Options
Windows 7 Can Participate in STP
theodoxa
Member Posts: 1,340 ■■■■□□□□□□
in CCNA & CCENT
I decided to hook my Cisco 2960 switches up to my home network. For now, [as there is no physical cable to the room where my lab is] I am using a PC running Windows 7 Professional to act as a wireless bridge. I have the 802.11n Wi-Fi NIC bridged to a Gigabit Wired NIC using Windows' MAC Bridge feature. The wired NIC is connected to a small unmanaged Gigabit switch.
I trunked the switches together and then connected SW2's GigabitEthernet 0/2 to the unmanaged Gigabit switch. I configured each switch using a Console cable. I assigned IP Addresses to the VLAN 1 interfaces and configured them to allow SSH access via the vty lines and then I disconnected from the Console and connected via SSH from my laptop.
I decided to configure them to use Rapid STP. Then, I typed "sh span" and the switch I was connected to was not the root bridge. So, I SSHed into SW2 and ran "sh span". It was no the root bridge either. Gi0/2 (the one connected to my home network) was listed as a "Root Port" and when I ran "sh mac address-table" the MAC Address of the root bridge was indeed listed off Gi0/2. This left 3 interesting possibilities as to who the root bridge was [since it was NONE of the Cisco switches]:
1) The unmanaged switch - highly unlikely
2) The Windows 7 PC (MAC Bridge)
3) The Home Router's Built-In Switch
Initially, I logged into the home router, but couldn't find any way to display its MAC Address. So, I connected to the Windows 7 PC via Remote Desktop and ran "ipconfig /all". I figure if it wasn't the root bridge, I would have been able to check the ARP Cache and see which interface the culprit MAC was connected to (either the one facing the router or the one facing the unmanaged switch). But, as luck would have it, the MAC Address of the Windows 7 PC matched the one listed in the "sh span" command. It was the root bridge. I decided to Google it and another person had posted about the same thing: A Windows 7 PC sending out BPDUs after bridging its interfaces. It appears, Windows 7 supports Spanning-Tree and in fact even been elected ROOT BRIDGE [M$ appears to use the same default priority as Cisco, so MAC Address was the tie breaker - The PC's was lower], which makes sense as bridging interfaces introduces the possibility of creating a switching loop.
I trunked the switches together and then connected SW2's GigabitEthernet 0/2 to the unmanaged Gigabit switch. I configured each switch using a Console cable. I assigned IP Addresses to the VLAN 1 interfaces and configured them to allow SSH access via the vty lines and then I disconnected from the Console and connected via SSH from my laptop.
I decided to configure them to use Rapid STP. Then, I typed "sh span" and the switch I was connected to was not the root bridge. So, I SSHed into SW2 and ran "sh span". It was no the root bridge either. Gi0/2 (the one connected to my home network) was listed as a "Root Port" and when I ran "sh mac address-table" the MAC Address of the root bridge was indeed listed off Gi0/2. This left 3 interesting possibilities as to who the root bridge was [since it was NONE of the Cisco switches]:
1) The unmanaged switch - highly unlikely
2) The Windows 7 PC (MAC Bridge)
3) The Home Router's Built-In Switch
Initially, I logged into the home router, but couldn't find any way to display its MAC Address. So, I connected to the Windows 7 PC via Remote Desktop and ran "ipconfig /all". I figure if it wasn't the root bridge, I would have been able to check the ARP Cache and see which interface the culprit MAC was connected to (either the one facing the router or the one facing the unmanaged switch). But, as luck would have it, the MAC Address of the Windows 7 PC matched the one listed in the "sh span" command. It was the root bridge. I decided to Google it and another person had posted about the same thing: A Windows 7 PC sending out BPDUs after bridging its interfaces. It appears, Windows 7 supports Spanning-Tree and in fact even been elected ROOT BRIDGE [M$ appears to use the same default priority as Cisco, so MAC Address was the tie breaker - The PC's was lower], which makes sense as bridging interfaces introduces the possibility of creating a switching loop.
R&S: CCENT → CCNA → CCNP → CCIE [ ]
Security: CCNA [ ]
Virtualization: VCA-DCV [ ]
Security: CCNA [ ]
Virtualization: VCA-DCV [ ]