Failing to VLAN a fibre link correctly.

Unanswered Question
May 3rd, 2007


I have been tasked with setting up a small network within our company. The network is to utilise some existing fibre links but to stay seperate in terms of connectivity/reachability etc. Therefore I am trying to VLAN one of our cross site fibre links ( in a lab env at present )

My idea is to configure an existing fibre link to trunk 2 vlans instead of just the one native vlan it has at the moment. These are HP procurves so I have left the native VLAN as untagged and tagged my vlan for these purposes. At eihter end of the link I have taken one port and assigned it to my static VLAN only (i.e no default vlan connection and UNTAGGED for my vlan traffic) I believe this to be working ok but I am having trouble when I patch in my 2 Cat2950 switches. I would assume that because I have marked the traffic as untagged coming out the procurves to the switches that there would be no tagging/VLAn info on it when it reached the Cisco. However the port never comes up. It complains of:

1.Inconsistent BPDU packets

2.Inconsistent VLAN 1's

Therefore it keeps the ports shut.

The only way to bring the put up is to unpatch the cross fibre link and this informs me that "port consistency" has agin been achieved.

Am I not correct in assuming that the VLAN info should have been stripped out by the time it reaches the Cisco's

Also, why would the 2950 complain abot inconsisten VLANs ? I would have thought it would not be able to see the native vlan on the procurve seeing I have statically mapped it to a seperate vlan?

I would also have thought that i could have left the CAt2950 in its management vlan and set as access, not trunk,seeing as all vlan traffic reaching it has info stripped out.

Any ideas or smarter ways of doing this greatly appeciated...



I have this problem too.
0 votes
  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 0 (0 ratings)
jonathanaxford Wed, 05/09/2007 - 09:10


Not quite sure WHERE the Cisco boxes fit in...

You have 2 procurve devices, one at each end of a fibre link, and you have created a seperate VLAN on each one of these Switches, tagged the link over the fibre and created 2 untagged ports in that seperate VLAN, one at each end...

Is that correct? Are you then plugging the Cisco Devices into this VLAN?

If this is the case, i would Tag the links to the Cisco boxes, at each end and only allow the trunk to carry the correct VLAN, thereby keeping it seperate?

If could clarify how you have the network phsyically setup?

Also, what version of STP are you running? What are the HP switches?

A 'native' VLAN will not have the 802.1q tag applied to it, by default this will be VLAN 1 on both the Cisco and HP devices...


This Discussion