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Old 06-27-2005, 02:11 AM   #1
Z8002
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Why can I not ping two networks?


I can see that my last question was too vague, sorry.

If I have two etherenet cards; eth0 connects to a machine 192.168.0.2 and eth1 to 192.168.0.99, then why does the following happen?

ping 192.168.0.99 .............. reply

ping 192.168.0.2 .............. unreachable

ping -I eth0 192.168.0.2 ....... reply


How do I configure my network so that ping will try both by default, without my having to specify the interface to be pinged?


If anyone can help, I'll be grateful.
 
Old 06-27-2005, 02:41 AM   #2
mmmm
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Type : `netstat -r`
It lists route tables from kernel.
It sth like :
Destination Gateway Genmask Flags MSS Window irtt Iface
10.1.2.0 * 255.255.255.0 U 0 0 0 eth0
default ´my gateway´ 0.0.0.0 UG 0 0 0 eth0
What does it mean ? It says kernel :
1. If packet is to 10.1.2.* send it throw eth0
2. Else - send throw eth0
On you comp it should be :
192.168.0.99 * 255.255.255.0 U 0 0 0 eth1
192.168.0.2 * 255.255.255.0 U 0 0 0 eth0
It will say kernel the same, that you say by ´-l eth0´
If you cant configure it, I can help you, but you must post output of ´netstat -r´
 
Old 06-27-2005, 07:24 AM   #3
stefan_nicolau
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You have probably configured two overlaping networks, something like:
192.168.0.99/24 eth1
192.168.0.2/24 eth0

This means that anything in the 192.168.0.1-192.168.0.255 range is sent through eth1

post the output of 'ifconfig -a' and 'route' (route is the same as netstat -r)

Please use different logical networks for different physical networks:
192.168.0.0/24 eth0
192.168.1.0/24 eth1
 
Old 06-27-2005, 09:40 AM   #4
baldy3105
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This is normal behaviour. You have just confused the poor machine. When you configure an address of 192.168.0.1 255.255.255.0 on an interface the OS will create a route 192.168.0.0 that points to the interface as a directly connected network. You now stick 192.168.0.99 255.255.255.0 on another interface, the OS will create another 192.168.0.0 route pointing out of that. When you attempt to send packets to 192.168.0.0 they match the first entry in the table and will never get as far as the second unless the first goes down.
 
Old 06-27-2005, 02:48 PM   #5
Z8002
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Thank you all for your help.

After reading your replies, I dug out a textbook and read up on ip addresses and sub networks.

I settled for a netmask of 255.255.255.224, to give me six networks from 192.168.0.x


I used addresses from the 192.168.0.32 network for eth0 and all the devices on my LAN,

I used addresses from the 192.168.0.160 network for eth1 and all the kit connecting to the ADSL modem.

Four spare networks left for future expansion..


Suddenly, everything started working. Most excellent.


I'm sure this seems pretty basic to you chaps, but no-one had ever told me what was required before and you've made me a very happy man.
 
Old 07-05-2005, 10:49 AM   #6
baldy3105
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Glad to be of assistance :-)
 
  


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