2950---trunk----2950 is it possible?

[benrondina]

Can I take two 2950 switches and build a vlan trunk between them? I have three vlans on each switch and each vlan is a subnet.

[paddyxdoyle]

Yes,

The config on both switches will be something like:

int fa 0/24

switchport mode trunk

switchport trunk encapsulation dot1q

switch trunk allowed vlan 1,2,3

HTH

PJD

[benrondina]

switchport trunk encapsulation dot1q not a menu option. Maybe I need to add something first?

[benrondina]

please see picture attached.

My 2900's dont have the menu item to trunk encapsulatation dot1q. Maybe I have to change the ios or configure something first.

[carl_townshend]

"switch trunk allowed vlan 1,2,3"

Do you need to put this on any switch config to allow the other vlans through ? if not will it not let them thorugh until you specify ?

[glen.grant]

You don't have to put this in because by default all vlans are allowed across the trunk, it is good practice to prune off unused vlans , it reduces spanning tree instances , provides some security by not allowing other vlans across and reduces a little of the load on the switch due to spanning tree reduction .

[thisisshanky]

You can do as many as 1024 vlans on a switch and trunk them across to another switch. So this is possible. THe question is who will route between these subnets. YOu will have to use either a layer 3 switch (2950s are layer 2) or an external router (router on a stick configuration) to route between these subnets.

Using layer 3 switch:-

http://www.cisco.com/en/US/tech/tk389/tk815/technologies_configuration_example09186a008015f17a.shtml

Using external router-

http://www.cisco.com/en/US/tech/tk389/tk390/technologies_configuration_example09186a00800949fd.shtml

HTH

[thisisshanky]

2950 supports only dot1q encapsulation. It does not support ISL. So all you need to do is,

int fa0/1

switchport mode trunk

It defaults to DOT1q

[benrondina]

I cannot pass traffic from one switch to the other except on vlan 1. No other vlans will pass traffic between switches. pc's in vlan 10 between each switch will not communicate. Trunk is established and up and pc's in vlan 1 will talk between switches. ??help??

[paddyxdoyle]

Can you paste the output of the following on both ends of the trunk:

# show interface switchport

i don't think your switch supports the following but try anyway

# show interface trunk

Thanks

Paddy

[buchholr]

Most likely the other vlans have not been added to the switch. Even if they are assigned to an interface, the switch will not create the vlan, and will not run a spanning tree instance for it. Vlan 1 works because it is the default vlan and always exists on the switch.

The command to check for this issue is:

#show spanning-tree vlan 20

If the switch returns an error, you need to add the vlan.

The command to add a vlan is simply:

(config)#vlan vlan_no

So a complete config on each switch would look like this (assuming you are trunking on interface 0/1):

switch#configure terminal

switch(config)#vlan 10

switch(config)#vlan 20

switch(config)#interface FastEthernet 0/1

switch(config-if)#switchport mode trunk

switch(config-if)#switchport trunk allowed vlan 1,10,20

switch(config-if)#end

switch#copy running-config startup-config

Hope this helps

Robert