Allied Telesis AT-S63 User Manual
Page 165
AT-S63 Management Software Menus Interface User’s Guide
Section I: Basic Operations
165
In cases where you select a load distribution that employs either a source
or destination address but not both, only the last three bits of the
designated address are used in selecting 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.
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.
A similar 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 the 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. The
binary values would be:
9 = 1001
3 = 0011
Applying the XOR rules above on the last three bits would result in 010, or
2. A examination of the table above shows that the packet would be
transmitted from port 9.
Last 3 Bits
000
(0)
001
(1)
010
(2)
011
(3)
100
(4)
101
(5)
110
(6)
111
(7)
Trunk Ports
7
8
9
10
11
12
13
14