Query Regarding Trunking

[rai_praveen]

i know about trunk it carry multiple vlan information over trunk link but my question is that suppose i have 2 switch have one default vlan number 1 and second is 10.suppose one pc from vlan 10 ping other pc in same vlan of second switch.so trunk link only carry information about vlan 10 or it also move information about vlan 1 on  trunk at that case but because request is for vlan 10 second switch ignore vlan 1 information.

[Federico Coto Fajardo]

Hi,

By default the trunk will carry ALL VLANs.. but there's one catch... ALL VLANs mean ALL VLANs configured on the switch (that the switch knows about).

If the VLAN does not exist on the switch, will not be carry through the trunk.

You can also restrict which VLANs can be pass thorugh the trunk.

Federico.

[rai_praveen]

thanks for answer  it means all vlan information move one trunk but only vlan for which request comes is carried out on other end switch

[mohamedtag · Accepted solution]

In addition to what Federico mentioned ,

Scenario 1 :
Vlan Database of Switch contains vlan 1 & vlan 10 and you configured the Trunk Port as follows :

=========================
Interface g 0/1
switchport mode trunk
swithport encapsulation dot1q

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

And you need to allow vlan 20 over the Trunk Port , Just add VLAN 20 to the Switch vlan Database and it will be auotmatically allowed over the Trunk Port ( Since the Trunk Port is allowing All Vlans that exixts within Vlan Database of the Switch ).

Scenario 2 :
Vlan Database of Switch contains vlan 1 & vlan 10 and you configured the Trunk Port as follows :

==========================
Interface g 0/1
switchport mode trunk
swithport encapsulation dot1q
spanning tree vlan 1 cost 1
spanning tree vlan 10 cost 1

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

And you need to allow vlan 20 over the Trunk Port , you need to add VLAN 20 to the Switch vlan Database and adjust the Trunk Port Configuration to allow vlan 20 over the trunk port as follows :

Interface g 0/1
switchport mode trunk
swithport encapsulation dot1q
spanning tree vlan 1 cost 1
spanning tree vlan 10 cost 1
spanning tree vlan 20 cost 1

Regards

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[rai_praveen]

HI Mohamad

  thanks for answer i got your point just tell me why you add "spanning tree vlan 1 cost 1" command as per my knowledge this command use for manually configuring the path cost for vlan 1 then how its connected to vlan allowed on trunk.as per my knowledge brother for allowing vlan over trunk is:

interface f 0/2

switchport trunck allowed vlan 1,10

this is the command for allowing and restricting vlan over trunk

if i am write then pls explain me your second Scenario 2 why you add spanning tree vlan 1 cost 1 command

my question is that by creating trunk between two switch both switch knows each others vlan database but when i allowed certain vlans over link then switch only knows about allowed vlan.pls tell me do am i right about what i am saying.its just like VTP pruning concept na

[cadet alain · Accepted solution]

Hi Praveen,

No need to manipulate spanning-tree cost to enable communication between same vlan on 2 different switches.

All you need is VLAN configured on both, at least 1  interface in this vlan on both and a trunk between switches allowing this VLAN and that's all.

By default all VLANs are allowed on trunk but you can manually prune with the command :

interface f0/2

switchport trunk allowed vlan {add|remove|except|none|all}

Regards.

Alain.

[mohamedtag · Accepted solution]

Dear Praveen ,

The Command " Switchport trunk allowed vlan 1 ,10 , 20 " will do the job for you.

We use the " Spanning tree vlan 1 cos 1 " because over the same Switch we are having 2 Redundant Uplinks  ( 2 Giga Interfaces ) , So the Traffic has 2 Alternatives , either to pass from G 0/1 or from G0/2. You need to identify the Preferred path to prevent Loops.

Throught the "Cost" you can Specify the preferred Path ( Cost 1 is Preferred Path ). But Since you are Having only 1 Uplink , then " Swithport tunk allowed vlan 1.10 " will do the Job.

Regards

[rai_praveen]

thanks brother for your answer now all things are clear to me and today i got to learn new think about how use  redundant links through spanningtree vlan 1 cost 1 command thanks for expalining this but we can use etherchannel concept in it also to prevent loop. am i right brother

[mohamedtag · Accepted solution]

Dear Paveen ,

Well the EtherChannel is mailnly used for 3 functionalities :

1 - Link Aggregation - Increase Bandwidth by combining Links together

2 - Load Balancing - load balance of packets over an EtherChannel group

3 - Fault Tolerence - Should a link fail, the EtherChannel technology will automatically redistribute traffic across the remaining links.

Please review the Below Link about using the EtherChannel Concept with Cisco Switches:

http://www.cisco.com/en/US/tech/tk389/tk213/technologies_tech_note09186a0080094714.shtml

Regards

[rai_praveen]

mohamad brother

    very very thanks for clearing all my doubts and giving me a such wondewrful link about ether channel for more

  Again thanks