Out-of-Path with WCCP Redundant (Active/Active) Appliances : Configuring Flow Redirection
Configuring Flow Redirection
Why would you do flow redirection with WCCP?
n
To provide Network Acceleration, Silver Peaks require symmetric TCP flows. A network is asymmetric when a client request and its server response don’t use the same path through the network.
n
Flow redirection removes asymmetry locally by merging the traffic of an asymmetric flow into a single appliance. When peer appliances are configured as a cluster, they keep track of which appliance first saw a flow and consequently “owns” that flow. If a return flow arrives at a peer that doesn’t own it, the flow is forwarded to the rightful owner via the mgmt1 interfaces.
Note IMPORTANT — When configuring for flow redirection, the mgmt1 interfaces need to be in a separate subnet from the mgmt0 interfaces.
n
An appliance that handles both directions of traffic for a flow can then optimize the flow properly. Specifically, this sets the stage for TCP acceleration and CIFS acceleration.
This sequence of four diagrams illustrates how the need for flow redirection arises, and is resolved.
At Site A, the router load balances outbound flows to A1 and A2 based on the WCCP weights assigned.
Appliance B advertises its reachability to Appliances A1 and A2.
At A1, the flow is placed in the tunnel to Site B.
Appliances A1 and A2 are advertising their subnet’s reachability to Appliance B. Because A1 and A2 are in the same subnet, they’re equally likely to receive the return flow.
Appliance B doesn’t know that the two Silver Peaks at Site A are doing WCCP or how the loads are being balanced.
•
If Appliance B places the flow in the tunnel to A1, the flow will be symmetric.
•
If Appliance B places the flow in the tunnel to A2, this might result in an asymmetric flow.
However, having been configured into a flow redirection cluster, the peers know that A1 owns the flow and forward it there.
A1 returns the flow to the server.
Since both directions traversed A1, the flow is symmetric and able to be TCP optimized.
w
To configure flow redirection on Appliance A1
1
From A1’s menu, select Configuration > Interfaces. The Configuration - Interfaces page appears.
2
Configure the IP address for mgmt1 on A1.
a
Change the default address to 10.10.10.1/30.
b
Change Admin to up.
c
Click Apply.
d
Save the changes.
3
Select Configuration > Flow Redirection. The Flow Redirection page appears.
a
Select Enable.
b
In the Interface field, select mgmt1.
c
Click Add Peer, and enter the IP address of mgmt1 on A2. In this example, it’s 10.10.10.2.
d
Click Apply.
e
Save the changes.
w
To configure flow redirection on Appliance A2
1
From A2’s menu, select Configuration > Interfaces. The Configuration - Interfaces page appears.
2
Configure the IP address for mgmt1 on A2.
a
Change the default address to 10.10.10.2/30.
b
Change Admin to up.
c
Click Apply.
d
Save the changes.
3
Select Configuration > Flow Redirection. The Flow Redirection page appears.
a
Select Enable.
b
In the Interface field, select mgmt1.
c
Click Add Peer, and configure the IP address of mgmt1 on A1. In this example, it’s 10.10.10.1.
d
Click Apply.
e
Save the changes.
4
To verify that flow redirection is working, look to see that the State changes to OK, indicating that the interfaces and flow redirection are configured properly on both sides.
Please send comments or suggestions regarding user documentation to techpubs@silver-peak.com.