LAG
Page 70 7210 SAS M, T, X, R6, R12, Mxp Interface Configu-
ration Guide
Multi-Chassis LAG
This section describes the Multi-Chassis LAG (MC-LAG) concept. MC-LAG is an extension of a
LAG concept that provides node-level redundancy in addition to link-level redundancy provided
by “regular LAG”.
Note: This feature is supported only on 7210 SAS-R6, 7210 SAS-R12,7210 SAS-X, 7210 SAS-M,
7210 SAS-T, and 7210 SAS-Mxp network mode. It is not supported in 7210 SAS-T and 7210
SAS-M access-uplink mode.
Typically, MC-LAG is deployed in a network-wide scenario providing redundant connection
between different end points. The whole scenario is then built by combination of different
mechanisms (for example, MC-LAG and redundant pseudowire to provide e2e redundant p2p
connection or dual homing of DSLAMs in Layer 2/3 TPSDA).
NOTE: The 7210 SAS platforms configured in access-uplink mode cannot peer with an MC-
LAG-enabled node since it does not implement MC-LAG protocol. In other words, 7210 SAS-
M,T in access-uplink mode cannot provide MC-LAG server functionality. Instead they can be
used as MC-LAG clients, with the platforms connected to a head-end node that support MC-LAG
server functionality. These platforms connect to the head-end node using LAG.
Overview
Multi-chassis LAG is a method of providing redundant Layer 2/3 access connectivity that extends
beyond link level protection by allowing two systems to share a common LAG end point.
The multi-service access node (MSAN) node is connected with multiple links towards a redundant
pair of Layer 2/3 aggregation nodes such that both link and node level redundancy, are provided.
By using a multi-chassis LAG protocol, the paired Layer 2/3 aggregation nodes (referred to as
redundant-pair) appears to be a single node utilizing LACP towards the access node. The multi-
chassis LAG protocol between redundant-pair ensures a synchronized forwarding plane to/from
the access node and is used to synchronize the link state information between the redundant-pair
nodes such that proper LACP messaging is provided to the access node from both redundant-pair
nodes.
In order to ensure SLAs and deterministic forwarding characteristics between the access and the
redundant-pair node, the multi-chassis LAG function provides an active/standby operation
towards/from the access node. LACP is used to manage the available LAG links into active and
standby states such that only links from 1 aggregation node are active at a time to/from the access
node.
Characteristics related to MC are:
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