350-401 EtherChannel — 20 Questions

Question 1

A network engineer is configuring EtherChannel between two Cisco Catalyst switches. The ports are configured as access ports in VLAN 10. After configuring the port-channel interface and adding the physical ports, the engineer notices that the EtherChannel does not come up. The show etherchannel summary command shows the port-channel in a down state. What is the most likely cause?

Accepted Answer

The physical ports are configured as access ports in VLAN 10, but the port-channel interface is not configured with the same VLAN.. The correct answer is that the physical ports must be configured identically, including the allowed VLAN list. For access ports, the VLAN must match. The wrong answers involve issues that would not prevent the channel from forming if the VLANs match.

Answer

The physical ports have different duplex settings.

Answer

The switch is using PAgP and the neighbor is using LACP.

Answer

The physical ports are in different VLANs.

Question 2

An engineer is troubleshooting an EtherChannel between two switches. The show etherchannel summary output shows that the port-channel is up, but only one physical link is active. The other three links are in a suspended state. The physical ports are all configured identically with the same VLAN allowed. What is the most likely cause?

Accepted Answer

The port-channel has been configured with the 'port-channel max-links 1' command.. The correct answer is that the maximum number of active ports in the port-channel has been configured to 1. The wrong answers involve misconfigurations that would affect all ports or prevent the channel from forming.

Answer

The port-channel has been configured with the 'channel-group 1 mode on' command, but the physical ports are using different speeds.

Answer

The port-channel has been configured with the 'port-channel min-links 1' command.

Answer

The physical ports are in different VLANs.

Question 3

A network engineer is configuring an EtherChannel between a Cisco switch and a server that supports LACP. The switch ports are configured as trunk ports allowing multiple VLANs. The engineer wants to ensure the EtherChannel forms automatically without manual intervention. Which configuration should be applied on the switch?

Accepted Answer

Configure the port-channel with 'channel-group 1 mode active'.. The correct answer is LACP active mode, which initiates negotiation. The wrong answers either use passive mode (which waits for the other side) or static mode (which does not negotiate).

Answer

Configure the port-channel with 'channel-group 1 mode passive'.

Answer

Configure the port-channel with 'channel-group 1 mode desirable'.

Answer

Configure the port-channel with 'channel-group 1 mode on'.

Question 4

A network engineer is troubleshooting an EtherChannel between two Cisco switches. The show etherchannel 1 port-channel command shows the port-channel is up, but traffic is not load-balanced evenly. The engineer notices that all traffic is using only one link. The physical ports are all configured identically. What is the most likely cause?

Accepted Answer

The load-balancing method is set to src-dst-ip, and all traffic is between the same two IP addresses.. The correct answer is that the load-balancing method is set to src-dst-ip, but the traffic is from a single source to a single destination IP. The wrong answers involve issues that would prevent the channel from being up or affect all links.

Answer

The load-balancing method is set to src-mac, and the traffic is from multiple MAC addresses.

Answer

The physical ports have different speeds.

Answer

The port-channel is configured with 'lacp fast-switchover'.

Question 5

A network engineer is configuring EtherChannel between two Cisco switches using LACP. The engineer wants to ensure that if fewer than two links are operational, the EtherChannel does not come up. Which command should be configured?

Accepted Answer

Configure 'port-channel min-links 2' under the port-channel interface.. The correct answer is 'port-channel min-links 2', which sets the minimum number of active links required. The wrong answers either set maximum links or are unrelated.

Answer

Configure 'lacp min-bundle 2' under the port-channel interface.

Answer

Configure 'channel-group 1 mode active' on the physical ports.

Answer

Configure 'port-channel max-links 2' under the port-channel interface.

Question 6

A network engineer is configuring an EtherChannel between two Cisco switches. The engineer wants to use PAgP and ensure that the channel forms only if the neighboring switch is also configured for PAgP. Which mode should be configured on the local switch?

Accepted Answer

Configure 'channel-group 1 mode desirable' on the physical ports.. The correct answer is 'desirable' because it actively negotiates with the neighbor. The wrong answers either use LACP or force the channel without negotiation.

Answer

Configure 'channel-group 1 mode auto' on the physical ports.

Answer

Configure 'channel-group 1 mode active' on the physical ports.

