Hitachi US7070447-001 Route Cache Forwarding vs. IP Forwarding, Static Routes vs. Dynamic Routes

Draft Level—Hitachi Confidential

Troubleshooting at the Network Layer

To prevent routing loops, the HiSpeed switch implements Split Horizon.

Networks that are learned through a particular interface will not get advertised back out that same interface.

Note: RIP version 1 does not propagate subnets. RIP assumes that the same subnet mask is used throughout the entire network, therefore, ensure subnet masks are identical.

Route Cache Forwarding vs. IP Forwarding

The HiSpeed switch provides a fast data path for forwarding IP packets called Route Cache Forwarding. Only TCP/UDP traffic over IP is supported. To forward packets at a higher speed, a cache is maintained to store IP addresses and Layer 2 information. An entry is created for each communicating pair of IP addresses. Once a route is learned, traffic destined for the port will be forwarded directly to the interface without going through the IP Forwarding mechanism.

Tip: The Route Cache table can store up to 1024 routes and has an aging timer of five minutes. Currently, there is no mechanism for invalidating routes if there is an address or port change. Traffic will still be forwarded to the previous port. To continue to use the Route Cache feature, you must wait for the old entry to age out.

Static Routes vs. Dynamic Routes

Static routes are manually configured while dynamic routes are learned. Unlike dynamic routes, static routes never age out. To remove a static route, it must be manually deleted from the routing table.

Default Route

An address of 0.0.0.0 signifies a default route used for all unknown networks. Typically, the default route points to a router which maintains a complete routing table. A default route is commonly used on a router as an entry point to the Internet. Defining a default route on the HiSpeed switch allows the switch to forward packets to unknown destination networks via an external router.

US7070447-001, Rev 01 10-3