Server Health Monitoring; Slb_Sat Rules - D-Link NetDefend DFL-210 User Manual

10.4.6. SLB_SAT Rules

10.4.5. Server Health Monitoring

SLB uses Server Health Monitoring to continuously check the condition of the servers in an SLB
configuration. SLB can monitor different OSI layers to check the condition of each server.
Regardless of the algorithms used, if a server is deemed to have failed, SLB will not open any more
connections to it until the server is restored to full functionality.
D-Link Server Load Balancing provides the following monitoring modes:
ICMP Ping
TCP Connection
10.4.6. SLB_SAT Rules
The key component in setting up SLB is the SLB_SAT rule in the IP rule set. The steps that should
be followed are:
1. Define an Object for each server for which SLB is to be done.
2. Define a Group which included all these objects.
3. Define an SLB_SAT Rule in the IP rule set which refers to this Group and where all other SLB
parameters are defined.
4. Define a further rule that duplicates the source/destination interface/network of the SLB_SAT
rule that allows traffic through. This could be one rule or a combination of:
• ForwardFast
• Allow
• NAT
The table below shows the rules that would be defined for a typical scenario of a set of webservers
behind the D-Link Firewall for which the load is being balanced. The Allow rule allows external
clients to access the webservers.
Rule Name
WEB_SLB
WEB_SLB_ALW Allow
If there are clients on the same network as the webservers that also need access to those webservers
then an NAT rule would also be used:
Rule Name
WEB_SLB
WEB_SLB_NAT
WEB_SLB_ALW Allow
Note that the destination interface is specified as core, meaning NetDefendOS itself deals with this.
The key advantage of having a separate Allow rule is that the webservers can log the exact IP
address that is generating external requests. Using only a NAT rule, which is possible, means that
This works at OSI layer 3. SLB will ping the IP address of each individual
server in the server farm. This will detect any failed servers.
This works at OSI layer 4. SLB attempts to connect to a specified port on
each server. For example, if a server is specified as running web services on
port 80, the SLB will send a TCP SYN request to that port. If SLB does not
receive a TCP SYN/ACK back, it will mark port 80 on that server as down.
SLB recognizes the conditions no response, normal response or closed port
response from servers.
Rule Type Src. Interface
SLB_SAT any
any
Rule Type Src. Interface
SLB_SAT any
NAT lan
any
Src. Network
all-nets
all-nets
Src. Network
all-nets
lannet
all-nets
405
Chapter 10. Traffic Management
Dest. Interface Dest. Network
core ip_ext
core ip_ext
Dest. Interface Dest. Network
core ip_ext
core ip_ext
core ip_ext