CAT VLAN Trunking

[micon55]

I am in the process of configuring a CAT 4000 switch as a VTP server with trunk links feeding some CAT 2950 switches.

When I check the spantree on the 4000, both my trunk links are forwarding OK. The problem is that my 2950 switches are showing spantree errors and I am unable to bring both VLAN 1 and VLAN 2 up together. As soon as I bring one VLAN up the other goes down.

Any help much appreciated.
M

 

[scraig84]

Knowing what errors you are getting may help a bit.

Have you done any Spantree configuration to set which switch is root etc? If the 4000 is the central switch, you may want to adjust the priority of the 4000 down to a real small number (like 10) for each VLAN to ensure that it becomes the root.

 

[micon55]

Thanks for the reply.
I've set VLANs 1 and 2 on the CAT 4000 switch to a low spantree priority.
I've even disconnected the 2950 switch and changed it's vtp mode to transparent, yet I'm still unable to bring both VLAN1 and VLAN2 up together.

I've not seen anything this weird before...

 

[wybnormal]

Let me ask a question, is this your map?

2900 4000
|--------vlan1--------|
|--------vlan2--------|
| |

In otherwords, are the two vlans coming off a single 2950? across two links? or are these two vlans trunked across a single link?

VTP server/client has nothing to do with spanning tree protocol. VTP manages VLANs not spantree. If you do a show spantree(Ithink that the command on a 4K) on the Cat4K, does it should ports disabled?

MikeS


Find me at

http://www.packetattack.com

"Take advantage of the enemy's unreadiness, make your way by unexpected routes, and attack unguarded spots."
Sun Tzu

 

[micon55]

The configuration you've drawn is exactly how we WANT it to work, with 2 fibre links carrying 2 seperate VLANS. I have tried lots of different configurations without success.
Currently, I am trying to configure a GigaEtherChannel link as advised by Cisco. Alas, not much info on the Web about this.
All I want to do is have 2 VLANS on the CAT 4000 switch. These 2 VLANS can then be carried to the 2950 switch via 2 fibre links. Then I want to assign the ports on the 2950 to their respective VLAN.
Trouble is, even when I disconnect the 2950 switch and make it transparent, I STILL can't bring VLAN1 and VLAN2 up at the same time.

Any ideas much appreciated.....Hair is being pulled as I speak!!

 

[wybnormal]

2912 Cat5K
|---------trunk--------|
|---------trunk--------|



I'll bet it has to do with your trunk configuration. See the long clip below. it's a 2912 and a cat5K but should be close enough. Without the links being trunks(which require the administrative VLAN which also carries the STP), it works fine. VLAN 100 is on ports SW2 0/1 and C1 3/1. VLAN 200 is one ports SW2 0/2 and C1 3/2. With vlans created and spanning tree enabled, the links come up fine. Keep in mind, no VTP which requires a trunk and admintrative VLAN.

Even with trunks enabled, as long as I have different native VLANs, it comes up as it should.


The difference is I can not do 802.1Q on my cat5K.

MikeS


Console> (enable) sho trunk
* - indicates vtp domain mismatch
Port Mode Encapsulation Status Native vlan
-------- ----------- ------------- ------------ -----------
3/1 on isl trunking 100
3/2 on isl trunking 200

Port Vlans allowed on trunk
-------- ---------------------------------------------------------------------
3/1 2-199,201-1005
3/2 2-99,101-1005

Port Vlans allowed and active in management domain
-------- ---------------------------------------------------------------------
3/1 100
3/2 200

Port Vlans in spanning tree forwarding state and not pruned
-------- ---------------------------------------------------------------------
3/1 100


Console> (enable) sho spantree 3/1
Port Vlan Port-State Cost Priority Portfast Channel_id
------------------------ ---- ------------- ----- -------- ---------- ----------
3/1 100 forwarding 19 32 disabled 0


Switch#sho span inter fa0/1
Interface Fa0/1 (port 13) in Spanning tree 100 is FORWARDING
Port path cost 19, Port priority 128
Designated root has priority 32768, address 00d0.58b6.8981
Designated bridge has priority 32768, address 00d0.58b6.8981
Designated port is 13, path cost 0
Timers: message age 0, forward delay 0, hold 0
BPDU: sent 197, received 717
Switch#
Switch#sho span inter fa0/2
Interface Fa0/2 (port 14) in Spanning tree 200 is FORWARDING
Port path cost 19, Port priority 128
Designated root has priority 32768, address 00d0.58b6.8982
Designated bridge has priority 32768, address 00d0.58b6.8982
Designated port is 14, path cost 0
Timers: message age 0, forward delay 0, hold 0
BPDU: sent 187, received 748
Switch#


------------ CAT 5K config --------------
!
# ***** NON-DEFAULT CONFIGURATION *****
!
!
#time: Thu Jun 20 2002, 15:51:35
!
#version 5.5(13a)
!
!
#test
set test diaglevel complete
!
#frame distribution method
set port channel all distribution mac both
!
#vtp
set vtp domain test
set vlan 1 name default type ethernet mtu 1500 said 100001 state active
set vlan 100 name VLAN0100 type ethernet mtu 1500 said 100100 state active
set vlan 200 name VLAN0200 type ethernet mtu 1500 said 100200 state active
set vlan 1002 name fddi-default type fddi mtu 1500 said 101002 state active
set vlan 1004 name fddinet-default type fddinet mtu 1500 said 101004 state activ
e stp ieee
set vlan 1005 name trnet-default type trbrf mtu 1500 said 101005 state active st
p ibm
set vlan 1003 name token-ring-default type trcrf mtu 1500 said 101003 state acti
ve mode srb aremaxhop 7 stemaxhop 7 backupcrf off
!
#ip
set interface sc0 1 192.168.100.100/255.255.255.0 192.168.100.255

!
#spantree
#vlan <VlanId>
set spantree portcost 1003 80
!
# default port status is enable
!
!
#module 1 : 2-port 100BaseTX Supervisor
!
#module 2 : 12-port 10/100BaseTX Ethernet
!
#module 3 : 12-port 10/100BaseTX Ethernet
set vlan 100 3/1
set vlan 200 3/2
clear trunk 3/1 1,200
set trunk 3/1 on isl 2-199,201-1005; clears VLAN 1 & 200 from trunk
clear trunk 3/2 1,100
set trunk 3/2 on isl 2-99,101-1005; clears VLAN 1 & 100 from trunk
!
#module 4 empty
!
#module 5 empty
end
Console> (enable) Find me at

http://www.packetattack.com

&quot;Take advantage of the enemy's unreadiness, make your way by unexpected routes, and attack unguarded spots.&quot;
Sun Tzu

 

[tuks]

Im just doing some reading and found out that ISL wont work on 2950. It only supports 802.1Q. Could be a difference in trunking protocol. Correct me if Im wrong, what I understand is that both trunk ports must use the same trunking protocol. I havent done this in reality before but check it out. This could contribute to your problem

Good luck

 

[micon55]

Thanks for your help guys. In the end I created a port channel and allowed VLANs from the 2950 switch onto each port link. Seems to be working OK.

I do have one other problem though. How can I get a GB fibre module on a CAT 4000 to successfully communicate with a 100MB uplink port on an older 2924 switch.

I have set up the uplink ports as trunks and set the encapsulation to match.
Do I need to enable auto negotiation on my 4000?

Many thanks
M

 

[BuckWeet]

As for the GB Fiber Module to the 2924, won't work, the GB's only run at 1000BaseSX or LX, whichever you have..


BuckWeet