Srrp And Multi-Chassis Synchronization - Alcatel-Lucent 7750 SR OS Service Manual

timer is not utilized when waiting to enter the master state. Also, SRRP always preempts when the
local priority is better than the current master and the backup SRRP instance always inherits the
master's advertisement interval from the SRRP advertisement messaging.
SRRP advertisement messages carry a becoming-master indicator flag. The becoming-master flag
is set by a node that is attempting to usurp the master state from an existing SRRP master router.
When receiving an SRRP advertisement message with a better priority and with the becoming-
master flag set, the local master initiates its becoming-backup state, stops routing with the SRRP
gateway MAC and sends an SRRP advertisement message with a priority set to zero. The new
master continues to send SRRP advertisement messages with the becoming-master flag set until it
either receives a return priority zero SRRP advertisement message from the previous master or its
becoming-master state timer expires. The new backup node continues to send zero priority SRRP
advertisement messages every time it receives an SRRP advertisement message with the
becoming-master flag set. After the new master either receives the old masters priority zero SRRP
advertisement message or the become-master state timer expires, it enters the master state. The
become-master state timer is set to 10 seconds upon entering the become-master state.
The SRRP advertisement message is always evaluated to see if it has higher priority than the
SRRP advertisement that would be sent by the local node. If the advertised priority is equal to the
current local priority, the source IP address of the received SRRP advertisement is used as a tie
breaker. The node with the lowest IP address is considered to have the highest priority.
The SRRP instance maintains the source IP address of the current master. If an advertisement is
received with the current masters source IP address and the local priority is higher priority than the
masters advertised priority, the local node immediately enters the becoming-master state unless
the advertised priority is zero. If the advertised priority is zero, the local node bypasses the
becoming-master state and immediately enters the master state. Priority zero is a special case and
is sent when an SRRP instance is relinquishing the master state.

SRRP and Multi-Chassis Synchronization

In order to take full advantage of SRRP resiliency and diagnostic capabilities, the SRRP instance
should be tied to a MCS peering that terminates on the redundant node. The SRRP instance is tied
to the peering using the srrp srrp-id command within the appropriate MCS peering configuration.
Once the peering is associated with the SRRP instance, MCS will synchronize the local
information about the SRRP instance with the neighbor router. MCS automatically derives the
MCS key for the SRRP instance based on the SRRP instance ID. For example, an SRRP instance
ID of 1 would appear in the MCS peering database with a MCS-key srrp-0000000001.
The SRRP instance information stored and sent to the neighbor router consists of:
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7750 SR OS Services Guide
The SRRP instance MCS key
Containing service type and ID
Containing subscriber IP interface name
Subscriber subnet information
Internet Enhanced Services
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