6.3.4 Packet Tracer - Troubleshoot EtherChannel Answers
Topology
Objectives
- Part 1: Examine the Physical Layer and Correct Switch Port Mode Issues
- Part 2: Identify and Correct Port Channel Assignment Issues
- Part 3: Identify and Correct Port Channel Protocol Issues
Background
A junior technician recently configured four switches. Users are complaining that the network is running slowly, and they would like you to investigate.
Port Channel Table
| Channel Group | Ports | Protocol |
|---|---|---|
| 1 | S1: G0/1, G0/2 S3: G0/1, G0/2 |
LACP active |
| 2 | S2: G0/1, G0/2 S4: G0/1, G0/2 |
LACP active |
| 3 | S1: F0/23, F0/24 S2: F0/23, F0/24 |
LACP active |
| 4 | S3: F0/23, F0/24 S4: F0/23, F0/24 |
LACP active |
| 5 | S1: F0/21, F0/22 S4: F0/21, F0/22 |
LACP active |
| 6 | S2: F0/21, F0/22 S3: F0/21, F0/22 |
LACP active |
Device Table
| Device | Group | Ports |
|---|---|---|
| S1 | 1 | G0/1, G0/2 |
| 3 | F0/23, F0/24 | |
| 5 | F0/21, F0/22 | |
| S2 | 2 | G0/1, G0/2 |
| 3 | F0/23, F0/24 | |
| 6 | F0/21, F0/22 | |
| S3 | 1 | G0/1, G0/2 |
| 4 | F0/23, F0/24 | |
| 6 | F0/21, F0/22 | |
| S4 | 2 | G0/1, G0/2 |
| 4 | F0/23, F0/24 | |
| 5 | F0/21, F0/22 |
Instructions
Part 1: Examine the Physical Layer and Correct Switch Port Mode Issues
Step 1: Look for access ports.
Examine the switches. When two or more redundant links connect the same switches, Spanning Tree protocol will only put one port in forwarding mode to prevent switching loops. You can see this in Packet Tracer. When physical ports are assigned to an EtherChannel port, they behave as one logical port. Each pair will either be operational or down.
Step 2: Verify ports are in trunk mode.
On S2, the port channel interfaces and physical interfaces that have been configured in the port channels are all configured as access ports. The physical interfaces should be configured as trunks. The port channel interfaces should also be configured as trunks.
S2# show running-config <output omitted> ! interface FastEthernet0/21 switchport mode access channel-group 6 mode active ! interface FastEthernet0/22 switchport mode access channel-group 6 mode active ! interface FastEthernet0/23 switchport mode access channel-group 3 mode active ! interface FastEthernet0/24 switchport mode access channel-group 3 mode active ! interface GigabitEthernet0/1 switchport mode access channel-group 2 mode active ! interface GigabitEthernet0/2 switchport mode access channel-group 2 mode active ! ! end
a. Verify that all physical ports in the topology are configured as trunks. Correct any ports that are in access mode.
S2(config)# interface range fastethernet 0/21 - 24, gigabitethernet 0/1 - 2 S2(config-if-range)# switchport mode trunk
b. Correct any EtherChannel ports that are not configured as trunks.
Instructor Note: Packet Tracer versions 7.2.1 and earlier do not grade the switchport mode trunk command on port-channel interfaces.
S1:
S1(config)# interface port-channel 1 S1(config-if)# switchport mode trunk
S2:
S2(config)# interface port-channel 2 S2(config-if)# switchport mode trunk S2(config-if)# interface port-channel 3 S2(config-if)# switchport mode trunk S2(config-if)# interface port-channel 6 S2(config-if)# switchport mode trunk
Part 2: Identify and Correct Port Channel Assignment Issues
Port channel interface assignment can be confusing. It is possible that errors can occur when assigning physical ports to port channels. In this case, ports F0/21 and F0/22 on S4 have been assigned to port channel group 4. They should be reassigned to port channel group 5.
Step 1: Examine port channel assignments.
The Packet Tracer topology and the Port Channel and Device tables provide details about the physical ports and their EtherChannel assignments. Use the show etherchannel summary command to learn how the EtherChannel links are configured. Verify that the switches are configured as shown in the documentation.
Step 2: Correct port channel assignments.
Correct any switch ports that are not assigned to the correct EtherChannel port.
