MSTP Setup across sites

[oysterman]

Hi All,

I have 2 x 2510G-48 switches on site 1, with multiple VLANS duplicated on both switches.

The 2 switches are linked together via 1 Cat6 cable (port 45) which is tagged in all VLANS so that traffic can pass between the switches.

Each VLAN has untagged ports configured, with port 45 (dual personality port) tagged in each VLAN.

I enabled spanning tree on both switches and basically left the rest of the configurations at default.

All this is working fine.

I have exactly the same setup at site 2. Although I have named the VLANS at site 2 the same as site 1, the devices at site 2 all have different IP addresses.

We have just purrchased a layer 2 ethernet connection which is going to be used to link 1 switch at site 1, with 1 swtich at site 2.

To do this I have configured a new VLAN on each of the switches and defined the ports as untagged. I then connected the ethernet circuit into switch 1/site 1 and into switch1/site 2.

I was able to see devices across the new link so I thought all was ok.

A few hours later, the connection between sites was interupted for approx 30 - 60 seconds and then everything recovered.

The logs on one of the switches displayed the  following message :

I 01/21/91 07:18:04 stp: CIST starved for a BPDU Rx on port 36 from 32768:b439d6-983f40
I 01/21/91 07:18:04 stp: CST Root changed from 32768:b439d6-983f40 to 32768:f06281-441980
I 01/21/91 07:18:04 stp: CST Root changed from 32768:f06281-441980 to 32768:b439d6-983f40

I have no idea why this happened?

One thing I have thought of doing is disabling spanning tree on the ports this connection uses (as there won't be any loops as its simply 1 switch to the other). I was going to do this using the bpdu-filter command on the particular ports on the 2 switches. Will this stop the type of disconnection seen above?

My thoughts are that something happened which caused spanning tree to re-evaluate its settings, causing a brief disconnection on the ports linking the 2 sites together. As I am relying on this connection between sites to stay up all the time, if I disable spanning tree on these ports will that stop spanning tree from interfering with this link?

What do you think?

Thanks

John

[oysterman]

Is anyone there???