From mboxrd@z Thu Jan  1 00:00:00 1970
From: Martijn Lievaart <m@rtij.nl>
Subject: Re: PtP not working
Date: Sun, 21 May 2006 13:20:51 +0200
Message-ID: <44704D13.3060305@rtij.nl>
References: <200605201730.52334.antonio.dibacco@aruba.it>
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To: Antonio Di Bacco <antonio.dibacco@aruba.it>
Cc: netfilter@lists.netfilter.org

Antonio Di Bacco wrote:

>Anyone could explain this?
>
>Two linux systems connected:
>
>System A     <=========> System B
>                   eth0                    eth0
>
>Each system ha the following config:
>
># routing enabled
>net.ipv4.ip_forward=1
>
>#ethernet with no address associated and NOARP set
>eth0      Link encap:Ethernet  HWaddr 08:00:3E:26:24:65
>          UP BROADCAST RUNNING NOARP MULTICAST  MTU:1500  Metric:1
>          RX packets:1306 errors:0 dropped:0 overruns:0 frame:0
>          TX packets:1325 errors:0 dropped:0 overruns:0 carrier:0
>          collisions:0 txqueuelen:1000
>          RX bytes:732864 (715.6 KiB)  TX bytes:61643 (60.1 KiB)
>          Base address:0x3c00
>
># Routing table
>Kernel IP routing table
>Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
>10.10.10.10     *               255.255.255.255 UH    0      0        0 eth0
>
>
>I'm on System A and try to ping 10.10.10.10 but no answer. Where is the 
>problem?
>  
>

Which system has 10.10.10.10? None. So how can any system answer? Even 
if there was a 10.10.10.10, you disabled the arp mechanism, so you can 
never find out where it is. Finaly, for the return packets exactly the 
same problem occurs.

If you want to make a point to point connection over ethernet:
- Either just configure a subnet there.
- Or:
  - Assign addresses to the interfaces (can be the same address as 
another interface on the same box)
  - Create static arp addresses for the other box
  - Create routes as above for the address of the other box

I think you will still have to enable arp for this to work, in which 
case you can skip the static arp entries.

HTH,
M4