Answer

Configure 'channel-group 1 mode on' on the physical ports.

Question 7

A network engineer is configuring an EtherChannel between a Cisco switch and a router. The switch ports are configured as trunk ports with allowed VLANs 10, 20, and 30. The router is configured with subinterfaces for each VLAN. After configuring the EtherChannel, the engineer notices that the router can ping devices in VLAN 10 but not in VLAN 20 or 30. What is the most likely cause?

Accepted Answer

The native VLAN is configured as VLAN 1 on the switch but VLAN 10 on the router.. The correct answer is that the native VLAN mismatch is causing issues. The wrong answers involve misconfigurations that would affect all VLANs or are unrelated.

Answer

The allowed VLAN list on the switch does not include VLAN 20 and 30.

Answer

The router subinterfaces are configured with the wrong encapsulation.

Answer

The EtherChannel is configured with 'lacp system-priority' that is too high.

Question 8

A network engineer is troubleshooting an EtherChannel between two Cisco switches. The show etherchannel summary command shows the port-channel is up, but the show interfaces trunk command shows that the trunk is not passing traffic for VLAN 100. The allowed VLAN list on the port-channel interface includes VLAN 100. What is the most likely cause?

Accepted Answer

One of the physical ports in the EtherChannel has VLAN 100 removed from its allowed list.. The correct answer is that the VLAN is not allowed on one of the physical ports. The wrong answers involve issues that would affect all VLANs or are unrelated.

Answer

The native VLAN is configured as VLAN 100 on one side.

Answer

The port-channel is configured with 'switchport trunk allowed vlan add 100' but the physical ports have 'switchport trunk allowed vlan except 100'.

Answer

The VLAN 100 does not exist on the switch.

Question 9

A network engineer is configuring an EtherChannel between two Cisco switches. The engineer wants to use LACP and ensure that the local switch is the one that determines which ports are active in the channel. Which configuration should be applied?

Accepted Answer

Configure 'lacp system-priority 100' on the local switch.. The correct answer is to set the LACP system priority lower on the local switch. The wrong answers involve other LACP parameters that do not determine which switch controls active port selection.

Answer

Configure 'lacp port-priority 100' on the physical ports of the local switch.

Answer

Configure 'channel-group 1 mode active' on the physical ports.

Answer

Configure 'lacp fast-switchover' on the port-channel interface.

Question 10

A network engineer runs the following command on Switch SW1:

SW1# show etherchannel summary
Flags:  D - down        P - bundled in port-channel
        I - stand-alone s - suspended
        H - Hot-standby (LACP only)
        R - Layer3      S - Layer2
        U - in use      N - not in use, no aggregation
        f - failed to allocate aggregator

M - not in use, minimum links not met
        u - unsuitable for bundling
        w - waiting to be aggregated
        d - default port

Number of channel-groups in use: 1
Number of aggregators:           1

Group  Port-channel  Protocol    Ports
------+-------------+-----------+--------------------------------------------
1      Po1(SU)         LACP      Gi0/0(P)    Gi0/1(P)    Gi0/2(s)    Gi0/3(D)

Based on this output, what can be concluded?

Accepted Answer

Interface Gi0/2 is suspended due to a configuration mismatch.. The output shows that port-channel 1 is in use (U) and Layer2 (S). Gi0/0 and Gi0/1 are bundled (P), Gi0/2 is suspended (s), and Gi0/3 is down (D). A suspended port in LACP indicates a misconfiguration, such as mismatched port parameters (speed, duplex, VLAN, or trunk mode). The correct answer is that Gi0/2 has a configuration mismatch.

Answer

Port-channel 1 is operating as a Layer 3 interface.

Answer

Interface Gi0/3 is in standby mode waiting to join the bundle.

Answer

All four interfaces are actively forwarding traffic in the EtherChannel.

Question 11

A network engineer runs the following command on Switch SW2:

SW2# show interfaces port-channel 1 etherchannel
Port-channel1 :

Age of the Port-channel   = 0d:00h:10m:32s
Logical slot/port   = 16/1          Number of ports = 2
HotStandby port = null
Port state          = Port-channel Ag-Inuse
Protocol            =   LACP

Ports in the Port-channel:

Index   Load     Port     EC state        No of bits
------+------+------+----------------+----------
  0     00      Gi0/0    Active              4
  1     00      Gi0/1    Active              4

Time since last port bundled:    0d:00h:05m:23s    Gi0/1

Based on this output, what can be concluded?

