HP StorageWorks Enterprise File Services WAN Accelerator 3.0.4 deployment guide (AG421-96001, March 2007)

46 5 - CONNECTION FORWARDING
If you have one path (through HP EFS WAN Accelerator-2) from the client to the
server and a different path (through HP EFS WAN Accelerator-3) from the server to
the client, you need to enable in-path connection forwarding and configure the HP EFS
WAN Accelerators to communicate with each other. These HP EFS WAN Accelerators
are called neighbors and exchange connection information to redirect packets to each
other.
Figure 5-1. Connection Forwarding in a Server-Side Asymmetric Network
For example, in Figure 5-1, packets from the client to the server go through HP EFS
WAN Accelerator-2 while packets from the server to the client go through HP EFS
WAN Accelerator-3. The connection is intercepted by HP EFS WAN Accelerator-1
and HP EFS WAN Accelerator-2 because the first Transmission Control Protocol
(TCP) packet went through HP EFS WAN Accelerator-2.
Because HP EFS WAN Accelerator-3 sees the packets but HP EFS WAN Accelerator-
2 has the relevant information to optimize them, HP EFS WAN Accelerator-3 redirects
the packets from the Server to the Client back to HP EFS WAN Accelerator-2 so that
the connection can be intercepted and optimized correctly by HP EFS WAN
Accelerator-2.
Neighbors in
Connection
Forwarding
You can configure multiple neighbors for an HP EFS WAN Accelerator. Neighbors
can be placed in the same physical site or in different sites, but the latency between
them should be small because the packets traveling between them are not optimized.
TIP: If the neighbors are placed on the same physical site, consider installing and configuring
an HP EFS WAN Accelerator with multiple pairs of ports (for example, Four-Port Copper
Gigabit-Ethernet Bypass) and connecting the multiple links to intercept all packets coming back
from the server without performing connection forwarding.
Load-Balancing Connection forwarding can also be used in networks where there is packet load-
balancing.
If there are more than two possible paths, additional HP EFS WAN Accelerators must
be installed on each path and configured as neighbors. Neighbors receive information
in parallel (the delay introduced at connection set up is equal to the time it takes to get
an acknowledgement from the furthest neighbor).