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New Member

Spanning Tree problem...

I have a pair of Alcatel core switches. I have enabled STP and set the priorities to 8000 and 16000. All other switches in the LAN our set to the default 32768. Most of the other switches in the LAN are 3500XL's. We also have two 4507's for our server farm. Each of these switches only have 1 link back to the core.

This morning I connected a new switch to the core. This switch is connecting via a 802.1q trunk. After connecting this switch everything was fine but then the two 4507's went into to block mode. The log said a 802.1q bpdu was received on the non-trunk port.

My question is why did this happen? I thought all bpdu's flowed toward the root, which in my case would be the core switch. In my mind the 4507's are connected the same way that any other 3500XL switch is to the core and they didn't go into a block state.

I did notice that uplinkfast was configured on the 4507's. I removed that from both.

Any ideas?

Thanks

  • Other Network Infrastructure Subjects
8 REPLIES

Re: Spanning Tree problem...

Hi,

what's the topology?

Are you connecting the new switch to the core Alcatel switches or to the 4507?

Are all the switches connected via trunks?

Are the native VLANs the same on all trunks?

Regards,

Milan

New Member

Re: Spanning Tree problem...

everything connects to the core alcatel. the 4507s connect to the core and the 3524 connects to the core.

only the new 3524 is connected via a trunk.

the native vlans are not the same on all trunks. this is due to an incompatibility of the alcatel switch. vlan 1 is native and you cannot change it.

i was able to replicate this problem in my lab. in the lab i have a core alcatel switch. if i connect a 3524 to one link (non-trunk) then connect another 3524 (trunk) to another port on the alcatel everything is fine. but if i connect a 2950 (non-trunk) to the core then connect the 3524 (trunk) the 2950 temporarily goes into a block state. i have tried disabling dtp on the 2950. i have set it to off mode so it won't try to trunk. it still blocks. and this is what happened on the 4507's.

i have a tac case open and our local ccie rep looking at it and they're both stumped.

Bronze

Re: Spanning Tree problem...

My new 2950s have some new defaults related to spanning tree.

spanning-tree mode pvst

no spanning-tree optimize bpdu transmission

spanning-tree extend system-id

I believe they are cisco features that may not be supported by the Alcatel and might be causing some confusion between the switches.

New Member

Re: Spanning Tree problem...

my 2950 and 4507s don't have those defaults.

i am positive my problem is due to vendor incompatibility. the question now is what do i do? the resolution i am pushing for from my company is to junk the alcatel and get some 6509s :)

Re: Spanning Tree problem...

What is the exact error message?

It that non-trunk port asigned to VLAN1? Or any other VLAN? Is the 2950 connected only via this one port to the network or are there any other ports connected to other switches?

Is the native VLAN setting on the trunk correct? Are you sure Alcatel switch does support native VLAN feature, i.e. native VLAN (VLAN1) frames are sent not tagged?

It seems to me like vendor incompatibility problem, but the Alcatel switch should not send 802.1q tagged frames to non-trunk port. I would try to connect a data analyzator to the non-trunk line to see what's coming.

Regards,

Milan

New Member

Re: Spanning Tree problem...

the error message that the 2950 receives is "received 802.1q bpdu on non-trunk port x". the 2950 has only one link to the core and no other connections out.

i need to keep vlan 1 up for data connections while migrating into other vlans.

i have not put an analyzer on the link yet, but i believe that the alcatel is tagging vlan 1. the 3524 don't tag it unless i specify the native vlan as something besides 1. and then the alcatel don't let you specify the native to anything but vlan 1. so it does seem that i am basically stuck now due to the incompatibility.

thanks

Re: Spanning Tree problem...

Hi,

I don't understand why the Alcatel switch is tagging VLAN1.

If the port is non-trunk on the 2950 side it should be configured as non-trunk on Alcatel side either and no tagging should be applied at all.

It seems like Alcatel switch is trunking 802.1q on the port.

See http://cco-rtp-1.cisco.com/en/US/customer/products/hw/switches/ps628/products_system_message_guide_chapter09186a00800d8194.html#xtocid13 :

"Error Message SPANTREE-7-RECV-1Q-NON-TRUNK: Received 802.1Q BPDU on non trunk [chars] [chars].

Explanation This message means that an SSTP BPDU was received on the listed interface, which is not an operational trunking interface. The first [chars] is the port name, and the second [chars] is the VLAN name.

Recommended Action Verify that the configuration and operational state of the listed interface and that of the interface to which it is connected are in the same mode (access or trunk). If the mode is trunk, verify that both interfaces have the same encapsulation (none, ISL, or 802.1Q). When these parameters are consistent, spanning tree automatically unblocks the interface."

Regards,

Milan

New Member

Re: Spanning Tree problem...

The Alcatel is forwarding VLAN 999 BPDU's to the 2950 and it is blocking because of that. I have to set the native VLAN between the core Alcatel and the 3524 to 999 so it will tag VLAN 1.

I am giving up on getting this to work. I have to implement way too many work arounds just to get this working that it's not worth the trouble anymore.

Thanks for your help.

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