Improving Redundant Switched Topologies with EtherChannel

Question 1

What are the main purposes of EtherChannel?

Answer 1

1. Adding bandwidth to uplinks or other links that carry large amounts of traffic.
2. Adds redundancy, without sacrificing bandwidth (due to spanning tree).
3. Can be used as a means of load balancing.

Question 2

What layers can be aggregated?

Answer 2

Layer 2 and Layer 3 interfaces can be aggregated.

Layer 1 can also be aggregated, an example would be combining frequency bands in wireless communications.

Question 3

How many ports and what type of ports can you group in a single EtherChannel?

Answer 3

You can group 2, 4, 6 or 8 physical interfaces into a port channel logical interface.

All of the physical interfaces must also be the same type (FastEthernet or GigabitEthernet, etc)

Question 4

What was the original EtherChannel protocol and what is the current standard protocol used?

Answer 4

Original protocol - Cisco proprietary, Port Aggregation Protocol (PAgP)

Current protocol - Initially IEEE standardized PAgP as 802.3ad aka Link Aggregation Control Protocol (LACP).

The current standard for LACP is IEEE 8021AX.

Question 5

What parameters must match on individual links to be able to implement an EtherChannel?

Answer 5

1. Interface types - An example is that you cannot have both FastEthernet and Gigabit Ethernet ports bundled into a single EtherChannel.
2. Speed and duplex
3. Switchport mode and VLAN - Access ports must have the same VLAN. Trunk ports must have the same allowed VLANs. Native VLAN must match.
4. STP settings

Question 6

What are the two modes that LACP defines?

Answer 6

LACP active - initiates negotiations with other ports by sending LACP packets

LACP passive - port responds to LACP packets, but does not initiate negotiations.

NOTE -When you configure either mode above, you automatically enable the LACP protocol on that interface.

Question 7

Where are Layer 3 interfaces bundled into EtherChannels?

Answer 7

Routed ports between switches or routers.

Mostly between Layer 3 switches or between a Layer 3 switch and a router. Also between links connecting to the WAN service provider.

Question 8

What is the primary reason to utilize LACP vs. configuring a manual EtherChannel?

Answer 8

Configuring the EtherChannel with LACP can prevent misconfiguration issues by ensuring both ends of the aggregated link fulfill the link requirements.

Question 9

What are the steps / commands for configuring a Layer 2 EtherChannel?

Answer 9

1. Use interface range command to configure interface attributes on all interfaces that are going to be aggregated [optional].
2. Shut down interfaces that will be aggregated, using the shutdown command.
3. Bundle interfaces using the channel-group command by specifying the port channel identifier and aggregation method: on / active / passive
4. Configure the port channel interface.
5. Enable interfaces that were previously shut down.

Question 10

What are the steps / commands for configuring a Layer 3 EtherChannel?

Answer 10

1. Create a logical port channel interface using interface port-channel command.
2. Turn the logical port channel interface into routed interface, using the no switchport command.
3. Assign IPv4 address to the port channel interface.
4. Use the interface range command to configure member interfaces:

• Convert member interfaces into routed ports using the no switchport command
• Bundle the interfaces using the channel-group command by specifying the logical interface identifier and aggregation method: on / active / passive

Question 11

What are some useful commands to verify EtherChannel configurations?

Answer 11

show interface port-channel - general status of the logical port channel interface

show etherchannel summary - one line of info per port channel, useful when there are several port channel interfaces on the same device

show etherchannel port-channel - info about the specific port channel interface

show ip interface port-channel - info about the IPv4 address that is configured for a L3 EtherChannel

Question 12

Does the port-channel # need to match on both sides of an EtherChannel link?

Answer 12

The port-channel number does not need to match, however it is good practice to leave them matching for easier manageability.

Question 13

What is the equivalent of LACP’s Active/Passive for PAgP?

Answer 13

Desirable / Auto

NOTE: This works the same as DTP (dynamic trunking protocol). Both Desireable = EtherChannel forms, Both Auto = no EtherChannel forms, etc…

Question 14

What is the non-Cisco term for EtherChannel?

Answer 14

LAG - Link Aggregation port

Question 15

What is the command to configure load balancing for LAGs?

Answer 15

In global config:

port-channel load-balance {src-dst-mac / dst-ip / dst-mac / src-dst-ip / src-ip / src-mac}