Virtual Private LAN Services
7750 SR OS Services Guide Page 443
BPDU Translation
VPLS networks are typically used to interconnect different customer sites using different access
technologies such as Ethernet and bridged-encapsulated ATM PVCs. Typically, different Layer 2
devices can support different types of STP and even if they are from the same vendor. In some
cases, it is necessary to provide BPDU translation in order to provide an interoperable e2e
solution.
To address these network designs, BPDU format translation is supported on 7750 SR devices. If
enabled on a given SAP or spoke SDP, the system will intercept all BPDUs destined to that
interface and perform required format translation such as STP-to-PVST or vice versa.
Similarly, BPDU interception and redirection to the CPM is performed only at ingress meaning
that as soon as at least 1 port within a given VPLS service has BPDU translation enabled, all
BPDUs received on any of the VPLS ports will be redirected to the CPM.
BPDU translation involves all encapsulation actions that the data path would perform for a given
outgoing port (such as adding VLAN tags depending on the outer SAP and the SDP encapsulation
type) and adding or removing all the required VLAN information in a BPDU payload.
This feature can be enabled on a SAP only if STP is disabled in the context of the given VPLS
service.
L2PT and BPDU Translation
Cisco Discovery Protocol (CDP), Digital Trunking Protocol (DTP), Port Aggregation Protocol
(PAGP), Uni-directional Link Detection (ULD) and Virtual Trunk Protocol (VTP) are supported.
These protocols automatically pass the other protocols tunneled by L2PT towards the CPM and all
carry the same specific Cisco MAC.
The existing L2PT limitations apply.
• The protocols apply only to VPLS.
• The protocols are mutually exclusive with running STP on the same VPLS as soon as one
SAP has L2PT enabled.
• Forwarding occurs on the CPM.
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