cancel
Showing results for 
Search instead for 
Did you mean: 
cancel
1848
Views
0
Helpful
6
Replies

Setting second 4500 as root bridge for odd VLANS

Alan Taylor
Level 1
Level 1

Hi all,

I'm hoping someone can offer me advice or an answer to my problem.

I've been trying to set switch B (A --- B trunked) to be the root bridge for numerous VLANs in my development network.

I'm pretty sure I should accomplish this by ensuring the relevant spanning-tree priority is set low i.e.

Switch B

interface vlan 3

<snip>

end

!

spanning-tree vlan 3 priority 4096

Switch A

interface vlan 3

<snip>

end

!

spanning tree vlan 3 priority 8192

however when I change the priority of Switch B the trunk I use to connect via telnet goes down following an error on Switch A of :

SPANTREE-2-PVSTSIM_FAIL: Blocking designated port....

This occurs if I change switch A priority first or not... I've waited a few minutes for the trunk to stop blocking without joy so I'm putting the question here for help.

breifly the setup is

PC--1Gb--Switch A--Trunk--SwitchB

I can connect via console on Switch B and CDP packets are passing between the devices (the trunk native vlan differs from the vlan in question) but not see any of the vlan interface present on Switch A and vice versa.

Thanks in advance

- Sudo.

1 Accepted Solution

Accepted Solutions

Hi Pseudopath,

Firstly, is this a mixed-Vendor environment?  This sounds similar to an issue I've come across previously with Cisco not playing nice with other spanning-tree devices - Per-VLAN spanning-tree is Cisco Proprietary so other vendors only support STP, RSTP and MST

Second, are you running rapid, or regular Per-Vlan Spanning Tree?

I'd definately recommend setting rapid on both switches by doing a


(config)#spanning-tree mode rapid-pvst

It's backwards compatible with regular PVST, so don't worry if all your switches aren't set the same right off the bat, but you should eventually get round all your devices and set this.

Next, try this:

Switch1(config)#spanning-tree vlan 1-4094 root primary


Switch2(config)#spanning-tree vlan 1-4094 root secondary

Switch2(config)#spanning-tree vlan 3 root primary


Switch1(config)#spanning-tree vlan 3 root secondary

I just tested this on my 6500s and it works fine - If you get an issue with the link going down again, on switch 1 do a "show spann vl 3"  and see where it thinks the root bridge is... it should come back with the mac address of switch 2 - if not there's some other device on the network that is somehow claiming root - you can find it by following the root ports for that VLAN.

Failing that, can you post here the interface configs on both ends of your Switch1 - Switch2 Interlink?

Nick

View solution in original post

6 Replies 6

jonathanaxford
Level 3
Level 3

Hi Sudo,

This may seem like a vey silly question, but does VLAN 3 itself exist on the switch as well as the VLAN 3 interface? I have seen it before where the Layer 3 VLAN interface exists, but there is no VLAN in the VLAN database that matches!

Cheers

Jonathan

Hiya Jonathan,

Thanks for your reply.

As far as I am aware the vlan database should be configured with vlan3, I've set up a VTP domain etc and I know that's working after lots of minutes scratching my head to realise "transparent" does wot it says on the tin... anyway I cant check atm as Im not able to access the devices but I am pretty sure its there.

Thanks,

- Sudo.

Okely dokely, I've checked both switches and the "show vlan brief" command displays vlan3 as active.

I'm still bemused at the moment I'm afraid so any advice/remarks would be welcome.

- Sudo.

Hi Pseudopath,

Firstly, is this a mixed-Vendor environment?  This sounds similar to an issue I've come across previously with Cisco not playing nice with other spanning-tree devices - Per-VLAN spanning-tree is Cisco Proprietary so other vendors only support STP, RSTP and MST

Second, are you running rapid, or regular Per-Vlan Spanning Tree?

I'd definately recommend setting rapid on both switches by doing a


(config)#spanning-tree mode rapid-pvst

It's backwards compatible with regular PVST, so don't worry if all your switches aren't set the same right off the bat, but you should eventually get round all your devices and set this.

Next, try this:

Switch1(config)#spanning-tree vlan 1-4094 root primary


Switch2(config)#spanning-tree vlan 1-4094 root secondary

Switch2(config)#spanning-tree vlan 3 root primary


Switch1(config)#spanning-tree vlan 3 root secondary

I just tested this on my 6500s and it works fine - If you get an issue with the link going down again, on switch 1 do a "show spann vl 3"  and see where it thinks the root bridge is... it should come back with the mac address of switch 2 - if not there's some other device on the network that is somehow claiming root - you can find it by following the root ports for that VLAN.

Failing that, can you post here the interface configs on both ends of your Switch1 - Switch2 Interlink?

Nick

Hi,

Could you please tell me whether you are using MST in either of the switches or not. Please attach the entire running configuration from both the switches( after removing the IPs obviously).

Rgds,

Souvik

Hi there Nick,

Thanks very much for the advice regarding the rapid spanning-tree. My environment does include a HP C7000 chassis but I had already enable bpdu guard on the appropriate ports.

On reflection it may be that the synchronisation was taking longer than I was waiting with PVST.

Once I had enabled RPVST on both switches and followed the process you suggested (which is roughly how I was configuring it previously) all is working how I wanted it. Great news, thank you.

Also, thanks to Souvik for taking the time to post.

I'm pleased as punch!

- Sudo.

Getting Started

Find answers to your questions by entering keywords or phrases in the Search bar above. New here? Use these resources to familiarize yourself with the community:

Innovations in Cisco Full Stack Observability - A new webinar from Cisco