Cisco Cisco IOS Software Release 12.2(18)SXF
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IOS Server Load Balancing Feature in IOS Release 12.2(18)SXF7
Features
IOS SLB uses the following logic when handling a packet from a real server:
Step 1
Does the packet match a real server?
•
If no, IOS SLB has no interest in the packet.
•
If yes, continue.
Step 2
Does the packet match an existing connection?
•
If yes, IOS SLB uses NAT to redirect the packet, in accordance with the connection control block.
•
If no, continue.
Step 3
Is the real server configured to use static NAT?
•
If no, IOS SLB handles the packet as usual. This functionality is also called static NAT
pass-through.
pass-through.
•
If yes, continue.
Step 4
Is the real server configured to have its packets dropped by IOS SLB, if the packets do not correspond
to existing connections?
to existing connections?
•
If yes, IOS SLB drops the packet.
•
If no, continue.
Step 5
Is the real server configured for per-packet server load balancing?
•
If yes, IOS SLB uses NAT to redirect the packet.
•
If no, continue.
Step 6
Is the real server configured to maintain connection state for sticky connections?
•
If no, IOS SLB builds the connection.
•
If yes, IOS SLB searches for a matching sticky object. Continue.
Step 7
Can IOS SLB find a matching sticky object?
•
If no, IOS SLB drops the packet.
•
If yes, IOS SLB builds the connection.
Server Port Translation
Server port translation, also known as port address translation, or PAT, is a form of server NAT that
involves the translation of virtual server ports instead of virtual server IP addresses. Virtual server port
translation does not require translation of the virtual server IP address, but you can use the two types of
translation together.
involves the translation of virtual server ports instead of virtual server IP addresses. Virtual server port
translation does not require translation of the virtual server IP address, but you can use the two types of
translation together.
IOS SLB supports server port translation for TCP and UDP only.
Port-Bound Servers
When you define a virtual server, you must specify the TCP or UDP port handled by that virtual server.
However, if you configure NAT on the server farm, you can also configure port-bound servers.
Port-bound servers allow one virtual server IP address to represent one set of real servers for one service,
such as HTTP, and a different set of real servers for another service, such as Telnet.
However, if you configure NAT on the server farm, you can also configure port-bound servers.
Port-bound servers allow one virtual server IP address to represent one set of real servers for one service,
such as HTTP, and a different set of real servers for another service, such as Telnet.
Packets destined for a virtual server address for a port that is not specified in the virtual server definition
are not redirected.
are not redirected.