Can't trace a host even when it is in ARP table

Asked by Oscar Ramos on 2013-02-02

I have an ubuntu machine with 3 eth interfaces and 1 wlan, I have create next routes:

eth1
    post-up /sbin/route add -host 10.80.203.166 dev eth1
    pre-down /sbin/route del -host 10.80.203.166 dev eth1
eth2
    post-up /sbin/route add -host 192.168.200.8 dev eth2
    pre-down /sbin/route del -host 192.168.200.8 dev eth2

my route table is:

Destination Gateway Genmask Flags Metric Ref Use Iface
192.168.200.8 0.0.0.0 255.255.255.255 UH 0 0 0 eth2
10.80.203.92 0.0.0.0 255.255.255.255 UH 0 0 0 eth1
192.168.77.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0
10.80.203.0 0.0.0.0 255.255.255.0 U 0 0 0 wlan0
0.0.0.0 10.80.203.254 0.0.0.0 UG 0 0 0 wlan0

my arp table is

? (10.80.203.254) at 00:00:0c:07:ac:cb [ether] on wlan0
? (10.80.203.92) at 00:d0:dc:07:3e:4d [ether] on eth1
? (192.168.200.8) at 00:20:98:01:d7:63 [ether] on eth2
? (10.80.203.2) at 00:0c:29:04:88:49 [ether] on wlan0
? (10.80.203.3) at 00:0c:29:a0:71:1c [ether] on wlan0
? (10.80.203.99) at dc:9f:db:22:92:e2 [ether] on wlan0

When I do a tcpdump -i eth2 I can see traffic from 10.80.203.92 going to 192.168.200.8, but I can't see any traffic from 192.168.200.8 to 10.80.203.92 and also I can't ping the 192.80.203.92. I have also noticed when eth1 is not connected I can see traffic from 192.168.200.8 but as soon as I coonect eth1 I just can see the traffic from eth1 to eth2 on eth2 port

Any help will be appreciated

Oscar

Question information

Language:
English Edit question
Status:
Answered
For:
Ubuntu network-manager-applet Edit question
Assignee:
No assignee Edit question
Last query:
2013-02-03
Last reply:
2013-02-03
Oscar Ramos (ramses-vii) said : #1

one correction, the route I created on eth1 was 10.80.203.92 not 166

Oscar Ramos (ramses-vii) said : #2

one more correction: I can't ping 192.168.200.8, but I can ping 10.80.203.92

Thomas Krüger (thkrueger) said : #3

Your network setup is kinda ubnusual. What are you actually trying to do and how does your physical network topology look like?

Oscar Ramos (ramses-vii) said : #4

well on the Eth2 I have a device that send out information over Ethernet (IP:192.168.200.8), there is no way to change the IP; on the Eth1 there is a windows device with a software on it that collect and process all the info from the device but it only has 1 Ethernet port and it is necessary to send all the info through the network, that is why I am using the Linux - Ubuntu Machine and trying to route all the traffic between both devices and sent it over ethernet

Thomas Krüger (thkrueger) said : #5

So, it looks like this?

------- ----------------- -------
| D1 | --- (2)| Ubuntu PC |(1) --- | D2 |
------- ----------------- -------

And you want D1 to communicate with D2?
I that case you have to setup two different subnets (and not only hosts routes) on both eth1 and eth2 and set the default route (or a specific route to the other network) on both devices (D1, D2) to the IP of the router in the subnet they are connected to.

Example
D1: 10.0.0.1/24 default gw 10.0.0.254
D2: 192.168.200.8 default gw 192.168.200.254
Ubuntu
  eth1: 10.0.0.254/24 default gw (your router)
  eth2: 192.168.200.254/24

Or you have to bridge the adapter. https://help.ubuntu.com/community/NetworkConnectionBridge

But frankly it would be far more easy to use one network with a switch and assign a secondary IP to the devices that need to communicate with device that has a fixed IP.

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