Cisco Wide Area Application Engine 612 Instrukcja Użytkownika Pobierz pdf (Strona 16)

90 Chapter 4: Network Integration and Interception

The command output shows that the only difference between services 61 and 62 is the value

from the packet used as the hash key. By default, service group 61 hashes on the source

IP address and service group 62 hashes on the destination IP address. Later, this chapter

discusses the signiﬁcance of the hash key used in each service group. By default, the spoof-

client-ip feature is enabled for both services. This is the WCCPv2 feature that allows WAAS

to handle optimized trafﬁc transparently. Trafﬁc forwarded to the WAE uses the same

source and destination IP addresses and TCP ports as when it entered the WAE.

The tcp-promiscuous services deﬁne TCP as the protocol and do not deﬁne any ports. By

not deﬁning any ports as part of the service groups, this causes interception and redirection

of all TCP trafﬁc. When trafﬁc passes through an interface in the IOS device with WCCPv2

redirection conﬁgured, it is evaluated against the protocol and port combination deﬁned by

the service to determine whether or not the packet should be redirected. By default this is

the only criteria that is used to determine whether or not a packet is redirected. It is important

to note that the IOS WCCPv2 implementation is not stateful. This means that IOS WCCPv2

is only dealing with redirected trafﬁc on a packet-by-packet basis. It does not keep track of

TCP connection state for redirected trafﬁc. On the other hand, the WCCPv2 implementation

in WAAS is stateful. WAAS tracks each connection as a ﬂow throughout the life of the

connection.

Forwarding and Return Methods

WCCPv2 supports different methods for forwarding redirected trafﬁc to a WAE, and for the

WAE to return trafﬁc to the router for forwarding. These methods are referred to as the

forwarding and return methods and are negotiated between IOS and the WAE when a WAE

joins the service group.

The forwarding method deﬁnes how trafﬁc that is being redirected from IOS to the WAE is

transmitted across the network. The ﬁrst method, GRE forwarding, encapsulates the original

packet in an IP GRE header with the destination IP address set to the target WAE and the

source IP address set to the WCCPv2 router ID of the redirecting router. When the WAE

receives the GRE-encapsulated packet, the GRE header is removed, and the packet is

processed. Figure 4-6 shows an example of GRE forwarding.

The second forwarding method, L2 forwarding, simply rewrites the destination MAC

address of the packet being redirected to equal the MAC address of the target WAE. This

forwarding method assumes that the WAE is Layer 2 adjacent to the redirecting router. L2

forwarding was originally developed for the WCCPv2 implementation on hardware-based

platforms, such as the Catalyst 6500. Figure 4-7 shows an example of L2 forwarding.

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Cisco Wide Area Application Engine 612 Instrukcja Użytkownika Strona 16