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
The default egress method is L2. This egress method sends optimized data out through a Layer 2
connection to the router. This method is available only if the redirect method is also set to WCCP L2,
and is not available on devices using WAAS versions earlier than 5.0. The router must also support Layer
2 redirect. If you configure the WCCP GRE redirect method or switch between WCCP GRE and L2, the
default egress method is set to IP Forwarding.
For devices with a WAAS version earlier than 5.0, the default egress method is IP forwarding. The IP
forwarding egress method does not allow you to place WAEs on the same VLAN or subnet as the clients
and servers, and it does not ensure that packets are returned to the intercepting router.
The WCCP GRE return and generic GRE egress methods allow you to place WAEs on the same VLAN
or subnet as clients and servers. Repeating redirection is prevented by encapsulating the outgoing frames
in the GRE frames. Cisco IOS routers handle these GRE frames as bypass frames and do not apply
WCCP redirection. With the WCCP GRE return method, WAAS uses the router ID address as the
destination for GRE frames; with the generic GRE method, WAAS uses the address of the router
configured in the WAE router list.
This technique makes it possible to support redundant routers and router load balancing; WAAS makes
a best effort to return frames back to the router from which they arrived, though this is not guaranteed.
An exception is that if flow protection is enabled, the WAE is unable to return flow-protected traffic to
the originating router because the router information is not available.
Note Network designs that require redirected frames to be returned to the originating router are not compatible
with the WCCP flow-protection feature.
If you want to use this functionality with multiple routers connected to the WAAS network segment, you
must ensure connectivity to the router ID address, for example, by configuring static routes. The router
ID is the address of the first loopback interface or highest active physical interface. This address can be
found in the output of the show wccp routers EXEC command.
WAAS applies the following logic in its router selection for WCCP GRE and generic GRE:
• When the WAAS software applies data redundancy elimination (DRE) and compression to a TCP
flow, the number of packets that are sent out may be fewer. A single packet that carries optimized
data may represent original data that was received in multiple packets redirected from different
routers. That optimized data-carrying packet will egress from the WAE to the router that last
redirected a packet to the WAE for that flow direction.
• When the WAE receives optimized data, the data may arrive in multiple packets from different
routers. The WAAS software expands the optimized data back to the original data, which will be
sent out as several packets. Those original data-carrying packets will egress from the WAE to the
router that last redirected a packet to the WAE for that flow direction.
The WCCP GRE return and generic GRE egress methods are similar, but the generic GRE egress method
is designed specifically to be used in deployments where the router or switch does hardware-accelerated
processing of GRE packets, such as with the Cisco 7600 series router or the Catalyst 6500 series switch
with the Supervisor Engine 32 or 720. Additionally, the generic GRE egress method returns packets to
the intercepting router by using a GRE tunnel that you must configure on the router (the WAE end of the
tunnel is configured automatically). The generic GRE egress method is supported only when the WCCP
GRE interception method is used.
To use the generic GRE egress method, you must create an intercepting router list on the WAE (multicast
addresses are not supported) and configure a GRE tunnel interface on each router. For details on
configuring GRE tunnel interfaces on the routers, see the “Configuring a GRE Tunnel Interface on a
Router” section on page 1-31.