPT short & high path-costs for a 1 Gbps link?

Answer 16

Short Path: 4

Long Path: 20,000

Question 17

What the SPT short & high path-costs for a 10 Gbps link?

Answer 17

Short Path: 2

Long Path: 2000

Question 18

What is the default Rapid PVST+ port priority value?

Answer 18

Default is 128.

Question 19

What is the range of Rapid PVST+ port priority values?

Answer 19

0 to 224, in increments of 32.

Question 20

What is the only Rapid PVST+ extension that is enabled on Cisco NX-OS by default?

Answer 20

STP Bridge Assurance.

Question 21

What are the maximum amount of interfaces that can be supported in a single port channel?

Answer 21

8 or 16, depending on the hardware and software support in Cisco NX-OS.

Question 22

What are the types of port channels that are supported by Cisco NX-OS?

Answer 22

Static, or LACP (Link Aggregation Control Protocol).

PAgP (Port Aggregation Protocol) is not a supported mode in Cisco NX-OS.

Question 23

What is the difference between A vPC (Virtual Port Channel) and a VSS link (Virtual Switch System)?

Answer 23

The key difference between a vPC and a VSS is that the VSS creates a single logical switch. This results in a single control plane for both management and configuration purposes. With vPCs, each Cisco Nexus switch (vPC) is managed and configured independently. A vPC allows the creation of Layer 2 port channels that span two switches.

Question 24

Describe the function of a vPC peer-keepalive or fault-tolerant link.

Answer 24

A routed “link” (it is more accurate to say path) used to resolve dual-active scenarios in which the peer link connectivityis lost.

Question 25

Describe the function of the vPC peer link.

Answer 25

This link is used to create the illusion of a single control plane by forwarding BPDUs or LACP packets to the primary vPC switch from the secondary vPC switch. It is also used to synchronize ARP and IGMP entries between both devices.

Question 26

What type of priority is preferred in vPC primary and secondary elections? How are these roles affected by preemption?

Answer 26

The device with the lower number configured as its priority is preferred. Preemption is not available in vPC so device cannot automatically take back its role as the primary switch.

Question 27

What happens to the roles of the primary and secondary vPC switches when the vPC peer link is disconnected?

Answer 27

As long as the vPC peer-keepalive (or fault-tolerant link) is still active, the vPC operational roles stay unchanged.

Question 28

What happens to the roles of the primary and secondary vPC switches when the vPC peer link AND vPC peer-keepalive (or fault-tolerant link) are both disconnected.

Answer 28

Connectivity is lost between the primary and secondary switches, so both devices take the role as the primary switch.

Question 29

Describe how BPDUs are forwarded between the primary and secondary switches in a vPC domain.

Answer 29

The vPC, by default, ensures that only the primary switch forwards BPDUs on vPCs. The BPDUs that may be received by the secondary vPC peer on a vPC port are forwarded to the primary vPC peer through the peer link for processing.

Question 30

What is a Type-1 misconfiguration in regards to vPC?

Answer 30

A Type-1 inconsistency is a mismatch in configuration(s) between the primary and secondary switches that will cause all member ports in the channel to be suspended.

Question 31

What is a Type-2 misconfiguration in regards to vPC?

Answer 31

A Type-1 inconsistency is a mismatch in configuration(s) between the primary and secondary switches that will warn the user, but will not suspend the port channel.

Question 32

What are the 2 types of vPC configuration inconsistencies?

Answer 32

Inconsistencies can be global or interface specific: - Global inconsistencies: Type-1 global inconsistencies affect all vPC member ports (but do not affect non-vPC ports). - Interface-specific inconsistencies: Type-1 interface-specific inconsistencies affect only the interface itself

Question 33

What type of misconfiguration is a mismatch of MTU value on a port in a vPC connection?

Answer 33

Type 1: The port channel will be suspended.

Question 34

What type of misconfiguration is a mismatch of Spanning tree global settings (Bridge Assurance, Loop Guard, and Root Guard)?

Answer 34

Type 1: The port channel will be suspended.

Question 35

What type of misconfiguration is a mismatch of Multiple Spanning Tree (MST) region definition (VLAN-to-instance mapping) settings?

Answer 35

Type 1: The port channel will be suspended.

Question 36

What type of misconfiguration is a mismatch of port channel modes, trunk modes, and spanning tree interface settings?

Answer 36

Type 1: The port channel will be suspended.

Question 37

How does vPC ensure that duplicate frames are not present in the toplogy?

Answer 37

One of the most important forwarding rules for vPC is that a frame that enters the vPC peer switch from the peer link cannot exit the switch from a vPC member port.

Question 38

How does HSRP function when configured as the gateway in a vPC domain?

Answer 38

In normal Hot Standby Router Protocol operation, the active HSRP interface answers ARP requests, but with a vPC, both HSRP interfaces (active and standby) can forward traffic.

Question 39

What protocol is used by vPC to synchronize ARP information between the primary and secondary switches after they are reconnected??

Answer 39

When two switches are reconnected after a failure, they use the Cisco Fabric Services protocol over Ethernet to perform bulk synchronization of the ARP table.