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New Member

VLAN trunking

I have a 2950T-48-SI, a 3508G-XL, and a 3548-XL.

The 2950T and the 3508 are connected via Gig0/1 on the 2950 and Gig0/7 on the 3508.

The 3548 and the 3508 are connected via Gig0/1 on the 3548 and Gig0/1 on the 3508.

I have been using only the default VLAN for all of my devices. I now want to add a new VLAN (#10) and I want to be able to move each workstation port to a specific VLAN as needed.

Devices on the 2 VLANS do NOT need to communicate with each other and each VLAN has it’s own router.

I’ve created the new VLAN on all switches. The VLAN10 router is connected to the 2950, as is a port in my office. When I assign that port in my office to VLAN10, I get a DHCP address from my VLAN10 router and I get out to the world correctly (through the VLAN10 router and not the VLAN1 router). So I know that the basic VLAN10 is working properly, getting to the correct router, etc.

The problem comes when I try to reconfigure the remote switches (the 3508 and the 3548) to use the new VLAN (in addition to the default VLAN). I can get the 3548 to talk to the 3508 correctly on VLAN10, but I can’t get the 3508 to talk to the 2950 on VLAN10.

The options for Administrative Mode and Administrative Encapsulation on the Gigabit ports are different on the 2950 switch than they are on the 3500XL series, and I guess I don’t know how to set them up correctly.

On the 2950, the only Administrative Encapsulation choice is 802.1Q. The Administrative Mode choices are:

Static Access

Dynamic Access

Dynamic Desirable

Dynamic Auto

802.1Q Trunk

802.1Q Trunk NonNegotiate

On the 3508 and 3548, the only Administrative Encapsulation choice is ISL. The Administrative Mode choices are:

Static Access

Multi-VLAN

Dynamic Access

ISL Trunk

802.1Q Trunk

It seems like the Encapsulation settings should match on both ends, but that doesn’t seem to be possible on these switches …

Can someone help educate me ?

Thanks, Susan

1 ACCEPTED SOLUTION

Accepted Solutions

Re: VLAN trunking

Hi Susan,

The encapsulation settings need not be same through out the network and it should be same on 2 oints connected to each other.

Yes 2950 only supports dot1q

So when you connect 2950T and the 3508 via Gig0/1 on the 2950 and Gig0/7 on the 3508 you can use dot1q encapslation and just issue a command

switchport mode trunk

When you connect 3548 and the 3508 via Gig0/1 on the 3548 and Gig0/1 on the 3508 you can also use dot1q trunk or ISL trunk your wish but better to use dot1q.

config t

interface interface_id

switchport mode trunk

switchport trunk encapsulation dot1q

If you issue this config on all the switches connected to each other it should definetely form a trunk.

Only thing is when you put this commands on 2950 switch need not put dot1q as it only supports dot1q

config t

interface interface_id

switchport mode trunk

HTH, if yes please rate the post.

Ankur

2 REPLIES

Re: VLAN trunking

Hi Susan,

The encapsulation settings need not be same through out the network and it should be same on 2 oints connected to each other.

Yes 2950 only supports dot1q

So when you connect 2950T and the 3508 via Gig0/1 on the 2950 and Gig0/7 on the 3508 you can use dot1q encapslation and just issue a command

switchport mode trunk

When you connect 3548 and the 3508 via Gig0/1 on the 3548 and Gig0/1 on the 3508 you can also use dot1q trunk or ISL trunk your wish but better to use dot1q.

config t

interface interface_id

switchport mode trunk

switchport trunk encapsulation dot1q

If you issue this config on all the switches connected to each other it should definetely form a trunk.

Only thing is when you put this commands on 2950 switch need not put dot1q as it only supports dot1q

config t

interface interface_id

switchport mode trunk

HTH, if yes please rate the post.

Ankur

New Member

Re: VLAN trunking

Ankur -

These configuration settings got the trunks passing correctly. Thanks a bunch!

Unfortunately, now I have another problem. Since it occurred just after I configured the trunking, seems like it must be related. I will start a new thread for that one (it's an error message about the redundant power supply).

Thanks again, Susan

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