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Configuring Interface and Router Redundancy

2-2

Redundancy Protocol

Routers in a redundancy group all begin in the secondary role. They use a bidding

process to determine which router becomes the primary router. If the group has

more than two members, the bidding process also determines which of the backup

routers is the best secondary router. The bidding process consists of an exchange

of messages called

protocol data units

(PDUs).

able 2-1 provides a detailed description of this process.

Table 2-1. Redundancy Protocol PDU Flow Diagram for Role Bidding

Router A PDU Router B

Starts in secondary role. Starts in secondary role.

Sends Hello PDUs at periodic intervals.

These PDUs start the bidding for the

primary role.

Hello PDU

Role = Secondary

---------------->

Receives Hello PDU from Router A and

stores its contents in the redundancy

group database.

Checks to see if Router A is a better

primary router; if so, Router B does not

plan to change roles.

Receives Hello PDU from Router B and

stores its contents in the redundancy

group database.

Checks to see if Router B is a better

primary router; if so, Router A does not

plan to change roles.

Hello PDU

Role = Secondary

<----------------

Starts sending Hello PDUs at periodic

intervals; these PDUs are Router B’s

bids for the primary role.

After the bidding period times out, it is

determined that Router A is the best

primary router. Router A sends out the

SOS New Primary PDU, then performs

the role-changing action to become the

primary router.

SOS New Primary

PDU

Role = Secondary

---------------->

After the bidding period times out, it is

determined that another member of the

router redundancy group is the best

primary router. Router B remains in a

secondary role and continues to monitor

the redundancy group status.

Receives the periodic Hello PDU and

updates the redundancy group

database, including each member’s

interface status information.

Hello PDU

Role = Secondary

<----------------

Continues sending periodic Hello PDUs

with local interface status information.

(continued)

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Avaya Configuring Interface and Router Redundancy Manuel d'utilisateur Page 24

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