ip_forwarding / gateway - Networking

This is a discussion on ip_forwarding / gateway - Networking ; Hello, I am building a network of Linux boxes running a small self-made Linux. One of these boxes is setup as a dial-in server for the network. I have the dial-in part up and running, but have difficulties configuring the ...

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Thread: ip_forwarding / gateway

  1. ip_forwarding / gateway

    Hello,

    I am building a network of Linux boxes running a small self-made Linux. One
    of these boxes is setup as a dial-in server for the network. I have the
    dial-in part up and running, but have difficulties configuring the network
    such that I can reach the Linux boxes from out of the network.

    This is my setup:

    92.168.2.1 <---ppp---> 192.168.2.2 <---ip_forwarding on the dial-in
    server---> 192.168.5.1 <--- eth ---> 192.168.5.2 <--- eth ---> 192.168.5.3
    etc.

    My dial-in server has ip address 192.168.2.2 on the ppp connection and
    192.168.5.1 on the eth connection. 192.168.5.x is the Linux network.
    Ip_forwarding is turned on the dial-in server.

    Using the pc with IP address 192.168.2.1, I am able to ping the Linux
    dial-in server on both its IP addresses (192.168.2.2 and 192.168.5.1).
    However, I cannot reach the Linux boxes with IP addresses 192.168.5.2 and
    up. When I ping these boxes, I can see the lights of the Ethernet cards
    flicker, but the ping requests time out.

    Am I overlooking something? Any help is greatly appreciated.

    Regards,
    Whinyan.



  2. Re: ip_forwarding / gateway

    Hello,

    Whinyan a écrit :
    >
    > 92.168.2.1 <---ppp---> 192.168.2.2 <---ip_forwarding on the dial-in
    > server---> 192.168.5.1 <--- eth ---> 192.168.5.2 <--- eth ---> 192.168.5.3
    > etc.
    >
    > My dial-in server has ip address 192.168.2.2 on the ppp connection and
    > 192.168.5.1 on the eth connection. 192.168.5.x is the Linux network.
    > Ip_forwarding is turned on the dial-in server.
    >
    > Using the pc with IP address 192.168.2.1, I am able to ping the Linux
    > dial-in server on both its IP addresses (192.168.2.2 and 192.168.5.1).
    > However, I cannot reach the Linux boxes with IP addresses 192.168.5.2 and
    > up. When I ping these boxes, I can see the lights of the Ethernet cards
    > flicker, but the ping requests time out.


    Do the hosts in the 192.168.5.x network have a route to 192.168.2.x (or
    a default route) via gateway 192.168.5.1 ?

  3. Re: ip_forwarding / gateway

    Pascal Hambourg wrote:
    > Hello,
    >
    > Whinyan a écrit :
    >
    >>
    >> 92.168.2.1 <---ppp---> 192.168.2.2 <---ip_forwarding on the dial-in
    >> server---> 192.168.5.1 <--- eth ---> 192.168.5.2 <--- eth --->
    >> 192.168.5.3
    >> etc.
    >>
    >> My dial-in server has ip address 192.168.2.2 on the ppp connection and
    >> 192.168.5.1 on the eth connection. 192.168.5.x is the Linux network.
    >> Ip_forwarding is turned on the dial-in server.
    >>
    >> Using the pc with IP address 192.168.2.1, I am able to ping the Linux
    >> dial-in server on both its IP addresses (192.168.2.2 and 192.168.5.1).
    >> However, I cannot reach the Linux boxes with IP addresses 192.168.5.2 and
    >> up. When I ping these boxes, I can see the lights of the Ethernet cards
    >> flicker, but the ping requests time out.

    >
    >
    > Do the hosts in the 192.168.5.x network have a route to 192.168.2.x (or
    > a default route) via gateway 192.168.5.1 ?


    Yes, they do have a route to 192.168.2.x via gateway 192.168.5.1.

  4. Re: ip_forwarding / gateway

    Whinyan wrote:
    > Hello,


    > I am building a network of Linux boxes running a small self-made Linux. One
    > of these boxes is setup as a dial-in server for the network. I have the
    > dial-in part up and running, but have difficulties configuring the network
    > such that I can reach the Linux boxes from out of the network.


    > This is my setup:


    > 192.168.2.1 <---ppp---> 192.168.2.2 <---ip_forwarding on the dial-in
    > server---> 192.168.5.1 <--- eth ---> 192.168.5.2 <--- eth ---> 192.168.5.3
    > etc.


    > My dial-in server has ip address 192.168.2.2 on the ppp connection and
    > 192.168.5.1 on the eth connection. 192.168.5.x is the Linux network.
    > Ip_forwarding is turned on the dial-in server.


    > Using the pc with IP address 192.168.2.1, I am able to ping the Linux
    > dial-in server on both its IP addresses (192.168.2.2 and 192.168.5.1).
    > However, I cannot reach the Linux boxes with IP addresses 192.168.5.2 and
    > up. When I ping these boxes, I can see the lights of the Ethernet cards
    > flicker, but the ping requests time out.


    > Am I overlooking something? Any help is greatly appreciated.


    Maybe the pppd proxyarp option?

