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Re: Routing table drops packets via ppp0

Greg Folkert wrote:
On Tue, 2003-10-21 at 03:39, Mark Devin wrote:

I am having some trouble getting routing to work properly on a box with three network connections. One, eth0, is connected to a router and is the default gateway. Another, ppp0 (eth1 - ADSL) is connected to a private network on the address range. The third is a standard LAN (eth2) on

From the debian box, I can ping other machines connected via the ADSL modem via ppp0. I can also ping machines on the internet via eth0 from this box. In addition, any machine on the Office LAN can connect to machines on the internet.

However, if a machine on the office LAN tries to connect to a machine on the network, the packets disappear somewhere in the debian box. I can see the packets coming in with tcpdump but then they disappear. The debian box does not try to route them at all.

Note that I have switched off all firewalling and switched ip_forwarding on in the kernel.

The problem is related to the ADSL - ppp0 interface. The routing rules look OK. I can ping from the debian box via ppp0 to hosts on the connected network. However, if I ping from the office LAN, the packets do get to the debian box OK, but it doesn't route them out ppp0. It just seems to drop them. There is nothing in the logs to indicate any errors. The packets just disappear.

The setup looks like this:

    x.x.47.224/27 Router x.x.47.225
  eth0| x.x.47.226
#------------#  (eth1 -ppp0 ADSL)
# Debian Box #-->x.x.16.78-->
   Office LAN (

The routing table looks like:
# route -n
Destination     Gateway         Genmask        Flag Met Ref Use Iface
x.x.16.78 UH   0  0  0   ppp0
x.x.243.224 U    0  0  0   eth0   U    0  0  0   eth2    x.x.16.78   UG   0  0  0   ppp0         x.x.243.225         UG   0  0  0   eth0

Silly question:

Are you running a routing daemon?

No.  Are you talking about the ARP daemon support in the kernel?

I have compiled my own kernel for this box and it doesn't have the ARP daemon support.

What I can't understand is that the box will route packets correctly when they are generated on the box itself. I have ip_forwarding switched on and yet it seems to drop packets somewhere when it should be routing them. I can see packets coming in but they don't go out.

Is there anyway that I can log what is happening in the routing process?


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