DNS Round Robin

[Masataka_Tanaka]

# Prompt reply is very very welcome q(^o^)p

Hello, there.

My current BIND working environment is under Solaris 2.6 and BIND 8.x .
I would like to ask you all the question about DNS round robin.
When we set several hosts as Round Robin, do they have fail-safe
function or not?

I shall tell you about my basic trials.

Case1 - DNS Setup

1)  First, I set up two hosts as having same name and different IP.
    They named Robin.domainname in FQDN.(y.y.y.0/24 segment)

    # nslookup
    > Robin.domainname
    Name:    Robin.domainname
    Addresses:  y.y.y.95, y.y.y.109


    > y.y.y.95
    Name:    Robin.domainname
    Address:  x.x.x.95

    > y.y.y.109
    Name:    Robin.domainname
    Address:  y.y.y.109


2)  Send the ICMP packets from some nameserver via 'ping' command.
     ( Network Layer; OSI layer 3)
      itcns2# ping mail.uhclan.sony.co.jp
      ICMP Host redirect from gateway (x.x.x.254) to x.x.x.247 for y.y.y.95
      Robin.domainname is alive

       On this host, Name Service Cache Daemon (nscd) works, and looks
       Cached result is quoted for next DNS lookup.(within the range of TTL)

# Q1.    When 'nscd' process stopped at working DNS server, does it
           influent for named service or some cache??


       When I stop one of the hosts in Round Robin and type 'ping', I got
the
       result shown as below.

       [ Alive Host ]

       nameserver# ping Robin.domainname
       ICMP Host redirect from gateway (x.x.x.254) to x.x.x.247 for
y.y.y.109
       Robin.domainname is alive

       [ Dead Host ]

       nameserver# ping y.y.y.95
       ICMP Host redirect from gateway (x.x.x.254) to x.x.x.247 for y.y.y.95
       no answer from y.y.y.95

On network layer level, it looks fail-safe works due to ROund Robin setup.



Case2 - Shutdown one of hosts during ICMP packets transmit, and check
            fail safe via DNS Round Robin Configuration

1. Type the 'ping' command.

    nameserver# ping -s [ RoundRobin_HOST FQDN ]


2. ICMP packet trasnsmitted regularly, and one of hosts replyed.

    ICMP Host redirect from gateway (x.x.x.254) to x.x.x.247 for y.y.y.109
    64 bytes from y.y.y.109: icmp_seq=0. time=3. ms
    64 bytes from y.y.y.109: icmp_seq=32. time=2. ms
    . . . . . . . .
    64 bytes from y.y.y.109: icmp_seq=42. time=2. ms


3. Shutdown the alive host.

    ICMP Host redirect from gateway (x.x.x.254) to x.x.x.247 for y.y.y.109


4. Interrupt ICMP transmission because I confirmed host doesn't
   reply anymore.

   ----mail.uhclan.sony.co.jp PING Statistics----
   107 packets transmitted, 43 packets received, 59% packet loss
   round-trip (ms)  min/avg/max = 2/3/12


# Q2.    Is there any way to realize fail-safe(switch-over) via DNS
configuration?
           ( I mean the definition of 'fail-safe' :
              One of Round Robin hosts is dead, avoiding DNS lookup returns
the Dead
              host information.)

            Ohterwise, is there any SOFTWARE tool monitoring hosts or ports
of DNS hosts?
            (if possible freeware)

I am looking forward to getting your reply soon.
Bye for now, and thank you so much for reading to the last.

--
Thanks & Have a good day !
Sony Systems Design Corp.
Customer Service Dept.
Masataka TANAKA
mail to :  mtanaka at ssd.sony.co.jp
tel       :  +81-3-5479-6629 (Tokyo, Japan)