Static IP Addresses

Posted on 2004-10-22
Last Modified: 2011-05-19
Can the same static IP address be assigned to more than one service on the same server? If so, how are conflicts avoided. I was under the impression that each device/host/service needs its own static IP address in order to communicate. I appreciate that workstations can be configured to request IP addresses from the DHCP server, but I'm referring to other devices/services.

Question by:Peter_Fabri
    LVL 20

    Expert Comment

    If the server already has a static IP address, every service on that service is already referenced by that static IP address. The services conflicts are avoided by the use of "virtual" ports. In other words, FTP typically uses port 21. So if your server has the FTP service running, I could connect to it with an FTP client using the address (notice my reference to the port to tell the application I want to access the service listening on port 21)
    LVL 5

    Assisted Solution

    If you mean can a server have both FTP and HTTP services running for the same IP address, yes you can.  There aren't conflicts because the services have different port numbers.  If you mean you have 2 print servers with the same IP address, you're going to have problems with those until you can change an IP or put in a switch/router that can isolate them from each other but communitcate to both of them.
    LVL 6

    Expert Comment

    Not quite sure what you are asking here...maybe an explanation of what you are trying to do would help...

    As to what I have read...

    The Static IP addres is assigned to the Manchine (or Host).  The services (HTTP, SMTP, TELNET, RDP, POP, etc...) are assigned to ports that are attached to the IP HTTP uses port 80, TELNET uses port 23

    If a machine had multiple network cards...each card would need to have its own IP address
    LVL 6

    Expert Comment

    Whoops...too slow
    LVL 3

    Assisted Solution

    Well there are times which protocols like HSRP / VRRP that 2 devices like routers / firewalls share one IP and MAC address for load balancing or redundancy purposes.
    Otherwise yes IP addresses must be unique.  Kinda like your house number mailman can't deliver your mail if 2 houses on your street have the same address. You might get some of your mail the other person might get the other half etc.

    -= Felix =-

    Author Comment

    At work we have a voice mail service and a service for the swipe card systems for staff. Both services residing on the same stand alone pc, which is acting as a server for these services. I was asked if the same static IP address could be used for the voice mail bedore activating it. It appears it can as there was no conflict, but I am not sure if ports are involved. Maybe this works much in the same way as the DNS/DHCP server having the same IP address as my server!

    Any comments/clarification is much appreciated.

    LVL 3

    Accepted Solution

    Yes those services probably run on 2 difference ports.  No two applications can use the same port on the same ip.  Think of ports like and extention to a phone number.

    So if we look at maybe an all round server for example
    It could run
    FTP on port 21
    DNS on 53
    DHCP (67/68)
    Webserver on 80
    POP3 Mail on 110

    So all these could be "connected" to one IP.  You could not however run say FTP and Webserver both on port 80.

    -= Felix =-


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