Accepted Answer

Both member ports are in Active state, meaning they are participating in LACP negotiation.. The output shows that the port-channel is in 'Ag-Inuse' state, meaning the aggregation is active. Both Gi0/0 and Gi0/1 are in 'Active' state, which is correct for LACP. The load field shows '00' for both, indicating that load balancing is not distributing traffic evenly; this could be because there is no traffic or the load-balancing method is not effective. The correct answer is that the EtherChannel is operational with two active member ports.

Answer

The EtherChannel is not operational because the load is zero.

Answer

The port-channel is in 'Ag-Inuse' state, which means it is not yet forwarding traffic.

Answer

Load balancing is set to source-destination IP, causing the zero load values.

Question 12

A network engineer runs the following command on Switch SW3:

SW3# show etherchannel load-balance
EtherChannel Load-Balancing Configuration:
        src-dst-ip

EtherChannel Load-Balancing Operational State:
        src-dst-ip

Based on this output, what can be concluded?

Accepted Answer

The load-balancing method is based on source and destination IP addresses.. The output shows that both the configured and operational load-balancing method is 'src-dst-ip', which means the switch uses source and destination IP addresses to determine which member port to use for each flow. This is a common and valid method. The correct answer is that the load-balancing method uses both source and destination IP addresses.

Answer

The switch uses source MAC and destination MAC for load balancing.

Answer

The operational state differs from the configured state, indicating a problem.

Answer

The switch is using round-robin to distribute traffic across ports.

Question 13

A network engineer runs the following command on Switch SW4:

SW4# show etherchannel 1 detail
Channel-group number: 1
Group state = L2

Ports in the group:
-------------------

Port: Gi0/0
--------

Port state    = Up, In-Bundle
Channel group = 1           Mode = Active/PagNego
Gcchange = -
Port-channel  = Po1         GC =  0x00010001
Pseudo port-channel = Po1

Port index = 0           Load = 0x00

Flags:  S - Device is sending Slow LACPDUs
        F - Device is sending Fast LACPDUs
        A - Device is in active mode.
        P - Device is in passive mode.

Local information:

LACP port     Admin     Oper    Port        Port
Port      Flags   State     Priority      Key       Key     Number      State
Gi0/0     SA      bndl      32768         0x1       0x1     0x101       0x3D

Partner information:

LACP port     Admin     Oper    Port        Port
Port      Flags   State     Priority      Key       Key     Number      State
Gi0/0     SA      bndl      32768         0x1       0x1     0x102       0x3D

Age of the port = 0d:00h:15m:20s

Based on this output, what can be concluded?

Accepted Answer

The port is bundled and the LACP state is synchronized.. The output shows detailed LACP information for port Gi0/0. The local and partner states are both 'bndl', meaning the port is bundled. The flags 'SA' indicate the port is in active mode and sending slow LACPDUs. The port state '0x3D' is a hexadecimal representation of the LACP state, which includes bits for activity, aggregation, synchronization, collecting, distributing, and defaulted. The correct answer is that the port is actively participating in LACP and is bundled.

Answer

The port is in passive mode and waiting for the partner to initiate.

Answer

The port is sending fast LACPDUs because the flag is 'F'.

Answer

The port is not in use because the load is 0x00.

Question 14

A network engineer runs the following command on Switch SW5:

SW5# show running-config | section interface port-channel
interface Port-channel1
 switchport mode trunk
 switchport trunk allowed vlan 1-100,200-300
!
interface Port-channel2
 switchport mode access
 switchport access vlan 10
!

SW5# show interfaces trunk

Port        Mode         Encapsulation  Status        Native vlan
Po1         on           802.1q         trunking      1

Port        Vlans allowed on trunk
Po1         1-100,200-300

Port        Vlans allowed and active in management domain
Po1         1-100,200-300

Port        Vlans in spanning tree forwarding state and not pruned
Po1         1-100,200-300

Based on this output, what can be concluded?

