Ch 5: VLAN Trunks and EtherChannel Bundles Flashcards
Which of the following is not a switch role for VTP?
a. Client
b. Server
c. Proxy
d. Transparent
e. Off
C. A switch can operate with the VTP roles client, server, transparent, and off.
True or false: The VTP summary advertisement includes the VLANs that were recently added, deleted, or modified.
a. True
b. False
B. False. The VTP summary includes the VTP version, domain, configuration revision, and time stamp.
True or false: There can be only one switch in a VTP domain that has the server role.
a. True
b. False
B. False. There can be multiple VTP servers in a VTP domain. They process updates from other VTP servers just as with a client.
Which of the following is a common disastrous VTP problem with moving a switch from one location to another?
a. The domain certificate must be deleted and re-installed on the VTP server.
b. The moved switch sends an update to the VTP server and deletes VLANs.
c. The moved switch interrupts the VTP.
d. The moved switch causes an STP forwarding loop.
B. If the switch has a higher revision number than the current VTP domain, when a VLAN is deleted, it can send an update to the VTP server and remove that VLAN from all switches in the VTP domain.
True or false: If two switches are connected and configured with the command switchport mode dynamic auto, the switches will establish a trunk link.
a. True
b. False
B. False. Dynamic auto requires the other side to initiate a request in order for a trunk link to form.
The command ________ prevents DTP from communicating and agreeing upon a link being a trunk port.
a. switchport dtp disable
b. switchport disable dtp
c. switchport nonegotiate
d. no switchport mode trunk handshake
C. The command switchport nonegotiate disables DTP on a port.
True or false: PAgP is an industry standard dynamic link aggregation protocol.
a. True
b. False
B. False. PAgP is a Cisco proprietary link bundling protocol.
An EtherChannel bundle allows for link aggregation for which types of ports? (Choose all that apply.)
a. Access
b. Trunk
c. Routed
d. Loopback
A, B, and C. An EtherChannel bundle allows for a virtual port channel that acts as a Layer 2 (access or trunk) or Layer 3 routed interface.
What are the benefits of using an EtherChannel? (Choose two.)
a. Increased bandwidth between devices
b. Reduction of topology changes/convergence
c. Smaller configuration
d. Per-packet load balancing
A and B. An EtherChannel bundle provides increased bandwidth between devices and does not generate a topology change with the addition/removal of member links.
One switch has EtherChannel configured as auto. What options on the other switch can be configured to establish an EtherChannel bundle?
a. Auto
b. Active
c. Desirable
d. Passive
C. Desirable. If one device is configured with PAgP auto, the other device must be configured with desirable to form an EtherChannel bundle.
True or false: LACP and PAgP allow you to set the maximum number of member links in an EtherChannel bundle.
a. True
b. False
B. False. Only LACP allows you to set the maximum number of member links in an EtherChannel bundle.
How many roles are there in the VTP architecture? List them and their functions.
There are four roles in the VTP architecture:
- Server: The server switch is responsible for the creation, modification, and deletion of VLANs within the VTP domain.
- Client: The client switch receives VTP advertisements and modifies the VLANs on that switch. VLANs cannot be configured locally on a VTP client.
- Transparent: VTP transparent switches receive and forward VTP advertisements but do not modify the local VLAN database. VLANs are configured only locally.
- Off: A switch does not participate in VTP advertisements and does not forward them out of any ports either. VLANs are configured only locally.
How many versions of VTP are there? What is the default?
There are three versions of VTP, and Version 1 is the default. At its simplest, VTP Versions 1 and 2 limited propagation to VLANs numbered 1 to 1005. VTP Version 3 allows for the full range of VLANs 1 to 4094. At the time of this writing, most switches should be capable of running VTP Version 3.
T/F: VTP servers process updates from other VTP servers just as a client does.
True.
VTP supports having multiple VTP servers in a domain. These servers process updates from other VTP servers just as a client does. If a VTP domain is Version 3, the primary VTP server must be set with the executive command vtp primary.
T/F: VTP advertises updates by using unicast addresses across the trunk links to all the switches in the VTP domain.
False. VTP advertises updates by using a multicast address across the trunk links for advertising updates to all the switches in the VTP domain.
How many types of VTP advertisements are there? What are they?
There are three main types of advertisements:
- Summary: This advertisement occurs every 300 seconds or when a VLAN is added, removed, or changed. It includes the VTP version, domain, configuration revision number, and time stamp.
- Subset: This advertisement occurs after a VLAN configuration change occurs. It contains all the relevant information for the switches to make changes to the VLANs on them.
- Client requests: This advertisement is a request by a client to receive the more detailed subset advertisement. Typically, this occurs when a switch with a lower revision number joins the VTP domain and observes a summary advertisement with a higher revision than it has stored locally.
What is included in a VTP Summary update? How often is it sent? Hint: there are 4 things.
