Subject: Testing my Network

From: "TJ O Connor" <[email-masked]>
Date: Mon, 24 Jul 2000 18:15:22 +0100

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Hi,
   I am after setting up my own subnet on a linux box to test my
   firewall.
   I put in a second ethernet card which installed no problem.
   When i ran a few tests on the subnet i came up against a slight
   problem.

I can ping from any computer on my subnet to the inside address of  the
firewall system and i can ping from the firewall to an internet system
(www.esat.net)
However when I try to ping the outside address of the firewall
from a computer on the subnet it lets me. I have ip_forwarding
turned off by using this command:
'echo "0" > /proc/sys/net/ipv4/ip_forward'

if anyone knows what i am talking about could they please
email me

cheers

- --                      _
T.J.O'Connor            _/ \_   2200 Cork Airport Business Park,
SysAdmin               / \_/ \  Kinsale Rd., Cork, Ireland.
Comnitel Technologies  \_/ \_/  Ph: +353 21 7305620
[email-masked]    \_/    Fax: +353 21 7305624

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From: "Y. W. Ko" <[email-masked]>
Date: Mon, 24 Jul 2000 15:59:16 -0400

I have come across this myself...

I guess that it happens when both your internal and external interface have
the same network address, in which case, the TCP/IP stack consider them to
be on the same subnet. I believe, (well, I hope anyway) that the ping that
you did from the internal network can only go as far as the external
interface, not beyond. What you might want to do is to reassign reserved
non-routable ip address such as "198.162.xxx.xxx" to your internal network.
The behaviour you described would disappear.

Hope this helps,

	Ko

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> -----Original Message-----
> From: [email-masked] [mailto:[email-masked]]On
> Behalf Of TJ O Connor
> Sent: Monday, July 24, 2000 1:15 PM
> To: Fwtk Users
> Subject: Testing my Network
>
>

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From: "Nico Baggus" <[email-masked]>
Date: Tue, 25 Jul 2000 00:53:51 +0200

----8<------
> internal network.
I do hope you mean private networks: 192.168.0.0/16 or 172.16.0.0/12 or
10.0.0.0/8
or the test network: 169.254.0.0/16

------8<-----