Cisco Wide Area Application Engine 612 Manual de usuario descargar pdf (Pagina 20)

94 Chapter 4: Network Integration and Interception

Failure Detection

Once a WAE has successfully joined a service group, a periodic keepalive packet is sent

every 10 seconds from the WAE to each router in the service group. The keepalive mechanism

occurs independently for each conﬁgured service group. If a router in the service group has

not received a keepalive packet from the WAE in 25 seconds, the router unicasts a Removal

Query message to that WAE requesting that it immediately respond. If no response is received

within 5 seconds, for a total of 30 seconds since the last keepalive message from the WAE,

the WAE is considered ofﬂine and is removed from the service group. Figure 4-10 illustrates

this behavior.

Figure 4-10 WCCP Keepalive Timeout

When the WAE is removed from the service group, it is reﬂected in the Router View

advertised from each router in the service group. When the lead WAE determines that a

WAE has been removed from the service group, it generates a Redirect Assignment message

to each router in the service group. The Redirect Assignment message instructs the routers

how to reallocate the buckets across the remaining WAEs in the service group. The length

of time required to calculate the new assignments might very depending upon when the

group of WAEs becomes stable. The WAE waits a minimum of 9 seconds. The maximum

length of time depends on when the IOS device sends an update message without any

changes indicated, typically between 19 and 39 seconds.

WAE fails to send keepalive

within 25 seconds.

Router queries WAE directly.

WAE fails to respond to RQ within 5 seconds.

WAE removed from service group.

25s

WCCP Router WAE

ISU Response

Removal Query (RQ)

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Cisco Wide Area Application Engine 612 Manual de usuario Pagina 20