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How do I trunk a Cisco 2950 to a Cisco 3550 switch

Posted on 2009-04-09
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Last Modified: 2012-05-06
I am adding an additional network at my office.  The new network is going to be on a cisco 2950 switch that is connected to a "Layer 3" Cisco  3550 switch.  I have the ports on the 2950 going to the 3550 set as "switchport mode trunk".  On the 3550, I have the port configured with "switchport trunk encapsulation dot1q"  I can't get these two switches to communicate.  Any Ideas?
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Question by:Crossroads305
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by:atlas_shuddered
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On all ports:

switchport trunk encapsulation dot1q
switchport mode trunk

If I read the above right you have half the answer on each port.

Cheers
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by:Crossroads305
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Thanks.  On the 2950, the command "switchport mode trunk" works, but "switchport trunk encapsulation dot1q" does not.  It will work on the 3550?
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by:Crossroads305
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Any other ideas?
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by:atlas_shuddered
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Sorry - 2950 only supports dot1q so you won't have to run the command on its interface.

Use both commands on the 3550 ports.
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by:Crossroads305
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Still not working.  My 3550 is a 10 port fiber switch.  I have run the command "switchport trunk encapsulation dot1q" on the 3550 for the port that the 2950 connects to.  I still can't communicate between switches
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by:atlas_shuddered
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Can you post a config of both?
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by:Crossroads305
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First config is the 2950.  Second config is the 3550.  The 2950 connects to int gigabitethernet 0/7 on the 3550.

version 12.1
no service pad
service timestamps debug uptime
service timestamps log uptime
service password-encryption
!
hostname 2950
!
clock timezone est -5
clock summer-time EDT recurring 2 Sun Mar 2:00 1 Sun Nov 2:00
ip subnet-zero
!
!
spanning-tree mode pvst
no spanning-tree optimize bpdu transmission
spanning-tree extend system-id
!
!
!
interface FastEthernet0/1
!
interface FastEthernet0/2
!
interface FastEthernet0/3
!
interface FastEthernet0/4
!
interface FastEthernet0/5
!
interface FastEthernet0/6
!
interface FastEthernet0/7
!
interface FastEthernet0/8
!
interface FastEthernet0/9
!
interface FastEthernet0/10
!
interface FastEthernet0/11
!
interface FastEthernet0/12
!
interface FastEthernet0/13
!
interface FastEthernet0/14
!
interface FastEthernet0/15
!
interface FastEthernet0/16
!
interface FastEthernet0/17
!
interface FastEthernet0/18
!
interface FastEthernet0/19
!
interface FastEthernet0/20
!
interface FastEthernet0/21
!
interface FastEthernet0/22
!
interface FastEthernet0/23
!
interface FastEthernet0/24
!
interface GigabitEthernet0/1
switchport mode trunk
!
interface GigabitEthernet0/2
switchport mode trunk
!
interface Vlan1
 ip address 10.0.32.2 255.255.240.0
 no ip route-cache
!
ip default-gateway 10.0.32.1
ip http server
!

!
!
end

Cisco 3550

Building configuration...

Current configuration : 3071 bytes
!
version 12.1
no service pad
service timestamps debug uptime
service timestamps log uptime
no service password-encryption
!
hostname 3550
!
no logging console
!
clock timezone EST -5
clock summer-time EDT recurring 2 Sun Mar 2:00 1 Sun Nov 2:00
ip subnet-zero
ip routing
!
!
spanning-tree mode pvst
spanning-tree extend system-id
!
!
!
interface GigabitEthernet0/1
 no ip address
!
interface GigabitEthernet0/2
 no ip address
!
interface GigabitEthernet0/3
 no ip address
!
interface GigabitEthernet0/4
 no ip address
!
interface GigabitEthernet0/5
 no ip address
!
interface GigabitEthernet0/6
 no ip address
!
interface GigabitEthernet0/7
 switchport trunk encapsulation dot1q
 no ip address
!
interface GigabitEthernet0/8
 no ip address
!
interface GigabitEthernet0/9
 no ip address
!
interface GigabitEthernet0/10
 no ip address
!
interface GigabitEthernet0/11
!
interface GigabitEthernet0/12
 no ip address
!
interface Vlan1
no ip addresss
!
interface Vlan2
 no ip address
!
interface Vlan20
 description TEST
 ip address 10.0.32.1 255.255.240.0
!
interface Vlan30
 no ip address

end

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Expert Comment

by:Don Johnston
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Please post the output of a "show int status" for both switches.


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atlas_shuddered earned 500 total points
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On the 3550:

int gig 0/1
no shut
switchport mode access

int gig 0/7
switchport mode trunk
no shut

int vlan 20
no ip address 10.0.32.1 255.255.240.0

int vlan 1
ip address 10.0.32.1 255.255.240.0
no shut


on 2950

int fast 0/1
no shut
switchport mode access

int gig 0/1
no shut

int gig 0/2
no shut

int vlan 1
no shut


Right now you have your IP's set up in two different vlans so ping is not going to work.  Connect a PC to the access interfaces on each of the switches and test your ping.

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Author Closing Comment

by:Crossroads305
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Thanks, I can't believe I overlooked that.   I put them both in the same vlan and was then able to pass traffic with no problem
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