[SOLVED] One-way pings in the home LAN

phoederr · 2009-01-11 17:36:47

I'm trying to set up a home LAN of two computers -- one of my own with Arch installed (#1) and my wife's one with WindowsXP on it (#2). #1 is connected to internet via pppoe on eth0 and to #2 on eth1; #2 connected only to #1 with an only network card.
I encountered a strange problem: while i can ping #2 from #1 with ping -I eth1 192.168.0.3, pinging from #2 back to #1 is impossible.

#1 has the followin configuration:

bash-3.2# ifconfig
eth0 Link encap:Ethernet HWaddr 00:08:A1:90:E5:29
inet addr:192.168.0.1 Bcast:192.168.0.255 Mask:255.255.255.0
inet6 addr: fe80::208:a1ff:fe90:e529/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:15452 errors:0 dropped:0 overruns:0 frame:0
TX packets:17188 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:10622616 (10.1 Mb) TX bytes:2581935 (2.4 Mb)
Interrupt:18 Base address:0xd000
eth1 Link encap:Ethernet HWaddr 00:1B:11:B7:F2:2A
inet addr:192.168.0.2 Bcast:192.168.0.255 Mask:255.255.255.0
inet6 addr: fe80::21b:11ff:feb7:f22a/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:6 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:0 (0.0 b) TX bytes:468 (468.0 b)
Interrupt:17 Base address:0xd400
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:0 (0.0 b) TX bytes:0 (0.0 b)
ppp0 Link encap:Point-to-Point Protocol
inet addr:94.181.94.19 P-t-P:91.144.140.70 Mask:255.255.255.255
UP POINTOPOINT RUNNING NOARP MULTICAST MTU:1492 Metric:1
RX packets:15192 errors:0 dropped:0 overruns:0 frame:0
TX packets:16992 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:3
RX bytes:10255155 (9.7 Mb) TX bytes:2202091 (2.1 Mb)

#2 is configured like that:

IP: 192.168.0.3
netmask: 255.255.255.0
gateway: 192.168.0.2

What could be the reason?

Last edited by phoederr (2009-01-12 16:26:15)

Xyne · 2009-01-11 19:39:48

The first thing I would check is if you have an improperly configured firewall.

Dieter@be · 2009-01-11 21:18:13

which iface is listed next to the default route for the 192.168.0.* or 192.168.* network? (check with `route`). It could be that it's eth0 and Linux will perform internal routing. to solve that you can setup source routing, change your default route (but then you can't ping from your router) or take another range for the local network.

Why have you such a weird setup anyway? physical constraints?

Xyne · 2009-01-11 22:01:34

Dieter@be wrote:

Why have you such a weird setup anyway? physical constraints?

Maybe he just wants to control his wife's internet access.

fukawi2 · 2009-01-11 22:17:55

phoederr wrote:

bash-3.2# ifconfig
eth0 Link encap:Ethernet HWaddr 00:08:A1:90:E5:29
inet addr:192.168.0.1 Bcast:192.168.0.255 Mask:255.255.255.0
eth1 Link encap:Ethernet HWaddr 00:1B:11:B7:F2:2A
inet addr:192.168.0.2 Bcast:192.168.0.255 Mask:255.255.255.0

You shouldn't have both network interfaces with the same IP range. What is happening is:
1. #2 sends echo request packet to #1
2. #1 recieves and examines the packet, and see's that it's from 192.168.0.3
3. #1 examines the route table, and the first and most specific route that 192.168.0.3 matches will be eth0, so it sends the echo reply via eth0 -- naturally this will never get back to #2.

This is also the reason you have to specifically tell ping to use eth1 when #1 pings #2.

Change the IP range on eth2 to 192.168.1.x instead of 192.168.0.x and you'll be on the right track

phoederr · 2009-01-12 16:35:43

Thanks for your help!
It helped when I've changed eth1 IP to 192.168.1.1 (And #2 respectively to 192.168.1.2).

Dieter@be wrote:

Why have you such a weird setup anyway? physical constraints?

More of a mental disorder rather than a physical constraint -- I'd just got no previous experience with networking, so I simply followed http://wiki.archlinux.org/index.php/Internet_Share and carefully copied everything up to the IP.

Arch Linux

#1 2009-01-11 17:36:47

[SOLVED] One-way pings in the home LAN

#2 2009-01-11 19:39:48

Re: [SOLVED] One-way pings in the home LAN

#3 2009-01-11 21:18:13

Re: [SOLVED] One-way pings in the home LAN

#4 2009-01-11 22:01:34

Re: [SOLVED] One-way pings in the home LAN

#5 2009-01-11 22:17:55

Re: [SOLVED] One-way pings in the home LAN

#6 2009-01-12 16:35:43

Re: [SOLVED] One-way pings in the home LAN

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