Brocade FastIron Ethernet Switch Layer 3 Routing Configuration Guide - Manual (Page 26)

makes an entry in the session table or the forwarding cache, and sends the route to a queue on the
outgoing ports:
• ‐ If the running-config contains an IP access policy for the packet, the software makes an
entry in the session table. The Layer 3 switch uses the new session table entry to
forward subsequent packets from the same source to the same destination.
‐ If the running-config does not contain an IP access policy for the packet, the software
creates a new entry in the forwarding cache. The Layer 3 switch uses the new cache
entry to forward subsequent packets to the same destination.
The following sections describe the IP tables and caches:
• ARP cache and static ARP table
• IP route table
• IP forwarding cache
• Layer 4 session table
The software enables you to display these tables. You also can change the capacity of the tables
on an individual basis if needed by changing the memory allocation for the table.
ARP cache and static ARP table
The ARP cache contains entries that map IP addresses to MAC addresses. Generally, the entries are
for devices that are directly attached to the Layer 3 switch.
An exception is an ARP entry for an interface-based static IP route that goes to a destination that is
one or more router hops away. For this type of entry, the MAC address is either the destination device
MAC address or the MAC address of the router interface that answered an ARP request on behalf of
the device, using proxy ARP.
ARP cache
The ARP cache can contain dynamic (learned) entries and static (user-configured) entries. The
software places a dynamic entry in the ARP cache when the Layer 3 switch learns a device MAC
address from an ARP request or ARP reply from the device.
The software can learn an entry when the Layer 2 switch or Layer 3 switch receives an ARP request
from another IP forwarding device or an ARP reply. Here is an example of a dynamic entry:
IP Address MAC Address Type Age Port
1 10.95.6.102 0000.00fc.ea21 Dynamic 0 6
Each entry contains the destination device IP address and MAC address.
Static ARP table
In addition to the ARP cache, Layer 3 switches have a static ARP table. Entries in the static ARP table
are user-configured. You can add entries to the static ARP table regardless of whether or not the
device the entry is for is connected to the Layer 3 switch.
NOTE
Layer 3 switches have a static ARP table. Layer 2 switches do not.
The software places an entry from the static ARP table into the ARP cache when the entry interface
comes up.
ARP cache and static ARP table
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