RE: 2 NIC cards not talking

Ray Olszewski
2004-01-21T17:08:24Z

At 10:23 AM 1/21/2004 -0500, Chadha, Devesh wrote:
>Juan,
>
>Eth0 has the external assigned IP by my ISP. Eth1 has a 192.168.x.x ip
>address. Eth1 acts as the DHCP server for my LAN. My LAN is working fine. I
>can connect machines to the LAN and even connect one machine to another.
>
>But I cannot get eth1 to talk to eth0. I cannot connect the LAN to the
>internet nor connect to any internal machine from outside!!
>
>Do I need to bridge the 2 NICs ???

This description is better than your first try, but it still leaves out way
too much information. Terms like "connect" and "talk to" are, in this
context, too vague, and interfaces don't "talk to" each other by any
reasonable definition of "talk to". Moreover, some of what you say here
appears inconsistent with the first report (or perhaps you changed your
setup between them). So please go step by step and give us the required
details.

1. What is the physical setup here? In this second message, you talk about
connecting "the LAN to the internet", but the first message said bith NICs
were "on the same subnet". Is this 2-NIC Linux host intended to act as a
router or not (I'm guessing yes)? If yes, does it need to NAT or not (I'm
guessing it does)?

2. What are the actual IP addresses involved, and what does the routing
table on the Linux host look like? (IP addresses are not secrets, after
all.) Show us the output of

ifconfig -a [the complete entries for eth0 and eth1]
netstat -nr

3. Assuming the Linux host is supposed to be acting as a router, do you
have it configured to do so? First, is ip_forwarding turned on (that is,
does "more /proc/sys/net/ipv4/ip_forward" return a "1")? Second, assuming I
read this correctly that the LAN uses private IP addresses
(192.168.c.d/16-24) and the ISP side a public address you have not
identified, you you have iptables set up to NAT the LAN?

4. What actual tests are you making, and what are their actual results?
Hosts don't "talk to" each other. They "ping", and "telnet", and "ssh", and
a bunch of other things ... we need to know what fails (and how -- ping,
for example, fails in at least 4 distinct ways) to be able to diagnnose a
problem beyond offering wild guesses (as I have above).

5. Can the Linux router itself ping, or make other connections, to Internet
hosts? That is, does eth0 work at all, as configured? Be specifc in your
response about what tests you emplyed to answer this.

6. If you do post again, please include the basics of your setup: What
Linux distro and version, what kernel ("uname -a"), what NICs, and the
specifics I asked for above. Note the number of times I had to "guess" or
"assume" something, and it will tell you how much important detail you've
left out.

If I'm ***guessing*** correctly about your setup, you need to be NAT'ing a
private-address LAN. If so, you will, with a bit of work, be able to set it
up so that the LAN hosts can initiate connections to Internet hosts
(assuming your ISP is not doing something unusual with your service). But
setting things up to that Internet hosts can initiate connections to LAN
hosts will be more involved, and more limited, since they all share a
single public (routable) IP address ... you'll need to use port forwarding
(DNAT, in iptables terms) and make only one host available per service.

Finally, and just as a matter of form, I must object to you (or anyone)
posting messages to this list with the assertion that they are
"confidential" and that "any review, dissemination, distribution or
copying of this message is strictly prohibited". I understand that the
attachment of this baloney is outside your personal control ... but it is
baloney nonetheless, and you and your employer need to understand that it
is made meaningless by the act of you sending the message to a mailing list.

>-----Original Message-----
>From: Juan Facundo Suárez [mailto:facundo.suarez@ensi.com.ar]
>Sent: Wednesday, January 21, 2004 10:13 AM
>To: linux-newbie list
>Subject: Re: 2 NIC cards not talking
>
>
>Sorry, i don't understand at all. You say that you have two cards, in the
>same machine, are them in the same subnet ? why don't you put one, wich
>connects to "outside" in one, and the other in another subnet?. I have
>working a firewall/router with iptables, and the card is connected to de
>adsl-modem has 192.168.1.10, and the card to brins internet to the lan has
>192.168.0.1.
>
> If you cannot ping from a machine in one subnet, to another in other
>subnet, maybe you need to load the kernel-module wich does that job.
>
>--
>Facundo Suárez
>Neuquén - Argentina
>FDSoft
>mail y jabber: faco@fdsoft.com.ar
>facundo.suarez@ensi.com.ar
>
>----- Original Message -----
>From: "Chadha, Devesh" <devesh.chadha@lehman.com>
>To: <linux-newbie@vger.kernel.org>
>Sent: Wednesday, January 21, 2004 11:25 AM
>Subject: 2 NIC cards not talking
>
>
>| Hi,
>|
>| I have a linux box with 2 NIC cards, both are properly configured.
>| Both
>are
>| on the same subnet, but still don't ping to one another!!
>|
>| I need to setup the box as the firewall/router that has eth0 set as
>external
>| and eth1 as internal serving as DHCP server to other computers on the
>| network. Both have static IPs assigned to them.

[boilerplate baloney deleted]