Troubleshooting guide
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Cisco Wide Area Application Services Configuration Guide
OL-26579-01
Chapter 1 Configuring Traffic Interception
Configuring WCCP on WAEs
(DRE) compression performance. Also, mask assignment on the Catalyst 6500 series switches uses the
ACL TCAM. When combined with WCCP redirect lists, mask assignment can use a large portion of the
TCAM. To minimize TCAM usage, use a mask with fewer care bits.
Given these considerations, beginning with WAAS version 4.2.1, the default mask has been changed
from src-ip-mask 0x1741 and dst-ip-mask 0x0 (in 4.1x versions) to src-ip-mask 0xF00 and
dst-ip-mask 0x0 (in 4.2.1 and later versions). The current source IP mask uses only 4 care bits rather than
the 6 care bits used by the old mask.
With a typical data center WCCP interception configuration (ingress interception with service 61 on the
WAN, ingress interception with service 62 on the LAN), this mask load balances /24 branch subnets (it
extracts the last 4 bits of /24 subnets). Connections from one branch subnet will be pinned to one data
center WAE. If your network has a different distribution of IP addresses (for example, /16 subnets), you
should configure a mask that extracts bits from the /16 network part of the address, for example,
src-ip-mask 0xF0000. Similarly, if some branches generate more traffic than others, you may want to
create a mask that also extracts bits from the host part of the address, for example, 0xF03.
Information About Packet-Forwarding Methods
A WCCP-enabled router redirects intercepted TCP segments to a WAE using one of the following two
packet-forwarding methods:
• Generic routing encapsulation (GRE)—Allows packets to reach the WAE even if there are any
number of routers in the path to the WAE.
• Layer 2 redirection—Allows packets to be switched at Layer 2 (MAC layer) and reach the WAE.
Table 1-2 describes the packet-forwarding methods.
The redirection mode is controlled by the branch WAE. The first branch WAE that joins the WCCP
service group decides the forwarding method (GRE or Layer 2 redirection) and the assignment method
(hashing or masking). The term mask assignment refers to WCCP Layer 2 Policy Feature Card 2 (PFC2)
input redirection.
If masking is selected with WCCP output redirection, then the branch WAE falls back to the original
hardware acceleration that is used with the Multilayer Switch Feature Card (MSFC) and the Policy
Feature Card (PFC).
Table 1-2 Packet-Forwarding Methods
Packet-Forwarding
Method
Load-Balancing Method:
Hashing
Load-Balancing Method:
Masking
GRE (Layer 3) Packet redirection is completely
handled by the router software.
Packet redirection is handled by the router
software. We do not recommend using mask
assignment when GRE is being used as the
packet-forwarding method.
Layer 2 redirection First redirected packet is handled
by the router software; all
subsequent redirected packets are
handled by the router hardware.
All packets are handled by the router
hardware (currently supported only on the
Catalyst 6500 series switches or Cisco 7600
series routers because special hardware is
required).