dynamic dns

Discussion in 'Cisco' started by ra5467, Jul 7, 2003.

  1. ra5467

    ra5467 Guest

    can anyone give me a good, detailed explanation of how these dynamic
    dns update programs work? my router/firewall is connected to the isp
    with a dynamic ip. i would like to write something to update my ip
    myself. these 3d party sites have ddns update programs that reside on
    client machines, but you have to register with their site and use them
    as the dns host. i'm guessing they're using nslookup to do some kind
    of reverse lookup every so often, but i'm not sure.

    thx

    p.s. is it true that newer versions of bind have some ddns capability
    built in and what does this mean?
     
    ra5467, Jul 7, 2003
    #1
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  2. :can anyone give me a good, detailed explanation of how these dynamic
    :dns update programs work? my router/firewall is connected to the isp
    :with a dynamic ip. i would like to write something to update my ip
    :myself. these 3d party sites have ddns update programs that reside on
    :client machines, but you have to register with their site and use them
    :as the dns host. i'm guessing they're using nslookup to do some kind
    :eek:f reverse lookup every so often, but i'm not sure.

    You do not need reverse DNS for this task.

    You run a program on a client machine that contacts a daemon at
    the provider and logs in with the username and password. The
    daemon looks at the IP address the connection was made from and
    looks up the last-registered IP address for the account in a
    database. If the connection IP address is different than the
    last registered one, then the daemon updates the database and
    updates the DNS tables.


    :p.s. is it true that newer versions of bind have some ddns capability
    :built in and what does this mean?

    I am not sure, but I believe this refers to to dynamic DNS as
    practiced by Windows boxes; these days when Windows boxes are
    assigned addresses via DHCP, they attempt to send an address update
    to their DNS server.
     
    Walter Roberson, Jul 7, 2003
    #2
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  3. ra5467

    Rod Dorman Guest

    Does anyone know what range of TTL's they tend to report?

    Seems to me in order to be responsive to the whims of DHCP assignments
    that they'd have to use a low TTL, but, that will defeat the benefits
    of cacheing and increase the DNS bandwith requirements & server loads
    of the rest of the world.
     
    Rod Dorman, Jul 7, 2003
    #3
  4. [with regards to dynamic dns servers]

    :Does anyone know what range of TTL's they tend to report?

    :Seems to me in order to be responsive to the whims of DHCP assignments
    :that they'd have to use a low TTL, but, that will defeat the benefits
    :eek:f cacheing and increase the DNS bandwith requirements & server loads
    :eek:f the rest of the world.

    The figure I've seen most often [in my limited experience] has been
    one hour.

    Hosts that rely on dynamic DNS tend not to be in high demand as
    lookup targets, it seems to me.
     
    Walter Roberson, Jul 7, 2003
    #4
  5. :i was trying to figure out a solution for
    :my own personal use. i'm trying to get some feedback on whether this
    :would work. what i would like to do is figure out a way to contact my
    :isp's dhcp (dhcp-type, cable networks are set up a bit differently)
    :server. i would then like to do a rarp on my router's mac address and
    :hopefully retrieve the current ip. if i could script all this, i
    :could then use the, i think it's "nsupdate" command, to propogate that
    :information back out.

    Does your ISP's box or first-hop allow you to SNMP to it? If so then you
    could walk the SNMP
    ip.ipNetToMediaTable.ipNetToMediaEntry.ipNetToMediaPhysAddress
    table. Match the MAC address on the result, peal off the last four
    octets of the OID, and that's the IP address.

    If, though, you do not control the first hop device, then I would think
    it unlikely that you could get the access you were thinking of.
    For one thing, rarp is not a commonly supported protocol.
     
    Walter Roberson, Jul 17, 2003
    #5
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