Overview

Many times we deal with customers who do not know how to configure aggregation on their own switch.  Cisco is the most popular switch vendor for most of Quantum’s customers and this document will help explain how to create an etherchannel (aggregation group) on a Cisco switch running iOS.

Configuring an Etherchannel

 

Most switches running iOS will use the same syntax to create the etherchannel but it will be best to first find the configuration guide for the customer’s specific model and use it.  To find a configuration guide for a specific model:

• Open up a web browser and go to google.com
• Type in the customer’s model number followed by configuration guide

 

Once you have opened the configuration guide you will see links for each section of the guide to the left.  You can either look for the section titled “Configuring etherchannels” or hit ctrl-f and search for etherchannel.

 

Here is the configuration guide for the 3750x model for an example.

 

It would be good to read through the entire section at least once for a single model to get a better understanding of how Cisco handles aggregation.  Within each guide you will find a section for “Configuring Layer 2 EtherChannels.”  This section will show the syntax explained in steps then an actual example.

 

Typically, it is enough to copy the link to this document and the syntax in an email and then send it to the customer and let them create it.  For example, if a customer was using a 3750x and wasn’t sure how to create an etherchannel you would send an email like the following:

 

I pulled information on how to create an etherchannel from this link:

http://www.cisco.com/en/US/docs/switches/lan/catalyst3750x_3560x/software/release/12.2_53_se/configuration/guide/swethchl.html

 

Without reading the entire page, we want to create an etherchannel using LACP in active mode. An example of the syntax you will want to use is:

Switch# configure terminal

Switch(config)# interface range gigabitethernet2/0/1 -2

Switch(config-if-range)# switchport mode access

Switch(config-if-range)# switchport access vlan 10

Switch(config-if-range)# channel-group 5 mode active

Switch(config-if-range)# end

 

• For interface range you will want to list the ports connected to the DXi
• You will then want to change the VLAN id and the channel group ID to the desired IDs in your environment.

 

If the customer doesn’t know how many channel-groups they have or which VLAN should be used for the DXi ports then it is likely that they don’t have VLANs or channel-groups created.  To be safe, you can use the following commands to determine how those ports are currently configured and what channel groups are already created:

 

• This command will show you details about port 1 on the 2nd switch in the stack.  The middle number is always 0.  Look for the line that says Access Mode VLAN and it will show you the VLAN to which that port is assigned.  Here is an example for port 19 on the first switch in the stack.  It is a member of VLAN 1:

 

Name: Gi1/0/19

Switchport: Enabled

Administrative Mode: static access

Operational Mode: static access (member of bundle Po1)

Administrative Trunking Encapsulation: negotiate

Operational Trunking Encapsulation: native

Negotiation of Trunking: Off

Access Mode VLAN: 1 (default)

Trunking Native Mode VLAN: 1 (default)

Administrative Native VLAN tagging: enabled

Voice VLAN: none

Administrative private-vlan host-association: none

Administrative private-vlan mapping: none

Administrative private-vlan trunk native VLAN: none

Administrative private-vlan trunk Native VLAN tagging: enabled

Administrative private-vlan trunk encapsulation: dot1q

Administrative private-vlan trunk normal VLANs: none

Administrative private-vlan trunk associations: none

Administrative private-vlan trunk mappings: none

Operational private-vlan: none

Trunking VLANs Enabled: ALL

Pruning VLANs Enabled: 2-1001

Capture Mode Disabled

Capture VLANs Allowed: ALL

 

Protected: false

Unknown unicast blocked: disabled

Unknown multicast blocked: disabled

Appliance trust: none

 

To get a list of the etherchannels you use the following command:

• show etherchannel

The output from this command using the same switch in the above example:

Number of channel-groups in use: 1

Number of aggregators:           1

 

Group  Port-channel  Protocol    Ports

------+-------------+-----------+-----------------------------------------------

1      Po1(SU)          -        Gi1/0/29(P) Gi1/0/31(P) Gi1/0/32(P)

                                 Gi1/0/33(P)

This states that ports 29,31,32 and 33 from the first switch in the stack are members of channel-group 1. 

 

So we’ve established that channel-group 1 already exists and that port 19 is a member of VLAN1.  For the sake of this article we will say that ports 20, 21 and 22 are also members of VLAN1.  With this information we would create a new etherchannel from privileged exec mode with the following syntax:

 

Switch# configure terminal

Switch(config)# interface range gigabitethernet1/0/19 -22

Switch(config-if-range)# switchport mode access

Switch(config-if-range)# switchport access vlan 1

Switch(config-if-range)# channel-group 2 mode active

Switch(config-if-range)# end

 

As you can see we assigned ports to vlan 1, where they are already assigned, and created a new LACP channel group in active mode, channel group 2.