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Vlan Configuration

                   I have seen one  Switch,

If i Have show Vlan Brief brief ( Port No 47 which was showing under Vlan 1)

Vlan  Name               Status  Ports

--------------------------------------------------------------

1       default              active     gi1/0/47

If i have check the particular interface

Sh run interface gig1/0/47

Current configuration

{

switch port  trunk allowed vlan 143

switchport mode trunk

}

may i know what is correct vlan associated with that port..

3 ACCEPTED SOLUTIONS

Accepted Solutions
Cisco Employee

Vlan Configuration

Dinesh,

NO the above commands are not similar. They are different.

1- One is Access port:- Which means that the port belongs to Particular vlan.

2- Trunk port:- This port means you are allowing the vlan to go out of this port as tagged.

regards

Inayath

Cisco Employee

Vlan Configuration

http://www.omnisecu.com/cisco-certified-network-associate-ccna/types-of-vlan-connection-trunk-links-and-access-links.htm

Good understanding of both.

HTH

Regards

Inayath

*Plz rate this post and mark the thread as answered if it has answered your query.

Cisco Employee

Vlan Configuration

Dinesh,

Tagged :---

======

Tagged means that the vlan information is added to the frame before it is sent over a trunk link. With 802.1Q the information is added to the frame directly. ISL encapsulates the frame with the VLAN information, and does not have a native VLAN, so all frames are tagged in this manner.All vlans, except the native VLAN when using 802.1Q, are tagged when trunking.

According to the 802.1Q standard, the way to identify different vlans in a frame is by adding Vlan ID tag in the frame.  This tag identifies what vlan the frame is meant for.  If you want multiple vlans to pass via a switch interface, those vlans need to be tagged by configuring a trunk port on a cisco switch.

Untagged:---

=======

Access ports are typically untagged, meaning only one vlan passes via the interface.  There is also the case of the native vlan.  This is a vlan that is not tagged but other vlans that pass via the interface are tagged.

http://en.wikipedia.org/wiki/IEEE_802.1Q

2-

Further more in another way of explaining:

================================

Vlan is a Virtual LAN. Switch will not break Broadcast Domain While using VLAN we can break broadcast domain.

Switch having more than one vlan. if its same Vlan data can be pass through one vlan to another. if its different Vlan we need router or L3 Switch.

Tagged VLAN means frame can be tagged which vlan that frame belongs to, that can be happen in trunk port of switch. Types of Trunk Tagging protocol 802.1Q and ISL and DTP.

Untagged VLAN. Frame cant be tagged while travelling from one switch to another switch. Eg: VLAN1 Native Vlan or Management VLAN. Frame cant mention which vlan the frame belongs

HTH

Regards

Inayath

*Plz rate all usefull posts.

8 REPLIES
Cisco Employee

Vlan Configuration

Dinesh,

Thats the correct thing which you are seeing.

The port G1/0/47 belongs to Vlan1 which is by default. (As you know by default all ports belong to vlan1.)

The port G1/0/47 is the trunk port and the vlan143 has been allowed to flow through this port.

Let me give you an example:

Example:

PC------------Port G1/0/47----------Switch.

Port configuration:

Int g1//0/47

Switchport access vlan 20 >>> I am making the port to be part of vlan 20. Once you make tihs you would see the port moving from vlan 1                                   to vlan 20.

Show vlan brief

VLAN Name                             Status    Ports

---- -------------------------------- --------- -------------------------------

1  default                                    active    G1/0/46,G1/0/48

20    VLAN0020                          active    G1/0/47 >>>>>>>> See here you are not moved from vlan 1 to vlan 20.

===========

Example 2:

============

Same as yours.

Port configuration:

Int g1//0/47

switchport mode trunk  >>>>>> Trunk port. Tunk ports are the one which carries vlan infomration from one side to another side.

Switchport trunk allowed vlan 143.  >>>> I am just allowing this to be allowed on the trunk. But the port belongs to vlan 1 which is by                                         default.

