Foundry Networks Switch and Router Installation And Configuration Manual page 448

Foundry Switch and Router Installation and Configuration Guide
• When the software receives two or more best paths from the same source and the paths have the same
metric (cost), the software can load share traffic among the paths based on destination host or network
address (based on the configuration and the Layer 3 Switch model).
Here is an example of an entry in the IP route table:
Destination
1.1.0.0
Each IP route table entry contains the destination's IP address and sub-net mask and the IP address of the next-
hop router interface to the destination. Each entry also indicates the port attached to the destination or the next-
hop to the destination, the route's IP metric (cost), and the type. The type indicates how the IP route table
received the route.
To display the IP route table, see the following:
• "Displaying the IP Route Table" on page 15-94 – Layer 3 Switch only
To configure a static IP route, see the following:
• "Configuring Static Routes" on page 15-39 – Layer 3 Switch only
To clear a route from the IP route table, see the following:
• "Clearing IP Routes" on page 15-97 – Layer 3 Switch only
To increase the size of the IP route table for learned and static routes, see "Displaying and Modifying System
Parameter Default Settings" on page 10-70:
• For learned routes, modify the ip-route parameter.
• For static routes, modify the ip-static-route parameter.
IP Forwarding Cache
The IP forwarding cache provides a fast-path mechanism for forwarding IP packets. The cache contains entries
for IP destinations. When a Foundry Layer 3 Switch has completed processing and addressing for a packet and is
ready to forward the packet, the device checks the IP forwarding cache for an entry to the packet's destination.
• If the cache contains an entry with the destination IP address, the device uses the information in the entry to
forward the packet out the ports listed in the entry. The destination IP address is the address of the packet's
final destination. The port numbers are the ports through which the destination can be reached.
• If the cache does not contain an entry and the traffic does not qualify for an entry in the session table instead,
the software can create an entry in the forwarding cache.
Each entry in the IP forwarding cache has an age timer. If the entry remains unused for ten minutes, the software
removes the entry. The age timer is not configurable.
NOTE: The forwarding cache on Foundry Layer 2 Switches is used only for IP router acceleration (Layer 3
switching). See "Enabling IP or IPX Router Acceleration" on page 10-69.
Here is an example of an entry in the IP forwarding cache:
IP Address
1 192.168.1.11
Each IP forwarding cache entry contains the IP address of the destination, and the IP address and MAC address
of the next-hop router interface to the destination. If the destination is actually an interface configured on the
Layer 3 Switch itself, as shown here, then next-hop information indicates this. The port through which the
destination is reached is also listed, as well as the VLAN and Layer 4 QoS priority associated with the destination
if applicable.
To display the IP forwarding cache, see "Displaying the Forwarding Cache" on page 15-92.
15 - 6
NetMask Gateway
255.255.0.0 99.1.1.2
Next Hop
DIRECT
Port
1/1
MAC Type
0000.0000.0000 PU
Cost Type
2 R
Port Vlan Pri
n/a 0
December 2000