Accepted Answer

Port-channel1 is operational as a trunk with the configured allowed VLANs.. The output shows that Port-channel1 is configured as a trunk with allowed VLANs 1-100 and 200-300. The 'show interfaces trunk' output confirms that Po1 is trunking and the allowed VLAN list matches. Port-channel2 is not shown in the trunk output, which is expected because it is an access port. The correct answer is that Port-channel1 is operational as a trunk.

Answer

Port-channel2 is also trunking but not displayed due to a software bug.

Answer

Port-channel1 is trunking and allowed VLANs include VLANs 101-199.

Answer

The native VLAN on Po1 is VLAN 10.

Question 15

A network engineer runs the following command on Switch SW6:

SW6# show etherchannel 3 summary
Flags:  D - down        P - bundled in port-channel
        I - stand-alone s - suspended
        H - Hot-standby (LACP only)
        R - Layer3      S - Layer2
        U - in use      N - not in use, no aggregation
        f - failed to allocate aggregator

M - not in use, minimum links not met
        u - unsuitable for bundling
        w - waiting to be aggregated
        d - default port

Number of channel-groups in use: 1
Number of aggregators:           1

Group  Port-channel  Protocol    Ports
------+-------------+-----------+--------------------------------------------
3      Po3(RU)         PAgP      Gi0/0(P)    Gi0/1(P)    Gi0/2(I)

Based on this output, what can be concluded?

Accepted Answer

Interface Gi0/2 is in stand-alone mode because it is not receiving PAgP packets from the neighbor.. The output shows that Port-channel3 is a Layer 3 (R) port-channel in use (U) using PAgP. Two ports (Gi0/0 and Gi0/1) are bundled (P), while Gi0/2 is in stand-alone mode (I). Stand-alone mode in PAgP means the port is not part of the channel, typically because the neighbor is not configured for PAgP or there is a mismatch. The correct answer is that Gi0/2 is not bundled and is operating as a regular interface.

Answer

Port-channel 3 is a Layer 2 EtherChannel.

Answer

All three interfaces are bundled and forwarding traffic.

Answer

The EtherChannel is not in use because the 'U' flag is missing.

Question 16

A network engineer runs the following command on Switch SW7:

SW7# show interfaces port-channel 1
Port-channel1 is up, line protocol is up (connected)
  Hardware is EtherChannel, address is aaaa.bbbb.cccc (bia aaaa.bbbb.cccc)
  Description: Link to Core
  Internet address is 192.168.1.1/30
  MTU 1500 bytes, BW 2000000 Kbit/sec, DLY 10 usec,
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation ARPA, loopback not set
  Keepalive set (10 sec)
  Full-duplex, 1000Mb/s, link type is auto, media type is unknown
  input flow-control is off, output flow-control is unsupported
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input 00:00:00, output 00:00:00, output hang never
  Last clearing of "show interface" counters never
  Input queue: 0/2000/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  5 minute input rate 1000 bits/sec, 2 packets/sec
  5 minute output rate 500 bits/sec, 1 packets/sec
     12345 packets input, 1234567 bytes, 0 no buffer
     Received 0 broadcasts (0 IP multicasts)
     0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog, 0 multicast, 0 pause input
     0 input packets with dribble condition detected
     67890 packets output, 9876543 bytes, 0 underruns
     0 output errors, 0 collisions, 2 interface resets
     0 unknown protocol drops
     0 babbles, 0 late collision, 0 deferred
     0 lost carrier, 0 no carrier, 0 pause output
     0 output buffer failures, 0 output buffers swapped out

Based on this output, what can be concluded?

Accepted Answer

The bandwidth of 2 Gbps suggests that two 1 Gbps links are aggregated.. The output shows that Port-channel1 is up with an IP address (192.168.1.1/30), indicating it is a Layer 3 interface. The bandwidth is 2 Gbps (2000000 Kbit/sec), which suggests that two 1 Gbps links are aggregated. The interface has no errors and low utilization. The correct answer is that the port-channel is a Layer 3 interface with an aggregated bandwidth of 2 Gbps.

Answer

The port-channel is a Layer 2 interface because it has an IP address.

Answer

The interface is experiencing input errors due to CRC errors.

Answer

The port-channel is operating at half-duplex.

