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Configuring Interface and Router Redundancy

2-2 114079 Rev. A

Redundancy Protocol

Routers in a redundancy group all begin in the secondary role.

A router assumes the primary role according to the following criteria, and the

redundancy protocol considers the criteria in the following order. For example, if

two routers in a router redundancy group have the same number of good

interfaces, the protocol considers the number of reachable resources each router

has. But if one router has a larger number of good interfaces, that router becomes

primary without consideration of subsequent criteria.

1. Number of good interfaces

2. Number of reachable resources

3. Priority to become primary, which you conﬁgure

4. Lowest member ID (for further information, see the Member ID parameter in

Chapter 5)

The routers 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).

Table 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.

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Avaya Configuring Interface and Router Redundancy Manuel d'utilisateur Page 28

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