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Question on basic route table on home PC

Discussion in 'Network Infrastructure' started by mjtibbs, Oct 2, 2007.

  1. mjtibbs

    mjtibbs Bit Poster


    Basically the setup is this,

    -1 BT Voyager eth/usb 2port router/modem
    -1 pc connected via ethernet, IP is
    -1 pc connect via usb, IP

    from the 168.1.3 box I can sucessfuly ping 168.1.4.

    however, I type the "route print" command on the 1.3 box and I do not see an entry that shows how this is routed.

    I "red-boxed" the closest entry I see, however it would appear to use the same NIC as the next hop?? in that case,how would it ever make contact with the router (168.1.1).

    If this is correct, then does it just fall back on the default route to make contact with the router, to then ping the box connected via USB.

    I attached a couple screens, one of the routeprint cmd on the 168.1.3 box, and also the tracert result on the same box, which shows it definatly making contact with the router.

    Thanks if anyone can clear this up.. its bugging the hell out of me and I want to fully understand routing tables.

    Certifications: MCSA, OSCP, MCTS Config SharePoint 2007
  2. BosonMichael
    Highly Decorated Member Award

    BosonMichael Yottabyte Poster

    374 is on the local network, so packets going there do not need to be routed. The only reason you see the router on a trace is because you're passing your data through it. If you were tracing through a switch or a hub, it would look as if it were going directly to 1.4.

    Your routing table basically says that all packets destined for the network will go out your NIC. So that's what it's doing. The device connected to the other end of the cable is your router, and since it's a Layer 3 device, it can respond back with it's IP when you trace it out. Your router knows where 1.4 is, and sends the packets there.
    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!
  3. nicolinux

    nicolinux Byte Poster

    If i understand well the lan interface and the usb interface are bridged.
    This is done so both can share the some gateway.
    Certifications: mcse win2k3, mcts x4. mcitp enterprise admin
    WIP: 70-680
  4. mjtibbs

    mjtibbs Bit Poster

    Hi guys,

    thanks for the info , thats cleared that up.

    I was reading the route table entry as if it would route the packets back INTO the NIC, thinking it would create a sort of loop, thus couldn't understand how the packets were getting out to the router, but I understand now that its actually routing the packets OUT of the nic into the device connected (my router).

    So on that basis, If all packets will be sent out of my NIC into the router regardless, then I thought I would change some of the TCP/IP settings for my NIC just to see the outcome.

    I changed the nics tcp/ip default gateway from to (same IP as my NIC) with the idea that the packets will go out of my NIC, to the router, which the router will when then use its own route table and determine that if any routes were destined to foreign networks.. it would route them out to my first ISP's router (as is the default route on my routers route table).

    I also changed the preferred DNS server to the same IP as my NIC. (altthough I done the testing using IPs anyway because I only wanted to test connectivity first)

    Well, this didnt work, and I lost all connectivty to forgeign networks (flushed my dns etc before hand to test).

    However, I could still ping the other box downstairs, (mentioned in my first post).

    How come this is the case, that I couldn't connect to other websites etc, when I used the default gateway of my NIC, thinking that that the packets would still arrive at my router, and my router when then forward them on as required. I done a tracert on a few foreign IP's and I noticed that my NIC was not sending anything through my 1.1 router at all.

    I have set the default gateway/pref dns server back to 1.1 and all is fine again.

    Thanks for the help btw, its much appreaciated... If I dont get a grip on my little BT Voyager/DSL connection... what hope do I have of bull riding an organisations infrastructure (thats my theory anyway lol)
    Certifications: MCSA, OSCP, MCTS Config SharePoint 2007

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