S4(config)# interface range fastethernet 0/21 - 22 S4(config-if-range)# no channel-group S4(config-if-range)# channel-group 5 mode active
Part 3: Identify and Correct Port Channel Protocol Issues
The Network Design Team has made it a requirement that all EtherChannel links actively negotiate LACP. The physical ports on switch S3 have been configured to unconditionally establish PAgP, not LACP, EtherChannels. This must be corrected on S3 in order that the EtherChannels can be established. Note: after the change, Packet Tracer may still show "PAgP" in the Protocol column of the show etherchannel summary output; the port channels are working correctly when they show SU and every member port shows (P), and show running-config confirms that the ports use channel-group mode active (LACP).
Step 1: Identify protocol issues.
In 2000, the IEEE released 802.3ad (LACP), which is an open standard version of EtherChannel. For compatibility reasons, the network design team chose to use LACP across the network. The design team has made it a requirement that all ports that participate in EtherChannel need to actively negotiate the link as LACP. Verify that the physical ports are configured as indicated in the topology and Port Channel Table.
S3# show etherchannel summary
Flags: D - down P - in port-channel
I - stand-alone s - suspended
H - Hot-standby (LACP only)
R - Layer3 S - Layer2
U - in use f - failed to allocate aggregator
u - unsuitable for bundling
w - waiting to be aggregated
d - default port
Number of channel-groups in use: 3
Number of aggregators: 3
Group Port-channel Protocol Ports
------+-------------+-----------+----------------------------------------------
1 Po1(SD) PAgP Gig0/1(I) Gig0/2(I)
4 Po4(SD) PAgP Fa0/23(I) Fa0/24(I)
6 Po6(SD) PAgP Fa0/21(I) Fa0/22(I)Step 2: Correct Protocol issues.
a. Correct any switch ports that are not negotiating using LACP.
S3(config)# interface range gigabitethernet 0/1 - 2 S3(config-if-range)# no channel-group S3(config-if-range)# channel-group 1 mode active S3(config-if-range)# interface range fastethernet 0/21 - 22 S3(config-if-range)# no channel-group S3(config-if-range)# channel-group 6 mode active S3(config-if-range)# interface range fastethernet 0/23 - 24 S3(config-if-range)# no channel-group S3(config-if-range)# channel-group 4 mode active
b. Reissue the show etherchannel summary command to verify that all EtherChannel links are now correctly configured.
S3# show etherchannel summary
Flags: D - down P - in port-channel
I - stand-alone s - suspended
H - Hot-standby (LACP only)
R - Layer3 S - Layer2
U - in use f - failed to allocate aggregator
u - unsuitable for bundling
w - waiting to be aggregated
d - default port
Number of channel-groups in use: 3
Number of aggregators: 3
Group Port-channel Protocol Ports
------+-------------+-----------+----------------------------------------------
1 Po1(SU) PAgP Gig0/1(P) Gig0/2(P)
4 Po4(SU) PAgP Fa0/23(P) Fa0/24(P)
6 Po6(SU) PAgP Fa0/21(P) Fa0/22(P)Device Configs - Final
SWITCH S1
! ============================================================== !--- 6.3.4 Packet Tracer - Troubleshoot EtherChannel !--- FIX SCRIPT FOR SWITCH S1 !--- Usage: copy this whole file and paste it into the S1 terminal (start at the S1> prompt). Every line beginning with "!" is a comment; IOS ignores it, so pasting a comment by accident is harmless. ! ============================================================== enable configure terminal ! -------------------------------------------------------------- !--- Part 1: Examine the Physical Layer and Correct Switch Port Mode Issues. ! -------------------------------------------------------------- !--- b. Port-channel 1 (link to S3) is a trunk, like its member ports. interface port-channel 1 switchport mode trunk exit end ! -------------------------------------------------------------- !--- Save the configuration to NVRAM. (Press Enter when prompted for the destination filename.) ! -------------------------------------------------------------- copy running-config startup-config ! ============================================================== !--- Verification: !--- show interfaces trunk -> Po1 listed as trunking !--- show etherchannel summary -> 1 Po1(SU) LACP Gig0/1(P) Gig0/2(P) (after S3 is fixed in Part 3) ! ==============================================================
SWITCH S2
