How can I ping through different interfaces (subnets) without using a router device?

Question

I have a big problem around this issue.

I want to be able to ping and access TFTP through my WIFI interface (wlan0) through my wired interface (eth0)

pc1_eth->LTdhcps2_eth0->LTdhcps2_wlan0->pc2_wlan

and the reverse

pc2_wlan->LTdhcps2_wlan0->LTdhcps2_eth0->pc1_eth

At first I thought that it would be simple because I assumed that I only need to set the gateway of my eth0 with my wlan0's IP.

I was wrong, I was unable to accomplish that.

Let the pain begins..

1) I think the configuration from pc1 and pc2 doesnt metter because it only involves the LTdhcps2 interfaces, am I right ?

Server LTdhcps2

Eth0

cat /etc/network/interfaces
# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).

# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
#allow-hotplug eth0
#iface eth0 inet dhcp

auto eth0
iface eth0 inet static
    address 192.168.2.10
    netmask 255.255.255.0

WLAN0

is DHCP configured by network-manager (I couldn't figured out how can I configure it using wpa_supplicant)

After starting the services

service network-manager start
service networking start

this the result

[root@LTdhcps2:~]# ifconfig 
eth0      Link encap:Ethernet  HWaddr 00:1e:c9:24:c9:d1  
          inet addr:192.168.2.10  Bcast:192.168.2.255  Mask:255.255.255.0
          UP BROADCAST MULTICAST  MTU:1500  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:1000 
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)
          Interrupt:44 Base address:0xc000 

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:20 errors:0 dropped:0 overruns:0 frame:0
          TX packets:20 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:1348 (1.3 KiB)  TX bytes:1348 (1.3 KiB)

wlan0     Link encap:Ethernet  HWaddr 00:24:2b:c7:74:7e  
          inet addr:10.0.2.218  Bcast:10.0.3.255  Mask:255.255.252.0
          inet6 addr: fe80::224:2bff:fec7:747e/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:24154 errors:0 dropped:0 overruns:0 frame:37468
          TX packets:677 errors:8 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:1670308 (1.5 MiB)  TX bytes:140171 (136.8 KiB)
          Interrupt:19

[root@LTdhcps2:~]# route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
0.0.0.0         10.0.1.2        0.0.0.0         UG    0      0        0 wlan0
10.0.0.0        0.0.0.0         255.255.252.0   U     0      0        0 wlan0
192.168.2.0     0.0.0.0         255.255.255.0   U     0      0        0 eth0


[root@LTdhcps2:~]# netstat -rn
Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
0.0.0.0         10.0.1.2        0.0.0.0         UG        0 0          0 wlan0
10.0.0.0        0.0.0.0         255.255.252.0   U         0 0          0 wlan0
192.168.2.0     0.0.0.0         255.255.255.0   U         0 0          0 eth0

what I've tried to do.

[root@LTdhcps2:~]# route add -net 10.0.0.0 gw 10.0.2.218 dev eth0
SIOCADDRT: Invalid argument
[root@LTdhcps2:~]#

Strange error that means nothing =| I googled and find this post: http://www.adminsehow.com/2011/09/gateway-on-a-different-subnet-on-linux/

it says that you have to add a host with the desired gateway IP because the gateway is in a different subnet.

[root@LTdhcps2:~]# route add -host 10.0.2.218/32 dev eth0
[root@LTdhcps2:~]# route add default gw 10.0.2.218

(if I put the dev eth0 at the end of the second command) it gives the SIOCADDRT: No such process error.

as result:

[root@LTdhcps2:~]# route
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
default         10.0.2.218      0.0.0.0         UG    0      0        0 wlan0
default         10.0.1.2        0.0.0.0         UG    0      0        0 wlan0
10.0.0.0        *               255.255.252.0   U     0      0        0 wlan0
10.0.2.218      *               255.255.255.255 UH    0      0        0 eth0
192.168.2.0     *               255.255.255.0   U     0      0        0 eth0

[root@LTdhcps2:~]# netstat -rn
Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
0.0.0.0         10.0.2.218      0.0.0.0         UG        0 0          0 wlan0
0.0.0.0         10.0.1.2        0.0.0.0         UG        0 0          0 wlan0
10.0.0.0        0.0.0.0         255.255.252.0   U         0 0          0 wlan0
192.168.2.0     0.0.0.0         255.255.255.0   U         0 0          0 eth0

But I was unable to ping/traceroute wlan0 using the eth0 interface or its gateway (10.0.1.2)

[root@LTdhcps2:~]# ping -I eth0 10.0.2.218
PING 10.0.2.218 (10.0.2.218) from 192.168.2.10 eth0: 56(84) bytes of data.
From 192.168.2.10 icmp_seq=1 Destination Host Unreachable
From 192.168.2.10 icmp_seq=2 Destination Host Unreachable

[root@LTdhcps2:~]# ping -I eth0 10.0.1.2
PING 10.0.1.2 (10.0.1.2) from 192.168.2.10 eth0: 56(84) bytes of data.
From 192.168.2.10 icmp_seq=1 Destination Host Unreachable
From 192.168.2.10 icmp_seq=2 Destination Host Unreachable

[root@LTdhcps2:~]# traceroute -i  eth0 10.0.2.218
traceroute to 10.0.2.218 (10.0.2.218), 30 hops max, 60 byte packets
 1  * * *
 2  * * *
 3  * * *
 4  * * *

Sorry for the long post and bad English. I'm facing this problem the holy week =|

`I want to be able to ping and access TFTP through my WIFI interface (wlan0) through my wired interface` - Cannot parse, does not compute. Please restate. — Zoredache, Jul 05 '13 at 21:52
Its a long history. But for solve my problem I need route my wired connection through my wifi connection using my linux server as a router. eg. PC1 need to ping another PC that is connected by wireless in the server. Its not that hard to explain, what I need is the route between the two interfaces. Maybe because my English level I couldn't do it properly. — MaikoID, Jul 08 '13 at 03:08

score 1 · Accepted Answer · answered Jul 08 '13 at 20:09

1

I solved the question.

ping -I interface or traceroute -i interface

They aren't the way to check if its working, you don't need to specif the interface because if you do the kernel doesn't use the route table (I guess).

answered Jul 08 '13 at 20:09

MaikoID

151
1
7

For what it's.worth, MacOS `ping` has a `-b` option which allows you to select an interface. The man page says this is an Apple addition, so I guess it's not supported on other BSD-based systems. – tripleee Apr 28 '20 at 15:23

How can I ping through different interfaces (subnets) without using a router device?

1 Answers1