Virtual Private LAN Services
7750 SR OS Services Guide Page 533
Operationally Forwarding
Configuration BPDUs are sent out a SAP in the forwarding state. Layer 2 frames received on the
SAP are source learned and destination forwarded according to the FIB. Layer 2 frames received
on other forwarding interfaces and destined for the SAP are also forwarded.
SAP BPDU Encapsulation State
IEEE 802.1d (referred as Dot1d) and Cisco’s per VLAN Spanning Tree (PVST) BPDU
encapsulations are supported on a per SAP basis. STP is associated with a VPLS service like
PVST is associated per VLAN. The main difference resides in the Ethernet and LLC framing and
a type-length-value (TLV) field trailing the BPDU.
The following table shows differences between Dot1d and PVST Ethernet BPDU encapsulations
based on the interface encap-type field:
Table 13: SAP BPDU Encapsulation States
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 CFI N/A 0xe N/A 0xe
Dot1q N/A VPLS SAP ID N/A VPLS SAP 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 Standard 802.1d Standard 802.1d N/A Standard 802.1d
TLV: Type & Len N/A N/A N/A 58 00 00 00 02
TLV: VLAN N/A N/A N/A VPLS SAP encap value
Padding As Required As Required N/A As Required
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