Allied Telesis AT-S62 User Manual

Page 131

AT-S62 Menus Interface User’s Guide

Section I: Basic Operations

131

❑ Source IP Address / Destination IP Address (Layer 3)

The load distribution methods examine the last three bits of a packet’s
MAC or IP address and compare the bits against mappings assigned to
the ports in the trunk. The port mapped to the matching bits is selected
as the transmission port for the packet.

In cases where you select a load distribution that employs either a
source or destination address but not both, the last three bits of only the
designated address are used in the selection of a transmission port in a
trunk. If you select one of the two load distribution methods that
employs both source and destination addresses, port selection is
achieved through an XOR operation of the last three bits of both
addresses.

As an example, assume you created a static or LACP aggregate trunk of
Ports 7 to 14 on a switch. The table below shows the mappings of the
switch ports to the possible values of the last three bits of a MAC or IP
address.

Now assume you selected source MAC address as the load distribution
method and that the switch needed to transmit over the trunk a packet
with a source MAC address that ended in 9. The binary equivalent of 9 is
1001, making the last three bits of the address 001. An examination of
the table above indicates that the switch would use Port 8 to transmit
the frame because that port is mapped to the matching bits.

The same method is used for the two load distribution methods that
employ both the source and destination addresses. Only here the last
three bits of both addresses are combined by an XOR process to derive a
single value which is then compared against the mappings of bits to
ports. The XOR rules are as follows:

0 XOR 0 = 0

0 XOR 1 = 1

1 XOR 0 = 1

1 XOR 1 = 0

As an example, assume that you had selected source and destination
MAC addresses for the load distribution method in our previous
example, and that a packet for transmission over the trunk had a source
MAC address that ended in 9 and a destination address that ended in 3.

Last 3 Bits

000
(0)

001
(1)

010
(2)

011
(3)

100
(4)

101
(5)

110
(6)

111
(7)

Trunk Ports