Configuration Guide User guide

FastIron Configuration Guide 953
53-1002494-02
IP configuration overview
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 Brocade 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:
• 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 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.
Here is an example of an entry in the IP forwarding cache.
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, refer to “Displaying the forwarding cache” on page 1073.
NOTE
You cannot add static entries to the IP forwarding cache, although you can increase the number of
entries the cache can contain. Refer to the section “Displaying and modifying system parameter
default settings” on page 578.
Layer 4 session table
The Layer 4 session provides a fast path for forwarding packets. A session is an entry that contains
complete Layer 3 and Layer 4 information for a flow of traffic. Layer 3 information includes the
source and destination IP addresses. Layer 4 information includes the source and destination TCP
and UDP ports. For comparison, the IP forwarding cache contains the Layer 3 destination address
but does not contain the other source and destination address information of a Layer 4 session
table entry.
The Layer 2 Switch or Layer 3 Switch selects the session table instead of the IP forwarding table for
fast-path forwarding for the following features:
• Layer 4 Quality-of-Service (QoS) policies
• IP access policies
To increase the size of the session table, refer to the section “Displaying and modifying system
parameter default settings” on page 578. The ip-qos-session parameter controls the size of the
session table.
IP Address Next Hop MAC Type Port Vlan Pri
1 192.168.1.11 DIRECT 0000.0000.0000 PU n/a 0