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3560+2950

hi! i'm planning to connect a L3 (3560sw) to a L2 2950 switch with multiple vlans configured. My question is that, with the default setting, must i issue a "switchport mode trunk" for both of the switches' interconnected port? or will both the ports autonegotiate by itself to create a trunk? Must i configure encapsulation dot1q in this case?

For intervlan routing, apart of issueing the "IP routing" command on the L3 switch + setting ip for each of the vlan interface created, do i need to run any routing protocol or static route to do the vlan routing within these few vlan interfaces?

Thanks.

5 REPLIES
Hall of Fame Super Blue

Re: 3560+2950

Hi David

It is good practice to explicitly configure your trunk ports with the "switchport mode trunk" command.

On the 2950 the only encapsulation available is 802.1q so you do not need to specify it but you should on the 3560.

Just enabling ip routing will be enough and setting up the layer 3 SVI's will be enough as the 2950 will be running as a layer 2 device only.

HTH

Jon

Community Member

Re: 3560+2950

hi! Will the default port config auto negotiate a trunk automatically when both the L3 and L2 switches is connected with a cross cable?

Purple

Re: 3560+2950

If the 3560 port is set as a switchport then both should negotiate the trunk as I believe the default on these devices is to have the port set as "dynamic desirable " which will negotiate a trunk correctly . It is always good practice to manually prune off all other vlans that are not needed on the trunk link . Everyone has there own opinions but as far as trunk links go and from the cisco docs I have read it is better to let the switches negotiate the trunk as opposed to forcing the trunk on with the switchport mode trunk command .

Community Member

Re: 3560+2950

hi! for vtp to work, is it a must to enable trunking and encapsulation between 2 switches?

Community Member

Re: 3560+2950

I am also trying to connect a 24 port 2950 to a 24 port 3560 switch using a crossover cable between port 24 on each. I have tried using the following commands via hyper terminal: 2950:

int FA0/24

speed 100

duplex full

no snmp trap link-status

no logging event link-status

switchport mode trunk

!

and 3560:

interface FastEthernet0/24

switchport trunk encapsulation dot1q

switchport mode trunk

no logging event link-status

speed 100

duplex full

no snmp trap link-status

!

However, about 20-30 seconds after I connect the crossover cable, the used port LED's on the 3560 switch blink 4-5 times per sec, vs ~1 per second with the cable disconnected, as if it has far more traffic. This causes issues with our devices. Can anyone tell me if this is the correct way to do what I am trying to do, or is there a better way? I also have the network assistant, but am unclear where/how to make the proper changes. Any help would be appreciated.

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