Alteon Application Switch Operating System Application Guide
Global Server Load Balancing
Document ID: RDWR-ALOS-V2900_AG1302
755
How Proxy IP Works
Figure 127 - POP3 Request Fulfilled via IP Proxy, page 755
illustrates two GSLB sites deployed in
San Jose and Denver. The applications being load balanced are HTTP and POP3. Any request that
cannot be serviced locally is sent to the peer site. HTTP requests are sent to the peer site using HTTP
redirect. Any other application request is sent to the peer site using the proxy IP feature.
Figure 127: POP3 Request Fulfilled via IP Proxy
The following procedure explains the three-way handshake between the two sites and the client for
a non-HTTP application (POP3):
1. A user POP3
TCP SYN
request is received by the virtual server at Site 2. Alteon at that site
determines that there are no local resources to handle the request.
2. The Site 2 Alteon rewrites the request such that it now contains a client proxy IP address as the
source IP address, and the virtual server IP address at Site 1 as the destination IP address.
3. Alteon at Site 1 receives the POP3
TCP SYN
request to its virtual server. The request looks like a
normal
SYN
frame, so it performs normal local load balancing.
4. Internally at Site 1, Alteon and the real servers exchange information. The
TCP SYN ACK
from
Site 1's local real server is sent back to the IP address specified by the proxy IP address.
5. The Site 1 Alteon sends the
TCP SYN ACK
frame to Site 2, with Site 1's virtual server IP address
as the source IP address, and Site 2's proxy IP address as the destination IP address.
6. Alteon at Site 1 receives the frame and translates it, using Site 1's virtual server IP address as
the source IP address and the client's IP address as the destination IP address.
This cycle continues for the remaining frames to transmit all the client's mail, until a FIN frame is
received.
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