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Can't open a website/ping a host from certain subnet, other subnets on same network can

By SoulSeeker
Sep 16, 2016
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  1. Hi
    I have a networking problem at work that is bugging me, hopefully someone can give me a push in the right direction.

    From subnet A, I can ping my server at home and access my server via https.
    From subnet B, I can't ping my server and I can't open the https page, although the DNS resolves the IP correctly. Same if I ping the IP directly. This is true for all clients in that subnet, including the DHCP-Server. Other sites/IPs I tried are fine, it is just this particular one (as far as I know, there could be many more that don't work though).

    I'm almost sure it's something with the DHCP-Server, but the configuration is, as far as I can tell, identical for the DHCP-Servers in both subnets, appart from the obvious difference of serving a different subnet.

    Any ideas where I need to look for a solution?
     
  2. jobeard

    jobeard TS Ambassador Posts: 9,322   +622

    Sounds like you have two routers chained together, something like
    ISP==router#1---router#2
    subA . . . . subB​

    Let's be clear on the logistics:
    1. you are outside your system, say like at work
    2. you can ping a subnet A at home
    3. but can not ping subnet B at home
     
  3. SoulSeeker

    SoulSeeker TS Rookie Topic Starter Posts: 17

    I'll try to explain better:

    1. I'm indeed at work. At work, there are actually 5 subnets I have access to, plus more I don't have access to. I only stated A and B, but C, D and E can also ping my server at home.
    2. I can ping my home server from work subnet A (and, to be precise, also from C,D and E)
    3. But I can't ping my home server from work subnet B. All other pinged sites respond just fine.

    I have access to the DHCP-Servers of Subnets A-E and they are configured the same. I don't have access to the routers and the core switches, but they should be the same for all as well.

    What could explain a route not being found from subnet B to my home, even though all other subnets, nested in the same network, have no problem?
     
  4. jobeard

    jobeard TS Ambassador Posts: 9,322   +622

    OK, this can be fun :)
    First issue is the site configuration and default routing(s). There are two common layouts:
    The last one is most typical. The issue is your Router B - - what services are on that subnet, any internal business systems? It is typical for some subnets to be denied Internet access.

    For A,C,..Z, the default route will be to the primary.router which then has access to the internet.
     
  5. SoulSeeker

    SoulSeeker TS Rookie Topic Starter Posts: 17

    Thanks for the reply. I found the reason, why only subnet B is not able to reach my server at home. :confused: Actually my doing.

    A while ago I configured my router at home to automatically use a VPN tunnel for connections to this particular subnet, so I can reach my work servers from home. I completely forgot I set this up (shows how well it has been working). Seems being send on a detour on their way back is to confusing for those little TCP/IP packets. ;)

    Sorry I wasted your time
     

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