Interesting problem, I'll try to keep it simple :
1. Two sites in two different locations, interconnected by X-Connect via 6800 links. One site has tens of hosts and some switches, the other remote site is small with one switch and a few hosts. The sites are connected by a single link.
2. Both sites have 4948 switches with STP/BPDU guards and loop guards enabled as well as storm control.
3. When connecting the ports on both ends with any config (access or trunk) that does not involve VLAN1 all is well.
4. When defining VLAN1 on the ports in either access or trunk mode - once connected, traffic goes down on ALL ports on one side for about 10 seconds, then comes back.
5. No loops exists. Furthermore, on the end with the single switch and few hosts - even if all ports are shut down and only one port is left for the inter-site connection, the phenomena occurs - so it's not some mac flooding between sites.
6. The phenomena seems to occur with any piece of network equipment connected to any port on the 4948 - once connected, all traffic drops for 10 seconds.
We tried enabling and disabling all bpdu etc and stp and tried playing around with any possible config but this issue still persists. Any network device with VLAN1 enabled on the port that is connected to the 4948 causes all traffic to be dropped for 10 seconds.
And...of course... nothing is logged in the log.
