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Gateway Address Changes on its own

By wazza
Mar 19, 2007
  1. Hi All

    My gateway IP address of my network card changes all by itself.

    I set the NICs IP info manually.

    This is what it looks like

    IP address : 172.31.1.241
    Subnet : 255.255.255.0
    Gateway : 172.31.1.254

    The gateway IP changes to 172.31.1.252 or it changes to nothing(empty field) all on it own, no intervention.

    What the hell is going on?

    The PC is Windows XP SP2 and is connected to a Cisco 3750 switch.

    Help!
     
  2. Nodsu

    Nodsu TS Rookie Posts: 5,837   +6

    Well, needs to find out what changes it..

    Stop and disable the DHCP client service for starters. Do you have any software installed that stores network profiles for you or something else like VPN software or some "security" suite that "protects" your settings?
     
  3. jobeard

    jobeard TS Ambassador Posts: 9,343   +622

    it's most likely a DHCP change from the router --

    BUT WHY are you trying to manually set the IP environment?
    It's a rare environment that requires a manual config (eg a server).

    Give in and let DHCP do it's thing ;)
     
  4. wazza

    wazza TS Rookie Topic Starter Posts: 69

    I am running Comodo Firewall on my Server.

    I have to configure my IP settings as I have setup a NAT so that the server is available on the Internet.
     
  5. jobeard

    jobeard TS Ambassador Posts: 9,343   +622

    1) config your Server to have a STATIC IP address
    2) config Comodo to port forward the server ports to that STATIC ip

    It is possible on some routers to still use DHCP + MAC filtering to force
    a continuous assignment of the same IP address -- the benefit being
    DHCP still provides the gateway and DNS settings.
     
  6. wazza

    wazza TS Rookie Topic Starter Posts: 69

    1) my server is configured to have a static IP address
    2) done

    Thanks 4 the help, will monitor now, to see if it triees to change the Gateway again. I am reading into MAC filtering

    Thanks asgain
     
  7. mikescorpio81

    mikescorpio81 TS Rookie Posts: 293

    One other thing ...

    A Class B IP range (172.x.x.x) requires a 255.255.0.0 subnet mask.
    You can get away with it when it's Microsoft, but not with Linux/Unix/etc.

    There is no real point in using a subnet like that if you aren't going to have more than 253 PC's within your LAN. Stick to a Class C (192.168.x.x) range :grinthumb
     
  8. Nodsu

    Nodsu TS Rookie Posts: 5,837   +6

    Uhm, network classes are ancient history - we have CIDR now. And besides, you can do anything you like on your private network. And the "official" network mask for a B network is 12 bits (which translates to 255.240.0.0).
     
  9. jobeard

    jobeard TS Ambassador Posts: 9,343   +622

    and any subnet, regardless of class a,b,c can have a more restrictive
    mask 255.255.255.0 -- heck -- even 255.255.255.255 is legit!
     
  10. mikescorpio81

    mikescorpio81 TS Rookie Posts: 293

    For Microsoft-based systems; yes ... but try and give a Class B IP address a Class C subnet on RedHat or even a Unix-based Mac and see what happens.

    I was only pointing out the fact that the correct subnets should be used because non Microsoft-based networks will not comply. CIDR increases the amount of clients over Class IP addressing, but what is the point for a simple home network? I think most home users and businesses for that matter require less than 1000+ IP addresses and even if you do require more, use a class A 10.x.x.x range with a 255.0.0.0 subnet.
     
  11. Nodsu

    Nodsu TS Rookie Posts: 5,837   +6

    Uhm. I just did that. Nothing happened. Well, besides the fact that since the router has a different netmask, my internet connection broke. But that has nothing to do with network classes.

    Do you actually have any idea what you are talking about?
     
  12. jobeard

    jobeard TS Ambassador Posts: 9,343   +622

    Networking has to do with routers and NIC cards, NOT
    the OS system(s) to which they are attached. The sole caveat here is the
    routing table which can be mucked over by anyone with root/admin access.
    There are cheap (ie low quality/function) routers that most home users have access to
    which limit the settings in a parochial manner, but I.T. infrastructure equipment
    will not do so and allow A KNOWLEGABLE person to set whatever he/she desires --
    all with the intent of creating custom networks.
     
  13. mikescorpio81

    mikescorpio81 TS Rookie Posts: 293

    Recently I built a Redhat proxy server within a Microsoft network. Their network LAN addressing was 10.x.x.x - 255.255.255.0. While I was trying to give the proxy it's IP address with that subnet, it would automatically revert the subnet to 255.0.0.0, not once letting me submit the class c subnet.

    Solution? I had to re-address the entire network. It took me 3hrs all up with testing, and I had the blessing from my bosses who both have 20+ years of networking experience. If there was another way to do this by all means please tell me as I'd love to know for future reference.

    BTW I am MCSE and CCNA qualified and have been an I.T Technician now for 3 years. Please don't assume I am an *****! My post was only to point out this kind of problem that I experienced, for you see, if you don't experience the problem, how do you know it can or can't happen?

    You can't just brush off Class IP ranges. It is still being taught to MCSE wanna-be students as it is important to understand.

    I take it when you tried what I suggested you tried to add a Redhat or Linux based OS into your network that is obviously miss-matched (EG: 172.16.x.x - 255.255.255.0)?
     
  14. jobeard

    jobeard TS Ambassador Posts: 9,343   +622

    I kindly suggest you had other problems and just acquiesced into the easiest
    solution under the pressure of the day. ANYTIME, your setting change and
    you can't answer why -- there's clearly something to be investigated.

    btw: I've been doing this for 37+ years -- so much for your single one-time experiences.

    go back to your MSCE and CNAA notes: any class a,b,c address can be
    served by a subnet mask of 255.255.255.0 or even more tightly by 255.255.255.255

    Now I suggest we quite playing king-of-the-mountain and get back to helping
    the users; I'll not join you in this game any further :)

    Best Wishes, Jeff
     
  15. mikescorpio81

    mikescorpio81 TS Rookie Posts: 293

    Sorry to offend, it was not my intention but to be honest I felt somewhat offended! :(
    I experienced the above problem and thought I'd share it with you all. Next time I'll shut my mouth ...
     
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