IBM 8275-416, User Manual

Page: 19 / 156

router, as well as between any two switch ports. The switch monitors the traffic to
determine if a Layer 2 shortcut can be used instead of subjecting the packet to
Layer 3 router processing which can be relatively lengthy.
The Self Learning IP function essentially:
v
Learns the network structure, classifying attached devices as routers or hosts.
v
Maintains knowledge of network structure, aging out unused devices over time.
v
Expedites packet flow through the network by circumventing the router whenever
possible.
Device learning and classification is accomplished by watching ARP replies that
flow naturally through the switch with the addition of active probing to determining
whether a device is a router or a host. When an IP packet enters the switch, the
Self Learning IP function compares the destination MAC address against the list of
known routers, then checks if the destination IP address is a known host. If both
tests pass, the packet is automatically re-addressed to the destination IP host
device and is sent out the appropriate switch port.
A Router Table and Host Table are used to manage information learned about
router and host devices, respectively. To keep this network information current, the
Router Table entries are refreshed every 5 minutes while Host Table entries are
checked every 3 minutes. Devices which are no longer active are dropped from
their table; devices may be relearned at a later time as conditions change.
To use the Self Learning IP function, the switch must be configured with the
following:
v
IP information (see Network Connectivity Configuration Menu in Chapter 4).
Note: For the Self Learning IP function to work, the IP information must include
a default gateway for the network.
v
Enable the Self Learning IP function (see the Switch Configuration Menu in
Chapter 4).
Router
Switch
2.2.2.x
Subnet 1.1.1.x
Subnet
Server
Host A
1.1.1.10
* Host = clients or servers
Host B
2.2.2.20
Figure 1. Self-Learning IP in the network
Chapter 1. Introduction
3