Routing question

Discussion in 'Networks' started by Eatskittens, Feb 17, 2010.

  1. Eatskittens

    Eatskittens New Member

    2
    0
    11
    I have a question. If there are 2 networks connected by router. And on one network a host is configured with an incorrect GW can hosts from the other network communicate with it? If not could you tell me why?
     
    Certifications: A+
  2. soundian

    soundian Gigabyte Poster

    1,460
    71
    107
    That's got me thinking.
    If the host (Host A) with the incorrectly configured GW is on the same subnet as the GW, then the other host (host B) should be able to send it packets. Host A should then return them to the actual GW, because as far as it knows, that's where they originated.
    However, if host A tries to initiate contact with host B, the router will ignore the packets because they aren't addressed to it.
    So, if I'm right, they can communicate only if host B intitiates the connection.


    Now I'm gonna run for cover as the experienced guys tear holes in my logic.
     
    Certifications: A+, N+,MCDST,MCTS(680), MCP(270, 271, 272), ITILv3F, CCENT
    WIP: Knuckling down at my new job
  3. BosonMichael
    Honorary Member Highly Decorated Member Award 500 Likes Award

    BosonMichael Yottabyte Poster

    19,183
    500
    414
    If there's no route, there's no way to get to the destination.
     
    Certifications: CISSP, MCSE+I, MCSE: Security, MCSE: Messaging, MCDST, MCDBA, MCTS, OCP, CCNP, CCDP, CCNA Security, CCNA Voice, CNE, SCSA, Security+, Linux+, Server+, Network+, A+
    WIP: Just about everything!
  4. SimonD
    Honorary Member

    SimonD Terabyte Poster

    3,681
    440
    199
    As Michael said, with no route out from the host it won't go outside of it's own network segment.
    That's the idea of the 'GATEWAY', it's a gateway to other places.

    What will happen is that if the machine with the correct gw address pings, it won't actually receive any replies back so will get a non reply (rather than host unreachable, it will be like ICMP packets have been dropped at a firewall.

    If the host that has the incorrect gw configured tries to ping he should get a destination host unreachable message because all it knows about is it's local subnet and it has no way to go beyond it's own boundaries.

    That's the logic behind tracert or pathping, it can tell you to a certain degree where packets are being dropped.
     
    Certifications: CNA | CNE | CCNA | MCP | MCP+I | MCSE NT4 | MCSA 2003 | Security+ | MCSA:S 2003 | MCSE:S 2003 | MCTS:SCCM 2007 | MCTS:Win 7 | MCITP:EDA7 | MCITP:SA | MCITP:EA | MCTS:Hyper-V | VCP 4 | ITIL v3 Foundation | VCP 5 DCV | VCP 5 Cloud | VCP6 NV | VCP6 DCV | VCAP 5.5 DCA
  5. Sparky
    Highly Decorated Member Award 500 Likes Award

    Sparky Zettabyte Poster Moderator

    10,718
    543
    364
    No, because the traffic will not be able to route back the way to the original host that made the request.
     
    Certifications: MSc MCSE MCSA:M MCSA:S MCITP:EA MCTS(x5) MS-900 AZ-900 Security+ Network+ A+
    WIP: Microsoft Certs
  6. beaumontdvd

    beaumontdvd Kilobyte Poster

    487
    3
    32
    That has helped me understand about gateways I didn't know any of that. thanks mate, worded it perfect.

    Reppped :biggrin

    Dave
     
    Certifications: 070-271, 070-272, (MCDST)Level 1,2,3 NVQ
    WIP: 070-270, A+, N+, S+,MCDST 7 Upgrade
  7. danielno8

    danielno8 Gigabyte Poster

    1,306
    49
    92

    just to clarify, the packet host A recieved will be addressed with a source IP of host B (which is on a different subnet). As it is on a different subnet, it will send to the incorrect GW and fail to reach host B.
     
    Certifications: CCENT, CCNA
    WIP: CCNP

Share This Page

Loading...
  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.