Alteon Application Switch Operating System Application Guide
Server Load Balancing
Document ID: RDWR-ALOS-V2900_AG1302 199
One Arm SLB Configuration
In a one-arm SLB configuration, you must enable MAC address substitution to avoid session failure.
As illustrated in Figure 33 - One Arm Topology, page 199, in a one-arm configuration, the client and
server are on same broadcast domain but have different IP address ranges.
Figure 33: One Arm Topology
Because in this configuration delayed binding (dbind) is enabled, you must force the reply traffic
from the server to go back through Alteon for correct session conversion. This is performed through
routing and not proxy IP (PIP), which forces the traffic to return though Alteon without making
changes on the server.
In this configuration, everything works properly on the server side. The server receives packets with
the client's source MAC address, and because it has a different IP range than the client, the server
correctly returns the traffic to the client. However, the packets fail to reach the client because both
Alteon and the Layer 2 switch are located on the same broadcast domain. This results in Alteon
forwarding packets from the client on a different port on the Layer 2 switch, with the MAC address
acting like a floating address, meaning that first the Layer 2 switch reads the client MAC address on
the client's physical port, and then it reads it on the Alteon physical port.
When enabling source MAC substitution, the packets sent from an Alteon only use Alteon's MAC
address, so the client MAC address "remains" on the client port of the switch.
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