Objectives
Understand SLB frame flow & Client/Server
processing
Understand the different
load balancing algorithms
Understand server health checks
Alteon SLB Terminology
Real Server – Actual server connecting to (Must be enabled)
Real IP (RIP) – Real server IP Address
Group – Group of real servers for load balancing (Doesn’t need to be
enabled)
Virtual Server – All client requests are forwarded to the virtual server
defined on the Alteon
Virtual IP (VIP) – IP address of the virtual server on the Alteon
Metrics – Used to select which real server in a group receives the client
request
Weights – Bias load balancing to give the fastest real servers a larger
share of connections
IP Communication
L2 Header
–
MAC Source Address
–
MAC Destination Address
–
Checksum
IP Header
–
IP Source Address
–
IP Destination Address
–
Checksum
TCP Header
–
Source Port
–
Destination Port
–
Checksum
Session ID
–
IP Source Address
Layer
2 Source MAC Source MAC Destination MAC VIP MAC
Layer
3 Source IP Client IP Destination IP VIP
Checksum B35C
Layer
4 Source Port 2165 Destination Port 80
The Life of an HTTP Request
IPDA 192.168.13.10: SYN ACK-ACK, TCP Port 80 IPDA 192.168.13.10: SYN ACK-ACK, TCP Port 80 Client
Client Client Site DNS Server
Client Site DNS Server DNS Lookup for: www.appswitch.com
DNS Lookup for: www.appswitch.com
DNS response with: 192.168.13.10 DNS response with: 192.168.13.10
Client Client
Web Server Web Server IPDA 192.168.13.10: TCP SYN, Dest TCP Port 80
IPDA 192.168.13.10: TCP SYN, Dest TCP Port 80
IPDA (client) : TCP SYN-ACK IPDA (client) : TCP SYN-ACK
IPDA 192.168.13.10: HTTP GET (url), TCP Port 80 IPDA 192.168.13.10: HTTP GET (url), TCP Port 80
IPDA (client) : GET RESPONSE (data) IPDA (client) : GET RESPONSE (data)
IPDA 192.168.13.10:TCP FIN, Dest TCP Port 80 IPDA 192.168.13.10:TCP FIN, Dest TCP Port 80
Basic Frame Flow Process
DNS
www.appswitch.com ~ 192.100.13.10 Network Manager
(2) Switch selects best server based on policy.
(3) Response is sent to client via switch.
VIP 192.100.13.10 Port 80
10.10.10.1
10.10.10.2
10.10.10.3 (1) DNS resolves
incoming request to switch.
client proc.
VIP
10.10.10.1
10.10.10.2
10.10.10.3 Client: 1.2.3.4:2000
VIP 192.100.13.10
Proper Routing
VIP 192.100.13.10
10.10.10.1
10.10.10.2
10.10.10.3 10.10.10.0/24
192.100.13.1/28
Ensure proper routing
Accessing the VIP
DNS
www.appswitch.com ~ 192.100.13.10 Network Manager
10.10.10.1
10.10.10.2
10.10.10.3
Access virtual-server IP-address/service
Client: 1.2.3.4:2000
DestIP: 192.100.13.10:80
Detect Request
10.10.10.1
10.10.10.2
10.10.10.3
Detect request to virtual-server IP-address/service
Client: 1.2.3.4:2000
DestIP: 192.100.13.10:80
SrcIP : 1.2.3.4:2000
DestIP: 192.100.13.10:80
VIP 192.100.13.10 Port 80
Is request already served?
10.10.10.1
10.10.10.2
10.10.10.3
Is current request already served?
Client: 1.2.3.4:2000 client process
VIP 192.100.13.10 Port 80
Connection
Table
Yes, Request Already Served
10.10.10.1
10.10.10.2
10.10.10.3
Is current request already served? Yes, send to servers.
Client: 1.2.3.4:2000
Connection Table
Source
client-IP:port
Dest
.
VIP: service-port
LoadB
.
Rserver:listen-port
Protocol
client process
No, Do Load Balancing
Is current request already served? No, do load balancing
10.10.10.1
10.10.10.2
10.10.10.3
Client: 1.2.3.4:2000 client process
VIP 192.100.13.10 Port 80
Connection
Table
Connection Table
Source client-IP:port
Dest.
VIP: service-port
LoadB. Rserver:listen-port
Protocol
Send Request to Real Server
10.10.10.1
10.10.10.2
10.10.10.3
Send request to real-server
Client: 1.2.3.4:2000
SrcIP: 1.2.3.4:2000 DestIP: 10.10.10.3:80 client process
Real Server Responds
10.10.10.1
10.10.10.2
10.10.10.3
Real-server responds
server process
Client: 1.2.3.4:2000
VIP 192.100.13.10 Port 80
SrcIP:10.10.10.3:80 DestIP: 1.2.3.4:2000
Service Map Table
VIP - Real-server 1
…
VIP - Real-server x
Connection Table
NAT Real to Virtual IP
10.10.10.1
10.10.10.2
10.10.10.3
NAT real to virtual IP
server process
Client: 1.2.3.4:2000
SrcIP:192.100.13.10:80 DestIP: 1.2.3.4:2000
VIP 192.100.13.10 Port 80
SrcIP:10.10.10.3:80 DestIP: 1.2.3.4:2000
Service Map Table
VIP - Real-server 1
…
VIP - Real-server x
Connection Table
Client Processing
Src MAC
Src IP Address Dst IP Address
Src Port Dst Port
CIP
Application Switch
rip_mac
Real Server
Client processing is enabled on a per-port basis under /cfg/slb/port #/client ena.
Client-to-Server Traffic
Recognize received SYN packet addressed to a VIP (TCP
connection request).
•
Is session table entry present?
•
If no entry, do slb.
•
Bind session and create session ID entry.
•
IP address substitution based on Session ID
Recognize successive packets associated with the same
session and send to the same real server.
Unbind upon reception of a FIN packet or time-out.
Server Processing
Src IP Address Dst IP Address
Src Port Dst Port
VIP
Application Switch
rip_mac
Real Server