There are three main types of advertisements:
Summary: This advertisement occurs every 300 seconds or when a VLAN is added, removed, or changed. It includes the VTP version, domain, configuration revision number, and time stamp.
Put these steps for configuring VTP in order:
- (Optional) Secure the VTP domain with the command vtp password password. (This step is optional but recommended because it helps prevent unauthorized switches from joining the VTP domain.)
- Define the VTP domain with the command vtp domain domain-name. Note: Changing the VTP domain resets the local switch’s revision number to 0.
- Define the VTP version with the command vtp version {1 | 2 | 3}.
- Define the VTP switch role with the command vtp mode { server | client | transparent | none }.
The following are the steps for configuring VTP:
Step 1. Define the VTP version with the command vtp version {1 | 2 | 3}.
Step 2. Define the VTP domain with the command vtp domain domain-name. Changing the VTP domain resets the local switch’s revision to 0.
Step 3. Define the VTP switch role with the command vtp mode { server | client | transparent | none }.
Step 4. (Optional) Secure the VTP domain with the command vtp password password. (This step is optional but recommended because it helps prevent unauthorized switches from joining the VTP domain.)
What is the command to verify VTP?
The VTP status is verified with the command show vtp status.
The most important information displayed is the VTP version, VTP domain name, VTP mode, the number of VLANs (standard and extended), and the configuration version.
Example 5-2 shows the output for SW1, SW2, SW3, and SW4. Notice the highlighted operating mode for SW2, SW3, and SW4. The last two VTP Operating Mode entries are not relevant as they are used for other functions.
What is the danger of adding a new switch to a VTP domain?
It is very important that every switch that connects to a VTP domain has the VTP revision number reset to 0. Failing to reset the revision number on a switch could result in the switch providing an update to the VTP server. This is not an issue if VLANs are added but is catastrophic if VLANs are removed because those VLANs will be removed throughout the domain.
What happens to access ports when a VLAN is removed from a switch?
When a VLAN is removed from a switch, the access port is moved to VLAN 1. It is then necessary to reassign VLANs to every port associated to the VLAN(s) that were removed.
This can be a result of carelessly introducing a switch to a VTP domain without resetting the VTP rev number.
What is DTP and what does it do?
Dynamic Trunking Protocol packets to negotiate whether the other end can be a trunk port. If both ports can successfully negotiate an agreement, the port will become a trunk switch port. DTP advertises itself every 30 seconds to neighbors so that they are kept aware of its status.
DTP requires that the VTP domain match between the two switches.
What combination of DTP modes will not form a trunk automatically?
A trunk link can successfully form in almost any combination of these modes unless both ends are configured as dynamic auto. Table 5-2 shows a matrix for successfully establishing a dynamic trunk link.
What is the command to statically configure a link to be a trunk?
The mode for a statically configured trunk port is on and is set with this command: switchport mode trunk
A static trunk port attempts to establish and negotiate a trunk port with a neighbor by default. However, the interface configuration command switchport nonegotiate prevents that port from forming a trunk port with a dynamic desirable or dynamic auto switch port.
Example 5-7 demonstrates the use of this command on SW1’s Gi1/0/2 interface. The setting is then verified by looking at the switch port status. Notice that Negotiation of Trunk now displays as Off.
NOTE As a best practice, configure both ends of a link as a fixed port type (using switchport mode access or switchport mode trunk) to remove any uncertainty about the port’s operations.
What is the command to verify that a Port Channel has been established?
As shown in Example 5-9, the command show etherchannel summary provides an overview of all the configured EtherChannels, along with the status and dynamic aggregation protocol for each one. A second EtherChannel using PAgP was configured on the topology to differentiate between LACP and PAgP interfaces.
What is the command used to verify the logical interface?
The logical interface can be viewed with the command show interface port-channel port-channel-id. The output includes traditional interface statistics and lists the member interfaces and indicates that the bandwidth reflects the combined throughput of all active member interfaces. As the bandwidth changes, systems that reference the bandwidth (such as QoS policies and interface costs for routing protocols) adjust accordingly.
Example 5-10 shows the use of the show interface port-channel port-channel-id command on SW1. Notice that the bandwidth is 2 Gbps and correlates to the two 1 Gbps interfaces in the show etherchannel summary command.
What command is used to show the LACP system identifier? What is the function of this identifier?
The LACP system identifier is used to verify that the member interfaces are connected to the same device and not split between devices. The local LACP system ID can be viewed by using the command show lacp system-id.
show lacp neighbor [detail] will also show the system id.
What command displays additional information about the PAgP neighbor and includes the neighbor’s system ID, remote port number, and whether it is using fast or slow PAgP packet intervals as part of the output.
The command show pagp neighbor displays additional information about the PAgP neighbor and includes the neighbor’s system ID, remote port number, and whether it is using fast or slow PAgP packet intervals as part of the output.
