Cisco Systems 78-11741-02 manual Troubleshooting IOS SLB, Question Answer, IPC-150

Configuring Server Load Balancing

IOS SLB Configuration Task List

Troubleshooting IOS SLB

Table 6 lists questions and answers that can help you troubleshoot IOS SLB.

Table 6	IOS SLB Troubleshooting Guidelines
Question		Answer
Why can I connect to real servers directly, but not		Make sure that the virtual IP address is configured as a loopback in each
to the virtual server?		of the real servers (if you are running in dispatched mode).
Why is IOS SLB not marking my real server as		Tune the values for the numclients, numconns, and delay keywords.
failed when I disconnect it from the network?		If you have a very small client population (for example, in a test
		environment), the numclients keyword could be causing the problem.
		This parameter prevents IOS SLB from mistaking the failure of a small
		number of clients for the failure of a real server.
Why is IOS SLB not marking my connections as		If you are using dispatched mode, make sure there are no alternate paths
established even though I am transferring data?		that allow outbound flows to bypass IOS SLB. Also, make sure that the
		clients and real servers are not on the same IP subnet.
Why does IOS SLB show my real server as		The inservice and outofservice states indicate whether the network
inservice even though I have taken it down or		administrator intends for that real server to be used when it is operational.
physically disconnected it?		A real server that was inservice but was removed from the selection list
		dynamically by IOS SLB as a result of automatic failure detection, is
		marked as failed. Use the show ip slb reals detail EXEC command to
		display these real server states.
		Beginning with Cisco IOS Release 12.1(1)E, the inservice keyword is
		changed to operational, to better reflect actual condition.
Why is IOS SLB not balancing correctly? I am		Enter the show mls flow command:
using dispatched mode, the servers are leaving		Router# show mls flow
sockets open, and I am seeing RSTs in response
to a number of SYNs. Curiously, sometimes		current ip flowmask for unicast: full flow
things work fine.		current ipx flowmask for unicast: destination only
		The current IP flowmask must be full flow. If it is not, correct the problem
		using the mls flow ip full global configuration command:
		Router# configure terminal
		Enter configuration commands, one per line.
		End with CNTL/Z.
		Router(config)# mls flow ip full
		Router(config)#

Cisco IOS IP Configuration Guide

IPC-150