Ip forwarding cache – Brocade TurboIron 24X Series Configuration Guide User Manual
Page 472
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Brocade TurboIron 24X Series Configuration Guide
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Overview
NOTE
Layer 2 Switches do not have an IP route table. A Layer 2 Switch sends all packets addressed to
another subnet to the default gateway, which you specify when you configure the basic IP
information on the Layer 2 Switch.
The IP route table can receive the paths from the following sources:
•
A directly-connected destination, which means there are no router hops to the destination
•
A static IP route, which is a user-configured route
•
A route learned through RIP
•
A route learned through OSPF
•
A route learned through BGP4
The IP route table contains the best path to a destination:
•
When the software receives paths from more than one of the sources listed above, the
software compares the administrative distance of each path and selects the path with the
lowest administrative distance. The administrative distance is a protocol-independent value
from 1 – 255.
•
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.
Each IP route table entry contains the destination IP address and subnet 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 IP metric (cost), and the type. The type
indicates how the IP route table received the route.
To display the IP route table, refer to
“Displaying the IP route table”
on page 501 (Layer 3 Switch
only)
To configure a static IP route, refer to
on page 465 (Layer 3 Switch only)
To clear a route from the IP route table, refer to
on page 503 (Layer 3 Switch
only)
To increase the size of the IP route table for learned and static routes, refer to the section
“Displaying and modifying system parameter default settings”
•
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 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 destination:
Destination NetMask Gateway Port Cost Type
10.1.0.0 255.255.0.0
10.1.1.2 1
2 R