Module 2 Server Load Balancing

Server Load
Balancing

Slide 1

Objectives
Understand SLB frame flow & Client/Server
processing
Understand the different
load balancing algorithms

Understand server health checks

Understand SLB configurations

Slide 2

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
Real Server Port (rport) – Defines the real server TCP or UDP port
assigned to the service

Slide 3

Review of IP Communication
and HTTP Requests

Slide 4

IP Communication

L2 Header
– MAC Source Address
– MAC Destination Address
– Checksum

Layer
2

Source MAC

Source MAC

Destination MAC

VIP MAC

Source IP

Client IP

Destination IP

VIP

Checksum

B35C

Source Port

2165

Destination Port

80

Checksum

037A

IP Header
– IP Source Address
– IP Destination Address
– Checksum

Layer
3

TCP Header
– Source Port
– Destination Port
– Checksum

Session ID
– IP Source Address
– Source Port

Layer
4

Slide 5

The Life of an HTTP Request
DNS
DNS Lookup
Lookup for:
for: www.appswitch.com
www.appswitch.com

Client
Client

DNS
DNS response
response with:
with: 192.168.13.10
192.168.13.10

Client
Client Site

Site DNS
DNS
Server
Server

IPDA
IPDA 192.168.13.10:
192.168.13.10: TCP
TCP SYN,
SYN, Dest
Dest TCP
TCP Port
Port 80
80

Client
Client

IPDA
IPDA (client)

(client) :: TCP
TCP SYN-ACK
SYN-ACK
IPDA
IPDA 192.168.13.10:
192.168.13.10: SYN
SYN ACK-ACK,
ACK-ACK, TCP
TCP Port
Port 80
80

Web
Web Server
Server

IPDA
IPDA 192.168.13.10:
192.168.13.10: HTTP
HTTP GET

GET (url),
(url), TCP
TCP Port
Port 80
80
IPDA
IPDA (client)
(client) :: GET
GET RESPONSE
RESPONSE (data)
(data)
IPDA
IPDA 192.168.13.10:TCP
192.168.13.10:TCP FIN,
FIN, Dest
Dest TCP
TCP Port
Port 80
80
IPDA

IPDA (client)
(client) :: TCP
TCP FIN-ACK
FIN-ACK
Slide 6

Basic Frame Flow & Client and
Server Processing

Slide 7

Basic Frame Flow Process
(1) DNS resolves
incoming request
to switch.

Network Manager

DNS
www.appswitch.com ~ 192.100.13.10

10.10.10.1
VIP 192.100.13.10
Port 80
client proc.

10.10.10.2

server proc.
(2) Switch selects best server
based on policy.

10.10.10.3

(3) Response is sent to client
via switch.
Slide 8

VIP

192.100.13.0/28

VIP 192.100.13.10

Client: 1.2.3.4:2000

10.10.10.0/24
10.10.10.1

10.10.10.2

10.10.10.3

Slide 9

Proper Routing

192.100.13.1/28
VIP 192.100.13.10

Client: 1.2.3.4:2000

Ensure proper routing

10.10.10.0/24
10.10.10.1

10.10.10.2

10.10.10.3

Slide 10

Accessing the VIP
Network Manager

DNS
www.appswitch.com ~ 192.100.13.10

VIP 192.100.13.10
Port 80

Client: 1.2.3.4:2000
DestIP: 192.100.13.10:80

Access virtual-server IP-address/service

10.10.10.1

10.10.10.2

10.10.10.3

Slide 11

Detect Request

SrcIP : 1.2.3.4:2000
DestIP: 192.100.13.10:80

VIP 192.100.13.10
Port 80

Client: 1.2.3.4:2000
DestIP: 192.100.13.10:80

client process

Detect request to virtual-server IP-address/service

10.10.10.1

10.10.10.2

10.10.10.3

Slide 12

Is request already served?
Connection Table
Source client-IP:port
Dest.
VIP: service-port

VIP 192.100.13.10
Port 80

Client: 1.2.3.4:2000

client process

Is current request already served?

10.10.10.1

10.10.10.2

10.10.10.3

Slide 13

Yes, Request Already Served
Connection Table
Source client-IP:port
Dest.
VIP: service-port
LoadB. Rserver:listen-port
Protocol
client process
VIP 192.100.13.10
Port 80

Client: 1.2.3.4:2000

Is current request already served? Yes, send to servers.

