Citrix NetScaler EE, Installation And Configuration Manual

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WCCP Mode
Sep 11, 2014
Web Cache Communication Protocol (WCCP) is a dynamic routing protocol introduced by Cisco. Originally intended only for
web caching, WCCP version 2 became a more general-purpose protocol, suitable for use by accelerators such as Citrix
NetScaler SD-WAN appliances.
WCCP mode is the simplest way of installing a SD-WAN appliance when inline operation is impractical. It is also useful where
asymmetric routing occurs, that is, when packets from the same connection arrive over different WAN links. In WCCP mode,
the routers use the WCCP 2.0 protocol to divert traffic through the appliance. Once received by the appliance, the traffic is
treated by the acceleration engine and traffic shaper as if it were received in inline mode.
Note:
For the purposes of this discussion, WCCP version 1 is considered obsolete and only WCCP version 2 is presented.
The standard WCCP documentation calls WCCP clients “caches.” To avoid confusion with actual caches, Citrix generally
avoids calling a WCCP client a “cache.” Instead, WCCP clients are typically called “appliances.”
This discussion uses the term “router” to indicate WCCP-capable routers and WCCP-capable switches. Though the term
“router” is used here, some high-end switches also support WCCP, and can be used with SD-WAN appliances.
The SD-WAN appliances support two WCCP modes:
WCCP is the original SD-WAN WCCP offering supported since release 3.x. It supports a single appliance service group (no
clustering).
WCCP clustering, introduced in release 7.2, allows your router to load-balance traffic between multiple appliances.
The physical mode for WCCP deployment of a SD-WAN appliance is one-arm mode in which the appliance is connected
directly to a dedicated port on the WAN router. The WCCP standard includes a protocol negotiation in which the appliance
registers itself with the router, and the two negotiate the use of features they support in common. Once this negotiation
is successful, traffic is routed between the router and the appliance according to the WCCP router and redirection rules
defined on the router.
A WCCP-mode appliance requires only a single Ethernet port. The appliance should either be deployed on a dedicated
router port (or WCCP-capable switch port) or isolated from other traffic through a VLAN. Do not mix inline and WCCP
modes.
The following figure shows how a router is configured to intercept traffic on selected interfaces and forward it to the
WCCP-enabled appliance. Whenever the WCCP-enabled appliance is not available, the traffic is not intercepted, and is
forwarded normally.
Figure 1. WCCP Traffic Flow
WCCP allows traffic to be forwarded between the router and the appliance in either of the following modes:
L2 Mode— Requires that the router and appliance be on the same L2 segment (typically an Ethernet segment). The IP
packet is unmodified, and only the L2 addressing is altered to forward the packet. In many devices, L2 forwarding is