Vlan  Name               Status  Ports

--------------------------------------------------------------

1       default              active     gi1/0/47

Hope this clarified your doubt.

Regards

Inayath

*Plz rate if this is helpfull.

Vlan Configuration

ya i got it..

Same configuration done on another switch.

VLAN    NAme       Status               Port

---------------------------------------------------------------

1          default             active

143       Management   Active           Gi1/47

Sh  run int Gig1/47

current configuration

{

Switch port access vlan 143

Switchport Mode access

end

What is difference between above configuration and this...

this also allows only vlan 143

above configuration allows vlan 143 only..

But above was configured as trunk but allowed vlan is only 143

configuring switch mode access is making port as access port for allowing one vlan...

I hope i explain my doubt clearly.....

Cisco Employee

Re: Vlan Configuration

Dinesh,

Yes you are understanding is perfectly correct.

Switchport access :-- Means the port is an access port and hence belongs to only one vlan which you would configure.

Switchport trunk-- This is a trunk port usually configure between the switches to allow vlans to be floded across the same.

By default all vlans are allowed on the trunk port, If in case you manually edit it then only the vlans which is allowed on the port will flow across.

HTH

RegardsInayath

*Plz rate this post and mark the thread as answered if it has answered your query.

Vlan Configuration

ya

if Switch port trunk allowed vlan 143

and

Switchport  mode access vlan 143

is similar function ?

if so  what are advantages and disadvantages of these two configuration

Cisco Employee

Vlan Configuration

Dinesh,

NO the above commands are not similar. They are different.

1- One is Access port:- Which means that the port belongs to Particular vlan.

2- Trunk port:- This port means you are allowing the vlan to go out of this port as tagged.

regards

Inayath

Cisco Employee

Vlan Configuration

http://www.omnisecu.com/cisco-certified-network-associate-ccna/types-of-vlan-connection-trunk-links-and-access-links.htm

Good understanding of both.

HTH

Regards

Inayath

*Plz rate this post and mark the thread as answered if it has answered your query.

Vlan Configuration

ya now remembered.

Trunk.. The allowed vlan will be tagged except native vlan..

Access port-- the allowed vlan are untagged..

Now one more question is basic only.. if clear me in simple way would be better.. what is advantaged for tagged and untagged.... what actually it means....

Cisco Employee

Vlan Configuration

Dinesh,

Tagged :---

======

Tagged means that the vlan information is added to the frame before it is sent over a trunk link. With 802.1Q the information is added to the frame directly. ISL encapsulates the frame with the VLAN information, and does not have a native VLAN, so all frames are tagged in this manner.All vlans, except the native VLAN when using 802.1Q, are tagged when trunking.

According to the 802.1Q standard, the way to identify different vlans in a frame is by adding Vlan ID tag in the frame.  This tag identifies what vlan the frame is meant for.  If you want multiple vlans to pass via a switch interface, those vlans need to be tagged by configuring a trunk port on a cisco switch.

Untagged:---

=======

Access ports are typically untagged, meaning only one vlan passes via the interface.  There is also the case of the native vlan.  This is a vlan that is not tagged but other vlans that pass via the interface are tagged.

http://en.wikipedia.org/wiki/IEEE_802.1Q

2-

Further more in another way of explaining:

================================

Vlan is a Virtual LAN. Switch will not break Broadcast Domain While using VLAN we can break broadcast domain.

Switch having more than one vlan. if its same Vlan data can be pass through one vlan to another. if its different Vlan we need router or L3 Switch.

Tagged VLAN means frame can be tagged which vlan that frame belongs to, that can be happen in trunk port of switch. Types of Trunk Tagging protocol 802.1Q and ISL and DTP.

Untagged VLAN. Frame cant be tagged while travelling from one switch to another switch. Eg: VLAN1 Native Vlan or Management VLAN. Frame cant mention which vlan the frame belongs

HTH

Regards

Inayath

*Plz rate all usefull posts.

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