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2.5  Ownership

We have already described different aspects of the mechanism VRRP defines for protecting interfaces, enabling a router to act as a default first hop router. In all the configurations we have discussed so far, the IP address protected by the virtual router was the real IP address of one of the participant VRRP routers. Take the configuration depicted in Figure 2-6. In this configuration the IP address protected by the virtual router V1 is the IP address of the router R1. We refer to such routers, the real IP address(es) of which is associated with the virtual router, as owner. In Figure 2-6, by definition, R1 is not only the master but also an owner. For example, in Figure 2-6, the IP address IP(V1) protected by virtual router V1 is also a real IP address IP(R1) of the VRRP router R1. For that reason, R1 qualifies as the owner of the virtual router V1.

Ownership leads to some special characteristics in a VRRP router. VRRP requires the owner to assume the priority 255 and to become the master at the initialization. Another characteristic is related to the situation in which a failed master becomes operational again. In such cases the owner becomes unconditionally master again. By the same token, as long as it is operational, an owner remains master independent of the status of the other VRRP routers.

The situation is a little bit more complex when neither the current master nor the router that is in the process of becoming operational is an owner. In that case the result depends on the priorities of the routers as well as on the value of a flag called preemption mode. The preemption flag regulates whether a new operational nonowner can displace the current master based on its priority.

For the sake of brevity, let us call a master becoming operational after a failure a new contestant and use the term incumbent for the current master from the perspective of its bid for a new election. As indicated above, since the mastership of an owner is unconditional, a new contestant cannot displace an incumbent owner. By the same token, a new contestant that is also an owner always displaces the incumbent.

But if the incumbent and the new contestant are not owners, in such cases the decision depends on the priorities and the preemption mode. If the priority of the incumbent is higher than that of the new contestant, the incumbent stays in its office. But if the priority of the new contestant is higher than that of the incumbent and if the preemption mode is set to true, the new contestant becomes the master. On the other hand, if the preemption mode is defined as false, in such cases the incumbent keeps its office even if it were to have lower priority. Table 2-2 summarizes the logical structure of this decision flow.

TABLE 2-2.  Impact of Ownership in a New Election

INCUMBENT

NEW CONTESTANT

PREEMPTION MODE

RESULT

Owner

Not an owner

False

No change

Owner

Not an owner

True

No change

Not an owner

Owner

False

Change

Not an owner

Owner

True

Change

Not an owner

Not an owner

False

No change

Not an owner

Not an owner

True

Requires election


From Table 2-2, you can deduce that there can be at most one master in a given virtual router. For that reason, you do not see any row in which both the incumbent and the new contestant are owners. Note that we did not discuss above the equality cases for priorities. This subject is covered extensively in Chapter 4.

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