Cisco Catalyst 2000 Configuration Handbook page 174

g. (Optional) Hold connections open after no activity:
(virtual-server) idle duration
When SLB detects an absence of packets for a connection, it keeps the connec-
tion open for duration in seconds (IOS: 10 to 65,535; default 3600 seconds or 1
hour) before sending an RST.
h. (Optional) Prevent a SYN flood to the real servers:
(virtual-server) synguard syn-count [interval]
SLB monitors the number of SYNs that are received for the virtual server. If more
than syn-count (0 to 4294967295; default 0 or no SYN monitoring) SYNs are
received within the interval (50 to 5000 milliseconds; default 100 ms), any sub-
sequent SYNs are dropped.
i. (Optional) Control the advertisement of the virtual server:
(virtual-server) advertise [active]
By default, SLB creates a static route for the virtual server address to the Null0
logical interface. This static route can then be redistributed and advertised by a
routing protocol. The active keyword causes the route to be advertised only
when at least one real server is available. You can disable the advertisement with
no advertise, preventing the static route from being created.
j. Enable SLB to begin using the virtual server:
(virtual-server) inservice [standby group-name]
By default, the virtual server is not used by SLB unless it is placed in service. To
remove a virtual server from service, use no inservice.
Tip You can use multiple IOS SLB devices to provide redundancy for virtual servers. IOS
SLB stateless backup enables each SLB device to listen to HSRP messages from Layer 3
interfaces on redundant switches. When one switch (and its IOS SLB) fails, another HSRP
interface becomes the primary gateway. When the other IOS SLB also detects the failure,
the virtual servers that are associated with the HSRP group-name (defined previously)
become active. No SLB state information is kept, however, so existing connections are
dropped and must be reestablished.
Stateless backup requires that HSRP be configured on all the redundant Layer 3 devices on
the server-side VLAN. Be sure that the group-name matches between the HSRP and vir-
tual server configurations. See section "8-6: Router Redundancy with HSRP" in Chapter 8,
"Configuring High Availability Features," for further HSRP configuration information.
k. (Optional) Use SLB stateful backup:
(virtual-server) replicate casa listening-ip remote-ip port-number
[interval] [password [0|7] password [timeout]]
IOS SLB replicates and exchanges its load-sharing decision tables with other
stateful backup devices using the Cisco Appliance Services Architecture
Chapter 10: Server Load Balancing (SLB) 153