Cisco Cisco IOS Software Release 12.2(18)SXE
Features
12
Cisco IOS Release 12.2(18)SXE
Session Redirection
Session redirection involves redirecting packets to real servers. IOS SLB can operate in one of two
session redirection modes, dispatched mode or directed mode.
session redirection modes, dispatched mode or directed mode.
Note
In both dispatched and directed modes, IOS SLB must track connections. Therefore, you must design
your network so that there is no alternate network path from the real servers to the client that bypasses
the load-balancing device.
your network so that there is no alternate network path from the real servers to the client that bypasses
the load-balancing device.
Dispatched Mode
In dispatched mode, the virtual server address is known to the real servers; you must configure the virtual
server IP address as a loopback address, or secondary IP address, on each of the real servers. IOS SLB
redirects packets to the real servers at the media access control (MAC) layer. Since the virtual server IP
address is not modified in dispatched mode, the real servers must be Layer 2-adjacent to IOS SLB, or
intervening routers might not be able to route to the chosen real server.
server IP address as a loopback address, or secondary IP address, on each of the real servers. IOS SLB
redirects packets to the real servers at the media access control (MAC) layer. Since the virtual server IP
address is not modified in dispatched mode, the real servers must be Layer 2-adjacent to IOS SLB, or
intervening routers might not be able to route to the chosen real server.
For Catalyst 6500 family switches, dispatched mode with hardware data packet acceleration generally
yields better performance than directed mode.
yields better performance than directed mode.
Refer to the “Configuring Logical Interfaces” chapter of the Cisco IOS Interface Configuration Guide,
Release 12.2 for more information about configuring the loopback address.
Release 12.2 for more information about configuring the loopback address.
Directed Mode
In directed mode, the virtual server can be assigned an IP address that is not known to any of the real
servers. IOS SLB translates packets exchanged between a client and a real server, using NAT to translate
the virtual server IP address to a real server IP address.
servers. IOS SLB translates packets exchanged between a client and a real server, using NAT to translate
the virtual server IP address to a real server IP address.
IOS SLB supports the following types of NAT:
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Note
You can use both server NAT and client NAT for the same connection.
IOS SLB does not support FTP or firewall load balancing in directed mode. Therefore, FTP and firewall
load balancing cannot use NAT.
load balancing cannot use NAT.
IOS SLB supports only client NAT for TCP and UDP virtual servers.
IOS SLB supports only server NAT (but not server port translation) for Encapsulation Security Payload
(ESP) virtual servers or Generic Routing Encapsulation (GRE) virtual servers.
(ESP) virtual servers or Generic Routing Encapsulation (GRE) virtual servers.
Server NAT
Server NAT involves replacing the virtual server IP address with the real server IP address (and vice
versa). Server NAT provides the following benefits:
versa). Server NAT provides the following benefits:
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Servers can be many hops away from the load-balancing device.
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Intervening routers can route to them without requiring tunnelling.
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Loopback and secondary interfaces are not required on the real server.