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

54 6 - POLICY-BASED ROUTING DEPLOYMENTS
PBR checks availability in the following manner:
1. When PBR first attempts to send to a PBR next hop, it checks the CDP neighbor
table to see if the IP address of the next hop appears to be available. If so, it sends
an Address Resolution Protocol (ARP) request for the address, resolves it, and
begins redirecting traffic to the next hop (that is, the HP EFS WAN Accelerator).
2. After PBR has verified the next hop, it continues to send to the next hop as long as
it obtains answers from the ARP request for the next hop IP address. If the ARP
request fails to obtain an answer, it then rechecks the CDP table. If there is no entry
in the CDP table, it no longer uses the route map to send traffic. This verification
provides a failover mechanism.
NOTE: Using PBR with CDP will not work on a Cisco 6500 router and switch combination
that is setup in hybrid mode. You must use a native setup for this to work. A hybrid setup fails
because all the routing is done on the Multilayer Switch Feature Card (MSFC). This card is
treated as an independent system in a hybrid setup. Therefore, when you run the show cdp
neighbors command on the MSFC, it displays the Supervisor card as its only neighbor. It does
not see any of the devices that are connected to the switch ports. Therefore, it assumes none of
those devices are reachable, and it does not redirect any traffic for route maps that use set ip
next-hop verify-availability.
In more recent versions of the Cisco IOS software, there is a feature called PBR with
Multiple Tracking Options. In addition to the old method of using CDP information, it
allows methods such as HTTP and ping to be used to determine whether the PBR next
hop is available. Using CDP allows you to run with older IOS 12.x versions.
NOTE: CDP is required for failover deployments on Cisco 6000, 6500, and 7600 platforms
because Multiple Tracking Options is not available on these platforms.
For an example configuration, see “Symmetric Deployments with PBR,
Auto-Discovery, and CDP” on page 66.
Connecting the HP EFS WAN
Accelerator to Your Network in PBR
Deployments
There are two Ethernet cables attached to the HP EFS WAN Accelerator in PBR
deployments:
 A straight-through cable to the Primary interface. You use this connection to
manage the HP EFS WAN Accelerator, reaching it through HTTPS or SSH.
 A straight-through cable to the WA N interface. You assign an IP address to the in-
path interface; this is the IP address that you redirect traffic to (that is, the target
of the router PBR rule).