Cisco Systems 78-11741-02 Port-Bound Servers, Client-Assigned Load Balancing, Sticky Connections

Configuring Server Load Balancing

IOS SLB Functions and Capabilities

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.

Packets destined for a virtual server address for a port that is not specified in the virtual server definition are not redirected.

IOS SLB supports both port-bound and nonport-bound servers, but port-bound servers are recommended.

Client-Assigned Load Balancing

Client-assigned load balancing allows you to limit access to a virtual server by specifying the list of client IP subnets that are permitted to use that virtual server. With this feature, you can assign a set of client IP subnets (such as internal subnets) connecting to a virtual IP address to one server farm, and assign another set of clients (such as external clients) to a different server farm.

Content Flow Monitor Support

IOS SLB supports the Cisco Content Flow Monitor (CFM), a Web-based status monitoring application within the CiscoWorks2000 product family. You can use CFM to manage Cisco server load-balancing devices. CFM runs on Windows NT and Solaris workstations, and is accessed using a Web browser.

Sticky Connections

When you use sticky connections, new connections from a client IP address or subnet are assigned to the same real server as were previous connections from that address or subnet.

IOS SLB creates sticky objects to track client assignments. The sticky objects remain in the IOS SLB database after the last sticky connection is deleted, for a period defined by a configurable sticky timer. If the timer is configured on a virtual server, new connections from a client are sent to the same real server that handled the previous client connection, provided one of the following conditions is true:

•A connection for the same client already exists.

•The amount of time between the end of a previous connection from the client and the start of the new connection is within the timer duration.

Sticky connections also permit the coupling of services that are handled by more than one virtual server. This allows connection requests for related services to use the same real server. For example, Web server (HTTP) typically uses TCP port 80, and HTTP over Secure Socket Layer (HTTPS) uses port 443. If HTTP virtual servers and HTTPS virtual servers are coupled, connections for ports 80 and 443 from the same client IP address or subnet are assigned to the same real server.

Maximum Connections

The maximum connections feature allows you to configure a limit on the number of active connections that a real server can handle.

Cisco IOS IP Configuration Guide

IPC-136