Page 442 7750 SR OS Services Guide
L2PT Termination
L2PT is used to transparently transport protocol data units (PDUs) of Layer 2 protocols such as
STP, CDP, VTP and PAGP and UDLD. This allows running these protocols between customer
CPEs without involving backbone infrastructure.
7750 SR 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.
7750 SR routers support L2PT termination for STP BPDUs. More specifically:
• At ingress of every SAP/spoke SDP which 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 (PVST, STP, RSTP). The type of the STP protocol can be derived
from LLC and SNAP encapsulation.
• In egress direction, all STP PDUs received on all VPLS ports will be intercepted and
L2PT encapsulation will be performed for SAP/spoke SDPs 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, spoke
SDPs and mesh SDPs) 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...
