Basic System Configuration Guide System Management
Edition: 01 3HE 11010 AAAC TQZZA 207
6.2.1.1.5 Multi-Chassis LAG Redundancy
Multi-chassis LAG (MC-LAG) prevents service interruptions that are caused by 7705
SAR nodes that are taken out of service for maintenance, upgrades, or relocation.
MC-LAG also provides redundancy for incidents of peer nodal failure. This improves
network resiliency. When typically used at access or aggregation sites, MC-LAG
ensures high availability without service disruptions by providing redundant access
or aggregation nodes.
MC-LAG extends the link level redundancy provided by LAG to include protection
against failure of a 7705 SAR node. With MC-LAG, a CE device can be connected
to two redundant-pair peer nodes. The redundant-pair peer nodes act like a single
node, using active/standby signaling to ensure that only one peer node is used at a
time. The redundant-pair peer nodes appear to be a single system as they share the
same MAC address and system priority when implementing MC-LAG. Availability
and status information are exchanged through an MC-LAG Control Protocol
(MCCP). It is used to ensure that one peer is active and to synchronize information
between the peers.
A peer is configured by specifying its IP address, to which the MCCP packets are
sent. The LAG ID, system priority, and MAC address for the MC-LAG are also
configured under the peer. Up to 16 MC-LAGs can be configured and they can either
use the same peer or different peers up to a maximum of 4 peers.
It is possible to specify the remote LAG ID in the MC-LAG lag command to allow the
local and remote LAG IDs to be different on the peers. If there are two existing nodes
which already have LAG IDs that do not match, and an MC-LAG is to be created
using these nodes, then the remote LAG ID must be specified so that the matching
MC-LAG group can be found. If no matching MC-LAG group can be found between
neighbor systems, the individual LAGs will operate as usual and no MC-LAG
operation is established.
Two timer options, keep-alive-interval and hold-on-neighbor-failure, are available
in the MC-LAG configuration. The keep-alive-interval option specifies the frequency
of the messages expected to be received from the remote peer and is used to
determine if the remote peer is still active. If hold-on-neighbor-failure messages
are missed, then it is assumed that the remote peer is down.
Figure 10 shows an example of MC-LAG deployed at access and aggregation sites.
Note: The 7705 SAR nodes must be of the same type, except for the 7705 SAR-8 and
7705 SAR-18, which can be used together in a redundant-pair configuration.
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