Brocade FastIron Ethernet Switch Layer 3 Routing Configuration Guide - Manual (Page 28)

• 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.
IP Address Next Hop MAC Type Port Vlan Pri
1 192.168.1.11 DIRECT 0000.0000.0000 PU n/a 0
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.
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" in the FastIron Ethernet Switch Platform and Layer 2 Switching Configuration Guide .
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" in the FastIron Ethernet Switch Platform and Layer 2 Switching
Configuration Guide . The ip-qos-session parameter controls the size of the session table.
IP route exchange protocols
Brocade Layer 3 switches support the following IP route exchange protocols:
• Routing Information Protocol (RIP)
• Open Shortest Path First (OSPF)
• Border Gateway Protocol version 4 (BGP4)
All these protocols provide routes to the IP route table. You can use one or more of these protocols, in
any combination. The protocols are disabled by default.
Layer 4 session table
28 FastIron Ethernet Switch Layer 3 Routing Configuration Guide
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