IEEE 802.1D (referred as dot1d) and Cisco’s per VLAN Spanning Tree (PVST) BPDU encapsulations are supported on a per spoke SDP basis. STP is associated with a VPLS service like PVST is per VLAN. The main difference resides in the Ethernet and LLC framing and a type-length-value (TLV) field trailing the BPDU.
Table: Spoke SDP BPDU encapsulation states shows differences between dot1D and PVST Ethernet BPDU encapsulations based on the interface encap-type field.
| Field | dot1d encap-type null |
dot1d encap-type dot1q |
PVST encap-type null |
PVST encap-type dot1q |
|---|---|---|---|---|
Destination MAC |
01:80:c2:00:00:00 |
01:80:c2:00:00:00 |
N/A |
01:00:0c:cc:cc:cd |
Source MAC |
Sending Port MAC |
Sending Port MAC |
N/A |
Sending Port MAC |
EtherType |
N/A |
0x81 00 |
N/A |
0x81 00 |
Dot1p and DEI |
N/A |
0xe |
N/A |
0xe |
Dot1q |
N/A |
VPLS spoke-SDP ID |
N/A |
VPLS spoke-SDP encap value |
Length |
LLC Length |
LLC Length |
N/A |
LLC Length |
LLC DSAP SSAP |
0x4242 |
0x4242 |
N/A |
0xaaaa (SNAP) |
LLC CNTL |
0x03 |
0x03 |
N/A |
0x03 |
SNAP OUI |
N/A |
N/A |
N/A |
00 00 0c (Cisco OUI) |
SNAP PID |
N/A |
N/A |
N/A |
01 0b |
CONFIG or TCN BPDU |
Standard 802.1d |
Standard 802.1d |
N/A |
Standard 802.1d |
TLV: Type and Len |
N/A |
N/A |
N/A |
58 00 00 00 02 |
TLV: VLAN |
N/A |
N/A |
N/A |
VPLS spoke-SDP encap value |
Padding |
As Required |
As Required |
N/A |
As Required |
Each spoke SDP has a Read Only operational state that shows which BPDU encapsulation is currently active on the spoke SDP. The following states apply:
dot1d
Specifies that the switch is currently sending IEEE 802.1D standard BPDUs. The BPDUs are tagged or non-tagged based on the encapsulation type of the egress interface and the encapsulation value defined in the spoke-SDP. A spoke SDP defined on an interface with encapsulation type dot1q continues in the dot1d BPDU encapsulation state until a PVST encapsulated BPDU is received, after which the spoke-SDP converts to the PVST encapsulation state. Each received BPDU must be properly IEEE 802.1q tagged if the interface encapsulation type is defined as dot1q.
PVST
Specifies that the switch is currently sending proprietary encapsulated BPDUs. PVST BPDUs are only supported on Ethernet interfaces with the encapsulation type set to dot1q. The spoke SDP continues in the PVST BPDU encapsulation state until a dot1d encapsulated BPDU is received, in which case the spoke SDP reverts to the dot1d encapsulation state. Each received BPDU must be properly IEEE 802.1q tagged with the encapsulation value defined for the spoke SDP.
Dot1d is the initial and only spoke-SDP BPDU encapsulation state for spoke SDPs defined on an Ethernet interface with encapsulation type set to null.
Each transition between encapsulation types optionally generates an alarm that can be logged and optionally transmitted as an SNMP trap.