Cisco has announced the end of sale for the Cisco LocalDirector. For more information, refer to the LocalDirector 400 Series End-of-Life and End-of-Sale Notices and Bulletins.
This document explains how to configure Domain Name System (DNS) probe functionality on a Cisco LocalDirector. The DNS probe allows LocalDirector to automatically fail or recover real servers that are running DNS servers, based on probe results. Probes are constantly sent to the DNS servers, to determine their status. If a DNS server fails to respond to a certain number of probes, it is marked as Failed External (EFAILED). As soon as the DNS server starts to respond to DNS probes again, it is returned to the in-service state. The configuration in this document also shows how you can load balance other ports on the same servers while you are probing DNS.
There are no specific requirements for this document.
The information in this document is based on these software and hardware versions:
LocalDirector software version 4.2.1
Microsoft Windows 2000 server running DNS with an “A” record entry for the virtual IP (VIP) address.
The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, make sure that you understand the potential impact of any command.
Refer to Cisco Technical Tips Conventions for more information on document conventions.
This document uses this network setup:
Use these steps to configure the LocalDirector:
Configure all ports for a virtual User Datagram Protocol (UDP).
virtual 172.18.124.208:0:0:udp is
Configure port-specific real servers for DNS (such as 53).
real 172.18.124.193:53:0:udp is real 172.18.124.192:53:0:udp is
Bind the virtual servers to the real servers.
bind 172.18.124.208:0:0:udp 172.18.124.193:53:0:udp bind 172.18.124.208:0:0:udp 172.18.124.192:53:0:udp
Configure the probe.
For example, it is assumed that an “A” record is configured on the DNS with the virtual information.
probe real 172.18.124.193:53:0:udp dns 3 probedns nodename vip.testdomain.com probeconfig dns 4
Use this section to confirm that your configuration works properly.
The show version command displays the software version that is running on the LocalDirector.
LDIR-416# show version LocalDirector 416 Version 4.2.1
The show running-config command displays the configuration that is running on the LocalDirector.
LDIR-416# show running-config : Saved : LocalDirector 416 Version 4.2.1 syslog output 23.7 no syslog console enable password dfeaf10390e560aea745ccba53e044 encrypted hostname LDIR-416 no shutdown ethernet 0 no shutdown ethernet 1 shutdown ethernet 2 interface ethernet 0 auto interface ethernet 1 auto interface ethernet 2 auto mtu 0 1500 mtu 1 1500 mtu 2 1500 multiring all no secure 0 no secure 1 no secure 2 ping-allow 0 ping-allow 1 ping-allow 2 ip address 172.18.124.210 255.255.255.0 route 0.0.0.0 0.0.0.0 172.18.124.1 1 arp timeout 30 no rip passive rip version 1 failover ip address 0.0.0.0 no failover failover hellotime 30 password dfeaf10390e560aea745ccba53e044ed encrypted telnet 172.18.124.0 255.255.255.0 telnet 220.127.116.11 255.0.0.0 snmp-server enable traps snmp-server community public no snmp-server contact no snmp-server location virtual 172.18.124.208:80:0:tcp is virtual 172.18.124.208:0:0:udp is real 172.18.124.192:80:0:tcp is real 172.18.124.193:80:0:tcp is real 172.18.124.193:53:0:udp is real 172.18.124.192:53:0:udp is bind 172.18.124.208:80:0:tcp 172.18.124.192:80:0:tcp bind 172.18.124.208:80:0:tcp 172.18.124.193:80:0:tcp bind 172.18.124.208:0:0:udp 172.18.124.193:53:0:udp bind 172.18.124.208:0:0:udp 172.18.124.192:53:0:udp probe virtual 172.18.124.208:0:0:udp dns 3 probe real 172.18.124.193:53:0:udp dns 3 probe real 172.18.124.192:53:0:udp dns 3 probedns nodename vip.testdomain.com probeconfig dns 4
The show bind command displays which real servers are bound to which virtual servers.
LDIR-416# show bind Virtual Machine(s) Real Machine(s)/Urls 172.18.124.208:80:0:tcp(IS) 172.18.124.192:80:0:tcp(IS) 172.18.124.193:80:0:tcp(IS) 172.18.124.208:0:0:udp(IS) 172.18.124.193:53:0:udp(IS) 172.18.124.192:53:0:udp(IS)
The show virtual command displays a list of virtual servers, their states, their number of connections, and their load-balancing algorithms.
LDIR-416# show virtual Machines: Machine Mode State Connect Sticky Predictor Slowstart 172.18.124.208:80:0:tcp directed local IS 0 0 leastconns* roundrobin 172.18.124.208:0:0:udp directed local IS 0 0 leastconns* roundrobin
The show real command displays the statistics and states of the real servers.
LDIR-416# show real Real Machines No Answer TCP Reset DataIn Machine Connect State Thresh Reassigns Reassigns Conns 172.18.124.192:80:0:tcp 0 IS 8 0 0 0 172.18.124.193:80:0:tcp 0 IS 8 0 0 0 172.18.124.193:53:0:udp 172.18.124.192:53:0:udp
The show statistics command displays the real and virtual server statistics.
LDIR-416# show statistics Real Machine(s) Bytes Packets Connections 172.18.124.192:80:0:tcp 0 0 0 172.18.124.193:80:0:tcp 0 0 0 172.18.124.193:53:0:udp 0 0 0 172.18.124.192:53:0:udp 0 0 0 Virtual Machine(s) Bytes Packets Connections 172.18.124.208:80:0:tcp 0 0 0 172.18.124.208:0:0:udp 0 0 0
The show configuration command displays the current running configuration on the LocalDirector.
The syslog console and syslog output 23.7 or 20.7 commands show the results of a server failing.
<187> May 22 14:52:26 LD-ERR Real machine '172.18.124.192:53:0:udp': edited from In service to Failed (External) -- Probe. <186> May 22 14:52:32 LD-CRIT Switching '172.18.124.208:0:0:udp' from 'slowstart' to 'leastconns'
The show real command is described earlier in this document. These are the results of the show real command when DNS probe fails:
LDIR-416# show real Real Machines No Answer TCP Reset DataIn Machine Connect State Thresh Reassigns Reassigns Conns 172.18.124.192:80:0:tcp 0 IS 8 0 0 0 172.18.124.193:80:0:tcp 0 IS 8 0 0 0 172.18.124.193:53:0:udp 20 IS 8 0 0 0 172.18.124.192:53:0:udp 0 EFAILED 8 0 0 0
The show connection command verifies the current connections.
You can also use these commands to troubleshoot the configuration:
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Refer to Cisco Technical Tips Conventions for information on conventions used in this document.