I have a few questions regarding STP and L2 security in general.
I read in books that STP sends its BPDU packets via VLAN 1 untagged, but when I used Ethereal sniffer I
found out that BPDU packets are tagged with VLAN for which it sends information about (PVST+).
(i.e for vlan 10 BPDU are tagged with VLAN 10..etc). So when does STP use VLAN 1?
I need two L2 redundant links between two locations. If ISP give me two L2 access port in order to connect
those two loacations would STP work and block one of the links (suppose that I use VLAN 100
on my side and ISP uses VLAN 200 in its core). I tested this scenario in LAB and it works but
I don't know why is it so theoreticaly. I thought that swiches would ignore BPDU-s that come from different VLAN.
UDLD is used if one direction on optical fiber (Rx or Tx) is broken. But if I disconnect from port one of the links, i.e I pull
out RX link and Tx stays in, the ports on both sides of the cable go down. I tested that on new swtiches, but isn't then UDLD feature
sufficient. It seems that ports always go down if only one direction is disconnected so STP can't make a loop.
Were my test an cocnlusion regular?
Thanks in advance,