Question 17

A network engineer runs the following command on Switch SW8:

SW8# show etherchannel 2 detail | include "Port state|Port: Gi|Partner"
Port: Gi0/0
Port state    = Up, In-Bundle
Port: Gi0/1
Port state    = Up, In-Bundle
Port: Gi0/2
Port state    = Down, Not-In-Bundle
Partner information:
Gi0/0: Partner state = bndl
Gi0/1: Partner state = bndl
Gi0/2: Partner state = down

Based on this output, what can be concluded?

Accepted Answer

Gi0/2 is not bundled because the partner is in 'down' state, indicating a physical layer issue.. The filtered output shows that Gi0/0 and Gi0/1 are up and in-bundle, with their partners also in 'bndl' state. Gi0/2 is down and not in-bundle, with its partner also down. This indicates that the physical link on Gi0/2 is down, possibly due to a cable issue or the neighbor port being down. The correct answer is that Gi0/2 is not part of the EtherChannel because the link is down.

Answer

All three ports are bundled and forwarding traffic.

Answer

The EtherChannel is using PAgP because the partner state shows 'bndl'.

Answer

Gi0/2 is in standby mode waiting to become active.

Question 18

A network engineer runs the following command on Switch SW9:

SW9# show etherchannel 4 port-channel
Port-channels in the group:
---------------------------

Port-channel: Po4    (Primary Aggregator)

Age of the Port-channel   = 0d:00h:20m:10s
Logical slot/port   = 16/4          Number of ports = 3
HotStandby port = null
Port state          = Port-channel Ag-Inuse
Protocol            =   LACP

Ports in the Port-channel:

Index   Load     Port     EC state        No of bits
------+------+------+----------------+----------
  0     00      Gi0/0    Active              4
  1     00      Gi0/1    Active              4
  2     00      Gi0/2    Standby            4

Time since last port bundled:    0d:00h:15m:00s    Gi0/1

Based on this output, what can be concluded?

Accepted Answer

The EtherChannel has a maximum bundle size of 2, so Gi0/2 is a hot-standby port.. The output shows that Gi0/0 and Gi0/1 are in 'Active' state, while Gi0/2 is in 'Standby' state. In LACP, a standby port is a hot-standby port that becomes active if an active port fails. This is configured using the 'lacp max-bundle' command or when the number of ports exceeds the maximum allowed. The correct answer is that Gi0/2 is a hot-standby port ready to take over if an active port fails.

Answer

All three ports are actively forwarding traffic in the EtherChannel.

Answer

Gi0/2 is in standby mode because it is not receiving LACP packets from the neighbor.

Answer

The port-channel is not in use because the load is zero.

Question 19

Consider the following configuration snippet:

interface Port-channel1
 switchport mode trunk
 switchport trunk allowed vlan 10,20,30
!
interface GigabitEthernet0/1
 channel-group 1 mode active
!
interface GigabitEthernet0/2
 channel-group 1 mode passive

What is the effect of this configuration?

Accepted Answer

The EtherChannel will form using LACP, and the port-channel will operate as a trunk carrying VLANs 10, 20, and 30.. The configuration creates an EtherChannel using LACP with one side in active mode and the other in passive mode. The active side initiates negotiation, so the channel will form. The port-channel interface is configured as a trunk, so the channel will carry VLANs 10, 20, and 30.

Answer

The EtherChannel will not form because both sides must use the same LACP mode.

Answer

The EtherChannel will form using PAgP because the mode is not specified as lacp.

Answer

The EtherChannel will form but only VLAN 1 will be allowed on the trunk.

Question 20

Given the following configuration:

interface Port-channel1
 no switchport
 ip address 192.168.1.1 255.255.255.0
!
interface GigabitEthernet0/1
 no switchport
 channel-group 1 mode on
!
interface GigabitEthernet0/2
 no switchport
 channel-group 1 mode on

Which statement is true about this EtherChannel?

Accepted Answer

The EtherChannel will form and operate as a Layer 3 routed interface.. The 'mode on' command forces the interface into an EtherChannel without any negotiation protocol (no LACP or PAgP). Both sides must be configured with 'mode on' for the channel to come up. The port-channel is a routed interface (no switchport) with an IP address.

Answer

The EtherChannel will form only if the neighbor also uses LACP active mode.

Answer

The EtherChannel will not form because the interfaces are in no switchport mode.

Answer

The EtherChannel will form but will use PAgP negotiation.