    --
    Clifford Kite

  5. Re: ip_forwarding / gateway

    Clifford Kite wrote:
    > Whinyan wrote:
    >> This is my setup:

    >
    >> 192.168.2.1 <---ppp---> 192.168.2.2 <---ip_forwarding on the dial-in
    >> server---> 192.168.5.1 <--- eth ---> 192.168.5.2 <--- eth ---> 192.168.5.3
    >> etc.

    >
    >> My dial-in server has ip address 192.168.2.2 on the ppp connection and
    >> 192.168.5.1 on the eth connection. 192.168.5.x is the Linux network.
    >> Ip_forwarding is turned on the dial-in server.

    >
    >> Using the pc with IP address 192.168.2.1, I am able to ping the Linux
    >> dial-in server on both its IP addresses (192.168.2.2 and 192.168.5.1).
    >> However, I cannot reach the Linux boxes with IP addresses 192.168.5.2 and
    >> up. When I ping these boxes, I can see the lights of the Ethernet cards
    >> flicker, but the ping requests time out.

    >
    >> Am I overlooking something? Any help is greatly appreciated.

    >
    > Maybe the pppd proxyarp option?


    Perhaps. Perhaps routing weirdness on 192.168.5.2. Perhaps both. A
    drawing that clearly labeled interfaces and hosts would be useful, along
    with the routing table on the host with the interface labeled
    192.168.5.2. An IP address is associated with an interface, not a host.
    The distinction matters when you are dealing with hosts with more than
    one interface.

  6. Re: ip_forwarding / gateway

    Allen McIntosh wrote:

    [clip]
    > An IP address is associated with an interface, not a host.
    > The distinction matters when you are dealing with hosts with more than
    > one interface.


    This is simply not true on Linux which uses the "so-called" WeakES
    model.

    The IP's most certainly do _belong_ to the the host and not the nic.
    That's why a multihomed Linux host will gladly respond to any
    assigned IP regardless on which nic it arrives.

    It can make life very exciting ;-)

    prg


  7. Re: ip_forwarding / gateway

    Whinyan writes:

    > Pascal Hambourg wrote:
    > > Hello,
    > > Whinyan a écrit :
    > >
    > >>
    > >> 92.168.2.1 <---ppp---> 192.168.2.2 <---ip_forwarding on the dial-in
    > >> server---> 192.168.5.1 <--- eth ---> 192.168.5.2 <--- eth --->
    > >> 192.168.5.3
    > >> etc.
    > >>
    > >> My dial-in server has ip address 192.168.2.2 on the ppp connection and
    > >> 192.168.5.1 on the eth connection. 192.168.5.x is the Linux network.
    > >> Ip_forwarding is turned on the dial-in server.
    > >>
    > >> Using the pc with IP address 192.168.2.1, I am able to ping the Linux
    > >> dial-in server on both its IP addresses (192.168.2.2 and 192.168.5.1).
    > >> However, I cannot reach the Linux boxes with IP addresses 192.168.5.2 and
    > >> up. When I ping these boxes, I can see the lights of the Ethernet cards
    > >> flicker, but the ping requests time out.

    > > Do the hosts in the 192.168.5.x network have a route to 192.168.2.x
    > > (or a default route) via gateway 192.168.5.1 ?

    >
    > Yes, they do have a route to 192.168.2.x via gateway 192.168.5.1.


    I'd still wonder about the routing tables... maybe a wrong netmask?

    You could try running wireshark on your gateway machine to see what
    packets are going where.
    --
    Joseph J. Pfeiffer, Jr., Ph.D. Phone -- (505) 646-1605
    Department of Computer Science FAX -- (505) 646-1002
    New Mexico State University http://www.cs.nmsu.edu/~pfeiffer

  8. Re: ip_forwarding / gateway

    Clifford Kite wrote:
    > Whinyan wrote:
    >> Hello,


    >> I am building a network of Linux boxes running a small self-made Linux. One
    >> of these boxes is setup as a dial-in server for the network. I have the
    >> dial-in part up and running, but have difficulties configuring the network
    >> such that I can reach the Linux boxes from out of the network.


    >> This is my setup:


    >> 192.168.2.1 <---ppp---> 192.168.2.2 <---ip_forwarding on the dial-in
    >> server---> 192.168.5.1 <--- eth ---> 192.168.5.2 <--- eth ---> 192.168.5.3
    >> etc.


    >> My dial-in server has ip address 192.168.2.2 on the ppp connection and
    >> 192.168.5.1 on the eth connection. 192.168.5.x is the Linux network.
    >> Ip_forwarding is turned on the dial-in server.


    >> Using the pc with IP address 192.168.2.1, I am able to ping the Linux
    >> dial-in server on both its IP addresses (192.168.2.2 and 192.168.5.1).
    >> However, I cannot reach the Linux boxes with IP addresses 192.168.5.2 and
    >> up. When I ping these boxes, I can see the lights of the Ethernet cards
    >> flicker, but the ping requests time out.


    >> Am I overlooking something? Any help is greatly appreciated.


    > Maybe the pppd proxyarp option?


    Duh! I belatedly realized that this option alone isn't enough, assuming
    the server LAN is 192.168.5.0/24 or similar. The dialed-in must also
    use an unassigned IP address belonging to the server LAN on it's end
    of the PPP link. If you do this, and have the right routing, then the
    dialed-in should be able to reach the LAN hosts. You also should be
    able to use 192.168.5.1 as the server's PPP IP address.

    --
    Clifford Kite

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