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Cisco LocalDirector 400 Series

How to Configure a DNS Probe on LocalDirector

Document ID: 12618

Updated: Jan 31, 2006

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Introduction

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.

Prerequisites

Requirements

There are no specific requirements for this document.

Components Used

The information in this document is based on these software and hardware versions:

  • LocalDirector 416

  • 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.

Conventions

Refer to Cisco Technical Tips Conventions for more information on document conventions.

Network Diagram

This document uses this network setup:

dns_probe_ld.gif

How to Configure a DNS Probe on LocalDirector

Use these steps to configure the LocalDirector:

  1. Configure all ports for a virtual User Datagram Protocol (UDP).

    virtual 172.18.124.208:0:0:udp is
    
  2. 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
    
  3. 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
    
  4. 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
    

Verify the Configuration

Use this section to confirm that your configuration works properly.

The Output Interpreter Tool (registered customers only) (OIT) supports certain show commands. Use the OIT to view an analysis of show command output.

show version

The show version command displays the software version that is running on the LocalDirector.

LDIR-416# show version

LocalDirector 416 Version 4.2.1

show running-config

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 64.0.0.0 255.0.0.0

  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

show bind

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)

show virtual

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

show real

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

show statistics

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

show configuration

The show configuration command displays the current running configuration on the LocalDirector.

Troubleshoot the Configuration

The Output Interpreter Tool (registered customers only) (OIT) supports certain show commands. Use the OIT to view an analysis of show command output.

syslog console and syslog output

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'

show real

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

show connection

The show connection command verifies the current connections.

Other show Commands

You can also use these commands to troubleshoot the configuration:

Related Information

Updated: Jan 31, 2006
Document ID: 12618