wan static/dynamic ip ?

Discussion in 'Computing and Networks' started by Mathematics!, Sep 16, 2011.

  1. Mathematics!

    Thread Starter Senior Member

    Jul 21, 2008
    I am wondering if given a wan ip address at random if their is away to determine if it is a static or dynamically assigned ip address.
    I.E if the wan ip address is assigned dynamically thru a dhcp server?

    I know if it was a local address I could track down the dhcp server for that particular domain and then just look on the dhcp server to see if the ip fell into the range of dhcp pool of address assigned by the dhcp server.
    If it did then it was a dynamic ip if not then it must be static.

    But with a random wan address I don't know if their is way to do it.
    Curious though.

    For example
    suppose you had been given a wan ip address that you tracked down to be from an isp provider such as comcast, crocker, charter ,...etc is their away to find out if this ip address has a fixed destinition or if it was given to a wan computer dynamically for a certain lease time and their for may not be useable to get back to that exact computer again in the future.
    Last edited: Sep 16, 2011
  2. coligny

    New Member

    Apr 17, 2011
    >> I am wondering if given a wan ip address at random if their is away to determine if it is a static or dynamically...

    If you mean remotely... by a mean stated in a rfc, not that i know of.

    Now quite often DHCP pools from provider have a reverse DNS name like



  3. Mathematics!

    Thread Starter Senior Member

    Jul 21, 2008
    yes I mean given given an random wan ip can you determine from where you are remotely if it is static or dynamically assigned.

    Ok even if you new the ip or domain names for the dhcp servers associate with the company that owned the wan ip address is their any way to know what the range of ip address's the dhcp servers can give out?
    If you had away of getting this range then it would be just a matter of seeing if the wan ip fell into one of these ranges.

    What I can do is with whois find a companies associated net range , location, contact info ,....etc
    using nslookup I can find the dns servers associated to the companies.
    if I am lucky I can do a zone transfer using dig on all the domains and subdomains.
    After that I can look for the dhcp servers by port scanning and other means.
    Once I have found the dhcp servers is their any query or way of finding out what range of ip's they can assign from their pool?
  4. AlexR

    Well-Known Member

    Jan 16, 2008
    No, not a chance!

    The link IP addresses get allocated during the PPP link set-up so to have access you would need a valid user-name and password registered with the ISP.
    You can use WHOIS to find out the name and address of the ISP that owns the IP address then contact them and ask whether the address you are interested in is static or dynamic.
    You can be 100% sure that the DHCP server will be behind a very strong firewall and outsiders will have no access to it. All IP addresses will be allocated through PPP.
  5. Mathematics!

    Thread Starter Senior Member

    Jul 21, 2008
    Ok, thank you

    I am wondering if their was a packet/query that would let you query a dhcp server for the ip range that the dhcp server uses to assign dynamic ip's.

    For instance (for getting about security for a second) is their any way to get this info by not logging into the router/switch and looking the info up.

    Simple example
    If I am on my home network my linksys does the dhcp assigning by default.
    I can go to the page , login , and look at where the pool of dynamic address start and end (as well as modify it)

    I am wondering is their someway you can access this dhcp info with a query at the black screen. I am think like dns servers you can use nslookup to get the domain name or ip address, mx records ,...etc

    I was wondering if their was any packets/querys I could send to port 67 (dhcp service port) that would allow me to find info like I can do with dns.
    Or is the only things dhcp server's allowed to transmit is dhcp discover , dhcp request ,...etc packets. And their is no other info that dhcp server service gives out other then handing out ip , subnet , gateway , and dns server locations.

    If it is just handing out these and no other info then I would think you have to physically be inside the router/switch settings page. Or logged into the dhcp server with enough rights to view this data if it is a dedicated dhcp computer.

    Correct me if I am wrong
  6. AlexR

    Well-Known Member

    Jan 16, 2008
    Forget about dhcp, dhcp is not involved. The mechanism that allocates the IP addresses to the links is PPP in conjunction with whatever authentication server protocol the ISP uses.
    Whether the PPP allocates dynamic addresses from a pool or static addresses on a per user basis is determined by how it is set up and before you ask, NO there is no way you can remotely find out unless you have administrator login rights on the PPP router.
  7. BillO

    Distinguished Member

    Nov 24, 2008
    In addition to what Alex said, the PPP assigned address may just be the base address for a subnet of which you will have, nor be able to gain, any knowledge. These subnets may have their own DHCP servers and will most likely be behind a state-full inspection firewall as well as NAT. AFAIK, there is no way to get any meaningful information about such a structure, let alone circumvent it.

    Just curiosity, what site are you trying to crack?