Coyote Point Systems Equalizer Spezifikationen PDF herunterladen (Seite 33)

to one of Equalizer’s IP addresses before forwarding packets to a server. The servers will send responses

back to Equalizer’s IP (so it is usually not necessary to set Equalizer as the default gateway on the servers

when spoof is disabled).

Match rules can be used to selectively apply the spoof option to client requests. This is sometimes called

selective SNAT

. See the section "Changing the Spoof (SNAT) Setting Using Match Rules" on page 340 .

3. When a server sends a response to a client request through Equalizer, the NAT subsystem

always

translates the source IP in the response packets (that is, the server IP) to the cluster IP to which the client

originally sent the request. This is necessary since the client sent its original request to the cluster IP and

will not recognize the server’s IP address as a response to its request -- instead, it will drop the packet.

4. NAT can also be enabled for packets that

originate

on the servers behind Equalizer and are destined for

subnets other than the subnet on which the servers reside -- on Equalizer, this is called

outbound NAT

. This

is usually required in dual network mode when reserved IP addresses (e.g., 10.x.x.x, 192.168.x.x) are being

used on the internal interface, so that the recipients do not see reserved IP addresses in packets originating

from the servers. When the global outbound NAT option is enabled, Equalizer translates the source IP in

packets from the servers that are not part of a client connection to the Equalizer’s Default VLAN IP address

(the external interface IP address on the E250GX and legacy ‘si’ systems), or to the address specified in

the server’s Outbound NAT tab. Enabling outbound NAT, as a result, has a performance cost since

Equalizer is examining every outbound packet.

Note - When Equalizer is in single network mode, outbound NAT should be

disabled

. Since Equalizer resides on a

single subnet, outbound NAT is not needed, and may cause unexpected behavior.

Note that when Equalizer receives a packet that is not destined for a virtual cluster IP address, a failover IP

address, a client IP address on an open connection, or one of its own IP addresses, Equalizer passes the packet

through to the destination network unaltered.

l For more information about setting NAT and spoofing options, see "Clusters" on page 259.

How a Server is Selected

The main functionality of Equalizer is to load-balance-- that is that when a request is received from a client an

appropriate server for to connect the request with. The "appropriate" server is usually selected as part of a

proprietary load balancing algorithm or via round-robin. Another factoring into server selection is "persistence". If a

client connection has persistence associated with it, the server to which the persists should be selected for load

balancing If the server selected by persistence is not available, Equalizer uses load balancing policy to select an

alternate server.

Load Balancing

Load balancing is based on the policy selected. The policies can be split up into two categories – round robin and

everything else. The round robin simply selects the next server in the list with no regard for how busy that server

may be. The other load balancing policies use proprietary algorithms to compute the load of a server and then

select the server with the least load server.

Although the load balancing policies are proprietary, they use the following factors in their calculation:

Equalizer Administration Guide

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