EthernetChannel config

Answered Question
Dec 12th, 2009

Hi,

Grateful if the expert would advise on the setting of EthernetChannel.

#

interface GE1/0/25

switchport trunk encapsulation dot1q

switchport mode {access | trunk}

If the setting was configured as "switchport mode access", what was the different behaviour comparing with the ethernet channel which was configured to be "switchport mode trunk"?

Rdgs
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Correct Answer by Giuseppe Larosa about 6 years 12 months ago

Hello Anita,

before setting up an etherchannel, configuration of all member links must match for the following criteria:

speed

duplex

switchport mode (access or trunk)

access vlan (if access port)

list of permitted vlans and native vlan (if trunk)

trunking protocol (if trunk)

after the etherchannel is up any change has to be done on the port-channel interface not on member links.

Trying to change config on one member link can cause bridging loops and has to be avoided.

If before setting the bundle, one interface's config doesn't match it should be left out of the bundle by the switch.

Note:

if the question is simply what is the effects of those two commands together:

switchport mode access:   the whole port is in a single vlan as specified by switchport access vlan, default value: switchport access vlan 1

switchport mode trunk:  the port is unconditionally a trunk regardless of the willingless of other side ( DTP messages are not considered), the port is member of multiple vlans, default value the port is member of all existing vlans in vlan database.

list of permitted vlans can be defined with:

switchport trunk allowed vlan

switchport trunk encapsulation dot1q:  specifies that is port switchport state is trunking the protocol to be used id 802.1Q for vlan tagging.

notice that until the port is in switchport mode access the switchport trunk enc dot1q is not effective and doesn't disturb.

Hope to help

Giuseppe

Correct Answer by vvasisth about 6 years 12 months ago

here is a link to provide you a better understanding of ether channel. the config remains the same till the time we are using IOS not CatOS on a switch :-

http://www.cisco.com/en/US/docs/switches/lan/catalyst3750/software/release/12.2_44_se/configuration/guide/swethchl.html

just an overview we use etherhannel to provide extra bandwidth and redundancy. once 2 or more port are configured as etherchannel they start acting as one logical port you can make it a access port, trunk port and even a layer 3 port.

when you ask the diff b/w ether channel configured as an access port or a trrunk port the answer remains the same a trunk can carry date of more than one vlan but an access port can only carry data of 1 vlan.

Regards,

Varun

Correct Answer by Jon Marshall about 6 years 12 months ago

anitachoi3 wrote:

Hi,

Grateful if the expert would advise on the setting of EthernetChannel.

#

interface GE1/0/25

switchport trunk encapsulation dot1q

switchport mode {access | trunk}

If the setting was configured as "switchport mode access", what was the different behaviour comparing with the ethernet channel which was configured to be "switchport mode trunk"?

Rdgs

Anita

Not sure what you are asking here.

Firstly the above is not an example of an etherchannel. It is a single port. For etherchannel you would need to use multiple physical ports and then you would have a port-channel interface.

The difference between an access port and a trunk port is that an access port carries one vlans traffic whereas a trunk port can carry multiple vlan traffic.

Jon

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Correct Answer
Jon Marshall Sun, 12/13/2009 - 02:15

anitachoi3 wrote:

Hi,

Grateful if the expert would advise on the setting of EthernetChannel.

#

interface GE1/0/25

switchport trunk encapsulation dot1q

switchport mode {access | trunk}

If the setting was configured as "switchport mode access", what was the different behaviour comparing with the ethernet channel which was configured to be "switchport mode trunk"?

Rdgs

Anita

Not sure what you are asking here.

Firstly the above is not an example of an etherchannel. It is a single port. For etherchannel you would need to use multiple physical ports and then you would have a port-channel interface.

The difference between an access port and a trunk port is that an access port carries one vlans traffic whereas a trunk port can carry multiple vlan traffic.

Jon

Correct Answer
vvasisth Sun, 12/13/2009 - 02:54

here is a link to provide you a better understanding of ether channel. the config remains the same till the time we are using IOS not CatOS on a switch :-

http://www.cisco.com/en/US/docs/switches/lan/catalyst3750/software/release/12.2_44_se/configuration/guide/swethchl.html

just an overview we use etherhannel to provide extra bandwidth and redundancy. once 2 or more port are configured as etherchannel they start acting as one logical port you can make it a access port, trunk port and even a layer 3 port.

when you ask the diff b/w ether channel configured as an access port or a trrunk port the answer remains the same a trunk can carry date of more than one vlan but an access port can only carry data of 1 vlan.

Regards,

Varun

Correct Answer
Giuseppe Larosa Sun, 12/13/2009 - 04:25

Hello Anita,

before setting up an etherchannel, configuration of all member links must match for the following criteria:

speed

duplex

switchport mode (access or trunk)

access vlan (if access port)

list of permitted vlans and native vlan (if trunk)

trunking protocol (if trunk)

after the etherchannel is up any change has to be done on the port-channel interface not on member links.

Trying to change config on one member link can cause bridging loops and has to be avoided.

If before setting the bundle, one interface's config doesn't match it should be left out of the bundle by the switch.

Note:

if the question is simply what is the effects of those two commands together:

switchport mode access:   the whole port is in a single vlan as specified by switchport access vlan, default value: switchport access vlan 1

switchport mode trunk:  the port is unconditionally a trunk regardless of the willingless of other side ( DTP messages are not considered), the port is member of multiple vlans, default value the port is member of all existing vlans in vlan database.

list of permitted vlans can be defined with:

switchport trunk allowed vlan

switchport trunk encapsulation dot1q:  specifies that is port switchport state is trunking the protocol to be used id 802.1Q for vlan tagging.

notice that until the port is in switchport mode access the switchport trunk enc dot1q is not effective and doesn't disturb.

Hope to help

Giuseppe

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