Add vlan 1 to trunk drops HP switches behind it.

[tbanish730]

I have a 3750 as a core and have a series of HP Procurve switches that are daisy chained using one port.  I have two vlans on the port now (6 &9) and everything works fine, all switches communicate and end devices on the switches are also talking.  There is a requirement to add a device towards the end of the chain which requires it to connect using Vlan1.  Once I add Vlan1 to the port onthe 3750 I lose connectivity to all the HP switches.  Can someone tell me what I'm overlooking?  Thanks!

On the 3750

interface GigabitEthernet1/0/47

description Uplink to HP Switch

switchport trunk encapsulation dot1q

switchport trunk allowed vlan 6,9

switchport mode trunk

On the HP switch, one level down from the 3750.

vlan 1

   name "DEFAULT_VLAN"

   untagged 20-23

   ip address dhcp-bootp

   tagged 24

   no untagged 1-19

   exit

vlan 6

   untagged 1-19

   no ip address

   tagged 21-24

   exit

vlan 9

   ip address x.x.x.x x.x.x.x

   tagged 21-24

   exit

[will.cullen]

On Cisco the Default Native Vlan is 1 so you may want to try and "untag" vlan 1 on the port on the HP switch that connects to the Cisco one, I'm guessing that it may be port 24 by looking at the config you've posted.

[tbanish730]

will - I've tried both tagged and untagged for vlan1 on the HP and get the same results whenever I try to add vlan1 to the 3750. 

j.blakley - when I add vlan1 (switchport trunk allowed vlan1,6,9) I lose connectivity to the HP and all others daisy chained off of it.

Kevin - see my comment to j.blakley.  Trunk on the HP to the 3750 is 22...dooohhh!

Thank you all!  Just figured out that I had the wrong port tagged for Vlan1 traffic on the HP switch.  As soon as I tagged 22 for vlan 1 and added vlan 1 to the 3750 port, I haven't dropped a switch.  Thanks again for helping me see where my mistake was.

[John Blakley]

Tim,

If you just type "switchport trunk allowed vlan 1", it will remove 6 and 9 from the trunk. To add it, type "switchport trunk allowed vlan add 1" and it should be fine.

If you're doing the above, are you wanting to keep vlan 1 as the native? If you need to change the native to something else, type "switchport trunk native vlan ". I know nothing about HP switches, but it looks like above, vlan 1 is going to be untagged on ports 20 - 23. Is that the link that you connected to the Cisco?

HTH,

John

[Kevin Dorrell]

I don't really understand the syntax of your HP switches, but I presume the references on the HP refer to which ports carry the VLAN.  Which port on the HP is your trunk to the 3750?

What command are you using to add vlan 1 to the 3750 G1/0/47 ? It should be switchport trunk allowed VLAN add 1.  If you forget the keyword "add", then you will lose the other VLANs on the trunk, which might explain your symptoms.  Or you can do switchport trunk allowed vlan 1, 6, 9.

Be aware that VLAN 1 will be untagged from the 3750 unless you declare another VLAN as native.

Kevin Dorrell

Luxembourg