10.10.10.1

10.10.10.2

10.10.10.3

Slide 14

No, Do Load Balancing
Connection Table
Source client-IP:port
Dest.
VIP: service-port

VIP 192.100.13.10
Port 80

Client: 1.2.3.4:2000

client process

Is current request already served? No, do load balancing

10.10.10.1

10.10.10.2

10.10.10.3

Slide 15

Send Request to Real Server
Connection Table
Source client-IP:port
Dest.
VIP: service-port
LoadB. Rserver:listen-port
Protocol
client process
VIP 192.100.13.10
Port 80

10.10.10.1

10.10.10.2

Client: 1.2.3.4:2000
SrcIP: 1.2.3.4:2000
DestIP: 10.10.10.3:80

Send request to real-server

10.10.10.3

Slide 16

Real Server Responds
Connection Table

Service Map Table

Source client-IP:port
Dest.
VIP: service-port
LoadB. Rserver:listen-port
Protocol

VIP - Real-server 1
…
VIP - Real-server x

VIP 192.100.13.10
Port 80

10.10.10.1

server
process
10.10.10.2

Client: 1.2.3.4:2000
SrcIP:10.10.10.3:80
DestIP: 1.2.3.4:2000

Real-server responds

10.10.10.3

Slide 17

NAT Real to Virtual IP
Connection Table

Service Map Table

Source client-IP:port
Dest.
VIP: service-port
LoadB. Rserver:listen-port
Protocol

VIP - Real-server 1
…
VIP - Real-server x

VIP 192.100.13.10
Port 80

10.10.10.1

server
process
Client: 1.2.3.4:2000

10.10.10.2
SrcIP:192.100.13.10:80
DestIP: 1.2.3.4:2000
SrcIP:10.10.10.3:80
DestIP: 1.2.3.4:2000

NAT real to virtual IP

10.10.10.3

Slide 18

Client Processing

MAC
MAC

IP
IP

TCP
TCP

Dst MAC
Src MAC
Src IP Address
Dst IP Address

Src Port
Dst Port

virt_mac
router_mac

rip_mac

rip_mac

router_mac

router_mac

CIP
VIP

CIP
VIP

CIP
RIP

CIP
RIP

2155
80

2155
80

2155
80

2155
80

Client

Application Switch

Real Server

Client processing is enabled on a per-port basis under /cfg/slb/port #/client ena.
For SLB traffic, switch uses a different mac address: aa:bb:cc:dd:ee:xe
Slide 19

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.
Packets not addressed to a VIP are switched at L2.

Slide 20

Server Processing

MAC
MAC

IP
IP

TCP
TCP

SrcMAC
DestMAC

vip_mac
router_mac

rip_mac

rip_mac

router_mac

router_mac

Src IP Address
Dst IP Address

VIP
CIP

VIP
CIP

RIP
CIP

RIP
CIP

Src Port
Dst Port

80
2155

80
2155

80
2155

80
2155

Client

Application Switch

Real Server

Server processing is enabled on a per-port basis under /cfg/slb/port #/server ena.

Slide 21

Server-to-Client Traffic
All packets must be “watched.”
Determine whether arriving packets are
associated with virtual services or native
communications.
Implement Source IP/s-port substitution if
the packet is associated with a virtual
service.
Use service map table
Forward using L2 switching if the packet is
not associated with a virtual service.
Slide 22

Appdirector to Alteon Dictionary
 

AppDirector, CID
Farm
 
Dispatch Method
Client Table

Server
 
Port Multiplexing
Session Table Mode "entry per
session"

=
=
=
=
=
=

Backup Server
=
1 to 1 BS  
=
Layer 4 policy
~
Client Aging Time
=
Transparent LB (CID/SF)
=
Application Server Support (spoof
SIP)
=
Dyn NAT/Client NAT

=

 
Alteon
Group
Metric
Session Table
RIP (real
IP)
Rport

 
 
 
 
 
 

DAM (Direct Access Mode)
Service Group
Backup
 
Real Server Backup  
Combination of VIP + Service
Ptimer (Persistency Timer)
Filtering (action: redirect)
RTS (Return to
Sender)
 
PIP (Proxy IP
Addressing )
 
Slide 23

Proceed to Module 2a – Server
Load Balancing – LB Algorithms

Slide 24

Thank You!
www.radware.com