Troubleshooting
Interface Confirmation Commands
Commands that provide information about the state of the switch ports include:
Some diagnostic show commands
S1# show interfaces | include Ethernet S1# show interface status S1# show interfaces trunk
show interfaces port-channel
The show interfaces port-channel command displays the general status of the port channel interface. In the figure, the Port Channel 1 interface is up.
The “show interfaces port-channel” command
S1# show interfaces port-channel 1
Port-channel1 is up, line protocol is up (connected)
Hardware is EtherChannel, address is c07b.bcc4.a981 (bia c07b.bcc4.a981)
MTU 1500 bytes, BW 200000 Kbit/sec, DLY 100 usec,
reliability 255/255, txload 1/255, rxload 1/255
(output omitted)
show etherchannel summary
When several port channel interfaces are configured on the same device, use the show etherchannel summary command to display one line of information per port channel. In the output, the switch has one EtherChannel configured; group 1 uses LACP.
The interface bundle consists of the FastEthernet0/1 and FastEthernet0/2 interfaces. The group is a Layer 2 EtherChannel and it is in use, as indicated by the letters SU next to the port channel number.
The “show etherchannel summary” command
S1# 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
m - not in use, port not aggregated due to minimum links not met
u - unsuitable for bundling
w - waiting to be aggregated
d - default port
A - formed by Auto LAG
Number of channel-groups in use: 1
Number of aggregators: 1
Group Port-channel Protocol Ports
------+-------------+-----------+-----------------------------------------------
1 Po1(SU) LACP Fa0/1(P) Fa0/2(P)
show etherchannel port-channel
Use the show etherchannel port-channel command to display information about a specific port channel interface, as shown in the output. In the example, the Port Channel 1 interface consists of two physical interfaces, FastEthernet0/1 and FastEthernet0/2. It uses LACP in active mode. It is properly connected to another switch with a compatible configuration, which is why the port channel is said to be in use.
The “show etherchannel port-channel” command
S1# show etherchannel port-channel
Channel-group listing:
----------------------
Group: 1
----------
Port-channels in the group:
---------------------------
Port-channel: Po1 (Primary Aggregator)
------------
Age of the Port-channel = 0d:01h:02m:10s
Logical slot/port = 2/1 Number of ports = 2
HotStandBy port = null
Port state = Port-channel Ag-Inuse
Protocol = LACP
Port security = Disabled
Load share deferral = Disabled
Ports in the Port-channel:
Index Load Port EC state No of bits
------+------+------+------------------+-----------
0 00 Fa0/1 Active 0
0 00 Fa0/2 Active 0
Time since last port bundled: 0d:00h:09m:30s Fa0/2
show interfaces etherchannel
On any physical interface member of an EtherChannel bundle, the show interfaces etherchannel command can provide information about the role of the interface in the EtherChannel, as shown in the output. The interface FastEthernet0/1 is part of the EtherChannel bundle 1. The protocol for this EtherChannel is LACP.
The “show interfaces etherchannel” command
S1# show interfaces f0/1 etherchannel
Port state = Up Mstr Assoc In-Bndl
Channel group = 1 Mode = Active Gcchange = -
Port-channel = Po1 GC = - Pseudo port-channel = Po1
Port index = 0 Load = 0x00 Protocol = LACP
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 Flags State Priority Key Number State
Fa0/1 SA bndl 32768 0x1 0x1 0x102. 0x3D
Partner's information:
LACP port Admin Oper Port Port
Port Flags Priority Dev ID Age key Key Number State
Fa0/1 SA 32768 c025.5cd7.ef00 12s 0x0 0x1 0x102 0x3D
Age of the port in the current state: 0d:00h:11m:51s
Allowed vlan 1,2,20
Common issues with EtherChannel configurations
All interfaces within an EtherChannel must have the same configuration of speed and duplex mode, native and allowed VLANs on trunks, and access VLAN on access ports. Ensuring these configurations will significantly reduce network problems related to EtherChannel. Common EtherChannel issues include the following:
- Assigned ports in the EtherChannel are not part of the same VLAN, or not configured as trunks. Ports with different native VLANs cannot form an EtherChannel.
- Trunking was configured on some of the ports that make up the EtherChannel, but not all of them. It is not recommended that you configure trunking mode on individual ports that make up the EtherChannel. When configuring a trunk on an EtherChannel, verify the trunking mode on the EtherChannel.
- If the allowed range of VLANs is not the same, the ports do not form an EtherChannel even when PAgP is set to the auto or desirable mode.
- The dynamic negotiation options for PAgP and LACP are not compatibly configured on both ends of the EtherChannel.
Note: It is easy to confuse PAgP or LACP with DTP, because they are all protocols used to automate behavior on trunk links. PAgP and LACP are used for link aggregation (EtherChannel). DTP is used for automating the creation of trunk links. When an EtherChannel trunk is configured, typically EtherChannel (PAgP or LACP) is configured first and then DTP.