! ============================================================== !--- 6.3.4 Packet Tracer - Troubleshoot EtherChannel !--- FIX SCRIPT FOR SWITCH S2 !--- Usage: copy this whole file and paste it into the S2 terminal (start at the S2> prompt). Every line beginning with "!" is a comment; IOS ignores it, so pasting a comment by accident is harmless. ! ============================================================== enable configure terminal ! -------------------------------------------------------------- !--- Part 1: Examine the Physical Layer and Correct Switch Port Mode Issues. ! -------------------------------------------------------------- !--- a. Every physical EtherChannel member port (F0/21-24, G0/1-2) changes from access to trunk. interface range fastethernet 0/21 - 24, gigabitethernet 0/1 - 2 switchport mode trunk exit !--- b. The logical Port-channel 2, 3 and 6 interfaces are trunks too. interface port-channel 2 switchport mode trunk exit interface port-channel 3 switchport mode trunk exit interface port-channel 6 switchport mode trunk exit end ! -------------------------------------------------------------- !--- Save the configuration to NVRAM. (Press Enter when prompted for the destination filename.) ! -------------------------------------------------------------- copy running-config startup-config ! ============================================================== !--- Verification: !--- show interfaces trunk -> Po2, Po3 and Po6 listed as trunking !--- show etherchannel summary -> Po2(SU), Po3(SU), Po6(SU), every member (P) (Po6 after S3 is fixed in Part 3) ! ==============================================================
SWITCH S3
! ============================================================== !--- 6.3.4 Packet Tracer - Troubleshoot EtherChannel !--- FIX SCRIPT FOR SWITCH S3 !--- Usage: copy this whole file and paste it into the S3 terminal (start at the S3> prompt). Every line beginning with "!" is a comment; IOS ignores it, so pasting a comment by accident is harmless. ! ============================================================== enable configure terminal ! -------------------------------------------------------------- !--- Part 3: Identify and Correct Port Channel Protocol Issues. ! -------------------------------------------------------------- !--- a. Group 1 (G0/1-2, to S1): remove the PAgP channel-group, rejoin with LACP active. interface range gigabitethernet 0/1 - 2 no channel-group channel-group 1 mode active exit !--- a. Group 6 (F0/21-22, to S2): remove the PAgP channel-group, rejoin with LACP active. interface range fastethernet 0/21 - 22 no channel-group channel-group 6 mode active exit !--- a. Group 4 (F0/23-24, to S4): remove the PAgP channel-group, rejoin with LACP active. interface range fastethernet 0/23 - 24 no channel-group channel-group 4 mode active exit end ! -------------------------------------------------------------- !--- Save the configuration to NVRAM. (Press Enter when prompted for the destination filename.) ! -------------------------------------------------------------- copy running-config startup-config ! ============================================================== !--- Verification: !--- show etherchannel summary -> Po1(SU), Po4(SU), Po6(SU), every member (P) !--- Note: Packet Tracer may still print "PAgP" in the Protocol column after the change; show running-config confirms "channel-group X mode active" (LACP). ! ==============================================================
SWITCH S4
! ============================================================== !--- 6.3.4 Packet Tracer - Troubleshoot EtherChannel !--- FIX SCRIPT FOR SWITCH S4 !--- Usage: copy this whole file and paste it into the S4 terminal (start at the S4> prompt). Every line beginning with "!" is a comment; IOS ignores it, so pasting a comment by accident is harmless. ! ============================================================== enable configure terminal ! -------------------------------------------------------------- !--- Part 2: Identify and Correct Port Channel Assignment Issues. ! -------------------------------------------------------------- !--- Step 2. F0/21-22 belong to group 5 (to S1), not group 4: remove them from group 4, then join group 5 with LACP active. interface range fastethernet 0/21 - 22 no channel-group channel-group 5 mode active exit end ! -------------------------------------------------------------- !--- Save the configuration to NVRAM. (Press Enter when prompted for the destination filename.) ! -------------------------------------------------------------- copy running-config startup-config ! ============================================================== !--- Verification: !--- show etherchannel summary -> 4 Po4(SU) LACP Fa0/23(P) Fa0/24(P) (after S3 is fixed) and 5 Po5(SU) LACP Fa0/21(P) Fa0/22(P) ! ==============================================================
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6.2.4 Packet Tracer – Configure EtherChannel