Example 5-13 shows the use of this command.
T/F: A vital step in troubleshooting the establishment of port channels is to verify that LACP or PAgP packets are being transmitted between devices. The first troubleshooting step that can be taken is to verify the EtherChannel counters for the appropriate protocol.
True.
LACP counters are viewed with the command show lacp counters.
- The output includes a list of the EtherChannel interfaces, their associated member interfaces, counters for LACP packets sent/received, and any errors. An interface should see the sent and received columns increment over a time interval. The failure of the counters to increment indicates a problem. The problem could be related to a physical link, or it might have to do with an incomplete or incompatible configuration with the remote device. Check the LACP counters on the remote device to see if it is transmitting LACP packets.
PAgP counters are viewed with the command show pagp counters.
- The output of the PAgP command show pagp counters includes a list of the EtherChannel interfaces, their associated member interfaces, counters for PAgP packets sent/received, and any errors. The PAgP counters can be cleared with the command clear lacp counters.
What is LACP fast?
The original LACP standards sent out LACP packets every 30 seconds. A link is deemed unusable if an LACP packet is not received after three intervals, which results in a potential 90 seconds of packet loss for a link before that member interface is removed from a port channel.
An amendment to the standards was made so that LACP packets are advertised every 1 second. This is known as LACP fast because a link can be identified and removed in 3 seconds compared to the 90 seconds specified in the initial LACP standard. LACP fast is enabled on the member interfaces with the interface configuration command lacp rate fast.
NOTE All the interfaces on both switches need to be configured the same—either using LACP fast or LACP slow—for the EtherChannel to successfully come up.
Example 5-16 shows how the current LACP state can be identified on the local and neighbor interfaces, along with how an interface can be converted to LACP fast.
What is the LACP command to require a minimum number of adjacencies before a port-channel interface becomes active?
This option can be configured with the port-channel interface command port-channel min-links min-links.
Example 5-17 shows how to set the minimum number of port-channel interfaces to two and then shut down one of the member interfaces on SW1. This prevents the EtherChannel from meeting the required minimum links and shuts it down. Notice that the port-channel status is not in use in the new state.
What is the LACP command to requre an etherchannel have a specific maximum number of member interfaces in a port channel?
This may be done to ensure that the active member interface count proceeds with powers of two (for example, 2, 4, 8) to accommodate load-balancing hashes. The maximum number of member interfaces in a port channel can be configured with the port-channel interface command lacp max-bundle max-links.
The maximum number of port-channel member interfaces needs to be configured only on the master switch for that port channel; however, configuring it on both switches is recommended to accelerate troubleshooting and assist operational staff.
The port-channel master switch controls which member interfaces (and associated links) are active by examining the LACP port priority. A lower port priority is preferred. If the port priority is the same, then the lower interface number is preferred.
Example 5-18 shows the configuration of the maximum number of active member interfaces for a port channel; you can see that those interfaces now show as Hot-standby.
The _________________ identifies which switch is the master switch for a port channel.
The LACP system priority identifies which switch is the master switch for a port channel.
The master switch on a port channel is responsible for choosing which member interfaces are active in a port channel when there are more member interfaces than the maximum number of member interfaces associated with a port-channel interface. The switch with the lower system priority is preferred.
The LACP system priority can be changed with the command lacp system-priority priority.
The interface configuration command _______________ sets the interface priority.
LACP interface priority enables the master switch to choose which member interfaces are active in a port channel when there are more member interfaces than the maximum number of member interfaces for a port channel. A port with a lower port priority is preferred. The interface configuration command lacp port-priority priority sets the interface priority.
Example 5-20 changes the port priority on SW1 for Gi1/0/2 so that it is the most preferred interface when the LACP maximum link has been set to 1. SW1 is the master switch for port channel 1, the Gi1/0/2 interface becomes active, and port Gi1/0/1 becomes Hot-standby.
T/F: If the links are unevenly distributed, changing the hash value may provide a different distribution ratio across member links.
True.
If the links are unevenly distributed, changing the hash value may provide a different distribution ratio across member links.
For example, if a port channel is established with a router, using a MAC address as part of the hash could impact the traffic flow as the router’s MAC address does not change (as the MAC address for the source or destination will always be the router’s MAC address). A better choice would be to use the source/destination IP address or base the hash on TCP/UDP session ports.
The command show etherchannel load-balance displays how a switch will load balance network traffic based on its type: non-IP, IPv4, or IPv6. Example 5-21 shows the command being executed on SW1.
The command _________________ displays how a switch will load balance network traffic on a port-channel based on its type: non-IP, IPv4, or IPv6. Example 5-21 shows the command being executed on SW1.
The command show etherchannel load-balance displays how a switch will load balance network traffic based on its type: non-IP, IPv4, or IPv6. Example 5-21 shows the command being executed on SW1.
