1 Reply Latest reply on Oct 18, 2010 4:09 PM by Dude!

    3 IP resolving to one host via DNS

    755171
      Hi,

      For my Oracle 11gR2 RAC DB SCAN listner setup, My Network admin has setup the SCAN name in DNS to resolve to 3 IPS. (OS : Red-hat Linux 5, 64 bit machine)

      When I do "ping <scan_name>", then it resolves to one of the 3 IPs in round-robin fashion.
      But, it sends a proper response back only for 1 IP.
      For other 2 IPs, it resolves to the correct IP, but it says "Destination Host Unreachable".
      Here is the example : (Pls. notice that, I get proper response only for 10.1.96.76)

      [grid@P01STORA001 bin]$ ping P01STRAC-SCAN
      PING P01STRAC-SCAN.test01.in (10.1.96.77) 56(84) bytes of data.
      From P01STORA001.test01.in (10.1.96.66) icmp_seq=2 Destination Host Unreachable
      From P01STORA001.test01.in (10.1.96.66) icmp_seq=3 Destination Host Unreachable
      From P01STORA001.test01.in (10.1.96.66) icmp_seq=4 Destination Host Unreachable

      --- P01STRAC-SCAN.test01.in ping statistics ---
      4 packets transmitted, 0 received, +3 errors, 100% packet loss, time 2999ms
      , pipe 3
      [grid@P01STORA001 bin]$
      [grid@P01STORA001 bin]$ ping P01STRAC-SCAN
      PING P01STRAC-SCAN.test01.in (10.1.96.76) 56(84) bytes of data.
      64 bytes from P01STRAC-SCAN.test01.in (10.1.96.76): icmp_seq=1 ttl=64 time=0.015 ms
      64 bytes from P01STRAC-SCAN.test01.in (10.1.96.76): icmp_seq=2 ttl=64 time=0.019 ms

      --- P01STRAC-SCAN.test01.in ping statistics ---
      2 packets transmitted, 2 received, 0% packet loss, time 1001ms
      rtt min/avg/max/mdev = 0.015/0.017/0.019/0.002 ms
      [grid@P01STORA001 bin]$ ping P01STRAC-SCAN
      PING P01STRAC-SCAN.test01.in (10.1.96.78) 56(84) bytes of data.
      From P01STORA001.test01.in (10.1.96.66) icmp_seq=2 Destination Host Unreachable
      From P01STORA001.test01.in (10.1.96.66) icmp_seq=3 Destination Host Unreachable
      From P01STORA001.test01.in (10.1.96.66) icmp_seq=4 Destination Host Unreachable

      --- P01STRAC-SCAN.test01.in ping statistics ---
      4 packets transmitted, 0 received, +3 errors, 100% packet loss, time 3000ms
      , pipe 3

      As per my network administrator, this DNS is set up with statis IPs and this behavior
      is normal with a statis DNS setup.

      Any help please? How to get proper response from all the 3 IPs?

      Your help is very much appreciated !!
        • 1. Re: 3 IP resolving to one host via DNS
          Dude!
          Without knowing what you are trying to achieve it will be difficult to suggest a solution. If I understand your setup correctly, your admin has added your computer to a DNS server that provides 3 name resolutions in a round robin fashion. The reason to setup a DNS round-robin is usually to have subsequent client connections directed to different computers. For this to work, the TTL (time to live) value of a DNS rercord also need to be set to a very short time. DNS does however not not care if the destination host or IP is not online. DNS resolving will be done first using the local /etc/hosts file of the computer before using the specified DNS server. You may want to check your /etc/hosts file to make sure it is set accordingly. DNS round-robin on a local machine to itself however does not make much sense. Also, /etc/hosts file does not provide a round-robin feature and just uses the first matching entry it finds.

          Edited by: waldorfm on Oct 18, 2010 8:59 AM