Cisco Wide Area Application Engine 612 Manual de usuario descargar pdf (Pagina 21)

Interception Techniques and Protocols 95

Flow Protection

When a WAE (re)joins the service group, a new Redirect Assignment message is generated

by the lead WAE. When the new WAE begins receiving redirected trafﬁc from the routers

in the service group, it does one of two things, depending on whether or not the redirected

trafﬁc is for a new connection or part of an existing connection. Trafﬁc associated with

newly established connections is evaluated against the Application Trafﬁc Policy (ATP) and

processed normally by the WAE. Trafﬁc associated with existing connections is forwarded

directly to the WAE that previously owned the bucket for that connection. This WCCPv2

mechanism is called ﬂow protection and is enabled by default. Flow protection allows for

existing connections to continue to be optimized even when the trafﬁc assignments for the

WAEs in a service group change.

Graceful Shutdown

After the no wccp ver 2 command is issued, WCCPv2 checks whether any connections are

being served by the WAE. If zero connections are being served, the shutdown is immediately

carried out. If there are more than zero connections being served, WCCPv2 waits for the

user-conﬁgured wccp shutdown max-wait XX time.

During this time, if the connection count goes down to zero, shutdown is immediately done.

At the end of the max-wait time, if the connection count has decreased but is still non-zero,

the shutdown count waits another 60 seconds, in the hope that if the connection count has

decreased other connections may complete too. At the end of the max-wait time, if the

connection count has not decreased, shutdown is immediately done. During the 60-second

incremental wait, if the connection count becomes zero, shutdown is done. At the end of the

60-second incremental wait, if the connection count has not reduced, the shutdown is done.

At the end of the 60-second incremental wait, if the count has further reduced but is still

non-zero, another 60-second incremental wait is done.

Unless the user interrupts the wait period, the code waits ﬁrst for the conﬁgured length of

time. If it thinks that connections are reducing, it waits a little longer in the hope that more

connections can be completed. However, if it realizes that the connection count has not

decreased, it discontinues waiting and shuts down.

Scalability

With WCCPv2, each service group can support up to 32 routers and 32 WAEs. This means

that a single service group can support N × 32 concurrent optimized TCP connections,

where N is the number of concurrent optimized TCP connections supported by the largest

WAE model. Each WAE in the service group is manually conﬁgured with the IP address of

each router in the service group. The WAE then uses unicast packets to exchange WCCPv2

messages with each router. It is not required that the routers in the service are manually

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Cisco Wide Area Application Engine 612 Manual de usuario Pagina 21