Virtual Private LAN Services
7210 SAS-X, R6 OS Services Guide Page 255
L2PT Termination
L2PT is used to transparently transport protocol data units (PDUs) of Layer 2 protocols such as
STP, CDP, DTP, VTP, PAGP, and UDLD. This allows running these protocols between customer
CPEs without involving backbone infrastructure.
The 7210 SAS routers allow transparent tunneling of PDUs across the VPLS core. However, in
some network designs, the VPLS PE is connected to CPEs through a legacy Layer 2 network,
rather than having direct connections. In such environments termination of tunnels through such
infrastructure is required.
L2PT tunnels protocol PDUs by overwriting MAC destination addresses at the ingress of the
tunnel to a proprietary MAC address such as 01-00-0c-cd-cd-d0. At the egress of the tunnel, this
MAC address is then overwritten back to MAC address of the respective Layer 2 protocol.
The 7210 SAS nodes support L2PT termination for STP BPDUs. More specifically:
• At ingress of every SAPwhich is configured as L2PT termination, all PDUs with a MAC
destination address, 01-00-0c-cd-cd-d0 will be intercepted and their MAC destination
address will be overwritten to MAC destination address used for the corresponding
protocol. The type of protocol can be derived from LLC and SNAP encapsulation.
• In egress direction, PDUs of the corresponding protocol received on all VPLS ports will
be intercepted and L2PT encapsulation will be performed for SAPs configured as L2PT
termination points. Because of the implementation reasons, PDU interception and re-
direction to CPM can be performed only at ingress. Therefore, to comply with the above
requirement, as soon as at least 1 port of a given VPLS service is configured as L2PT
termination port, redirection of PDUs to CPM will be set on all other ports (SAPs) of the
VPLS service.
L2PT termination can be enabled only if STP is disabled in a context of the given VPLS service.
To Next Page
Loading...
