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pppd works but I have a routing problem

mag062397 asked
Last Modified: 2010-04-20
I'm using ppp to connect my laptop computer to my network at work which is connect to the internet.

I can connect the two together using ppp/chat however I can't see beyond the network computer.  I can't even see other computers on the network (using ping), let along the internet.

I'm using the defaultroute option on my laptop and I'm using the proxyarp option on the network PC.  If I ping another computer on the network from my laptop, the packets are being transmitted from the laptop and they are be received by the network computer; however the network computer is not retransmitting them out its eth0 port.

I determined this by monitoring the /proc/net/dev file on each computer.

I'm using Redhat 5.1

What am I missing?
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I suppose you have installed Linux on your network computer. Did you compile your kernel with IP-masquerading?


Yes I have linux (Redhat 5.1) installed on both computers.

No, I don't think IP-masquerading is compilied in. Is there an easy why to find out.

Is it really needed?  I can get my laptop to talk correctly to another linux box that I have here.  However, the person that configured that box no longer works here.  And it is a really old version of linux (kernel 1.2.8).  

I assume you can ping other machines in your network and on the Internet from your network PC.  What happens when you try to ping the laptop from the network PC?
1. Is your network connected to the internet through a proxy server or through a direct connection/router?
2. Is your linux box connected to your network using a network card (you talk about eth0)?

If answer to 1 and 2 is yes, why you are using pppd/chat? You need only to configure your net card to have an IP compatible with your network and to use the same gateway to the internet (proxy server or router). Also, you do not need IP masquerade (I assume you want your linux box as a client; IP masquerade is for using the linux box as a router).
Ops, I misunderstood your question first time, forget the comment above.

If you are dialing from your laptop to a network PC, both running Linux, the solution for your problem depends on the IP your laptop is receiving from the network PC (and this depends on the IP your network PC has in the net card).

If the network PC is directly connected to the internet (or the net card IP is a public one) this box should be configured with IP forward. If this net PC is connected by a proxy or similar (and the net card IP is a private one), then this PC should be configured with IP masquerade.

In any case, look in the man pages for "ipfwadm" cause you will need this.

RH5.1 includes IP masquerading support in the kernel by default.
Can you ping the laptop while logged into the "network computer"?

The problem is either that
  1) The N.C. does not have IP forwarding turned on
     solution: set FORWARD_IPV4=yes in /etc/sysconfig/netwwork
     then restart networking with
      /etc/rc.d/init.d/network restart
   2) IP forwarding is on, but the machines on the far side of
      the N.C. think that to send packets to your laptop's
      IP address, they have to send them somewhere other than
      to the N.C.  
        solution: either update the routing tables on those hosts,
        or set up IP Masquerading on the N.C.,
        or select an IP address for the laptop which is compatible with the routing assumptions made by all the other machines.

IP Masquerading is explained in one of the HOWTOs.


Thanks to all.  The following fixed it for me.

 1) The N.C. does not have IP forwarding turned on
            solution: set FORWARD_IPV4=yes in /etc/sysconfig/netwwork
            then restart networking with
             /etc/rc.d/init.d/network restart

To answer some of the questions above.  Yes I connect to the internet with a dedicated line (router and T1).  And no I wasn't able to ping the laptop from another computer on the network.

BUT I CAN NOW.  YEAH!!!   :)

Thanks again.  I guess JYoungman should submit a "Proposed Answer" so that I can accept it.
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