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Connecting Cat6509 to Cat 2950

Unanswered Question
Apr 5th, 2006
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Connecting a Cat 2950 to a Cat 6509 using a cross over cable. This comes up as trunk but I don’t want it to.

When it was first connected, it led to some spanning tree errors as the port vlan at both ends were different. On the C2950, I had vlan 1 and on the C6509, I had Vlan 211. I change the port vlan to 1 on the C6509 and then this was ok but now it is trunking.

I dont want to trunk on these port. What I want it to create a connection as a normal access port in say vlan 211.

How do I do this?

And then after doing the above, will routers connected to the switch be able to talk to each other via vlan 211?

I am running CatOS on the 6509 and IOS on the 2950.


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mahmoodmkl Wed, 04/05/2006 - 04:26
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configure the ports as access ports for the vlan which u want.create the vlan both on 6509 and 2950.

disable trunking on the ports.see that all u r routers are in vlan which u want ie 211.

Foe eg

on 6509

set vlan 211 2/2

and on 2950

switchport mode access

switchport access vlan 211



amit-singh Wed, 04/05/2006 - 04:27
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Do the following

On 2950

conf t

int fa x/y

switchport mode access

switchport access vlan

switchport nonegotiate

On Cat 6500

If trunk is there then,

set trunk x/y off

set vlan x (vlan#) y/z (port#)

for example

set trunk 2/23 off

set vlan 100 2/23



HTH, Please rate if it does.

-amit singh

londint Wed, 04/05/2006 - 06:19
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Thanks Amit

The C2950 is on a remote site. The remote site have said that they do not have any VTP configured as the C2950 is being used as just a hub, so thereby the will not be able to configure vlan 100 for example on the C2950.

This leaves me with why the link came up as a trunk when the links were connected even though on the C6509, it was never configured as a trunk. I feel as if their side forced the C6509 into trunking.

So if they cannot create any extra vlan on their C2950, how else can I configure this connection as an access port?

amit-singh Wed, 04/05/2006 - 06:27
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********Why the link came up as trunk ? *****

Answer is, 2950 and 6500's support DTP (dynamic trunking protocol ) which means that if either side sends a DTP packet the other side will be able to form a trunk. This is what has happened.

Do the following thing on 2950 switchport :

conf t

int x/y --> port connected to 6500

switchport nonegotiate ** Try this command only first, it should work,if not try other **

switchport mode access

HTH, Please rate if it does.

-amit singh

londint Wed, 04/05/2006 - 06:59
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Thanks Amit.

So after doing this, can we still leave the VLAN as default VLAN 1 at both ends and it wil not trunk?.

amit-singh Wed, 04/05/2006 - 07:04
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yes, You are good to go after that.

HTH, Please rate if it does.

-amit singh

londint Wed, 04/05/2006 - 07:18
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Thank you so very much Amit. I really appreciate your help. I have another question which I will open another message for.

Thanks again.

glen.grant Wed, 04/05/2006 - 07:05
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The 2950 has a default of dynamic desirable on its ports so unless trunking is specifically shutoff on the 6500 it will create a trunk . If the 6500 trunk port is "auto" (default) or desirable the trunk link will come up , just turn the trunk off on the 6500 and the link will not trunk . You can shut it off on the 2950 also by making it an access port also.


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