RE: Eth1 and eth0

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Author: Jesus E Zepeda
Date:  
To: plug-discuss
Subject: RE: Eth1 and eth0
Hi, Erik:

Yes, you are right that is a private network behind a firewall and
10.100.1.245 is the firewall's interface to the 10.100.0.0/16 network.
At this network I have Windows machines accessing the Internet. But my
computer is the only instance that has two NICs.

Craig, provided me with a pice of information that resulted an excellent
progress. I can ping on both sides of my computer and get on the
Internet now. He recommended adding at /etc/sysconfig/network these two
lines:

GATEWAYDEV=eth0
GATEWAY=10.100.1.145

Because at this moment I am not at the site where my computer is, I
setup a test environment at my office but I am lacking of a router. So,
if having 2 gateways is a nono and my computer is standing between these
two Gateway interfaces: The firewall and the internal router, I wonder
whether I will be able to access the other side of the private router as
well?

I will check on this early tomorrow, but if you guys see what my problem
is (My Computer is in between two routers and has to access both sides),
what would be the best way to attain it?

Regards,

Jesus

-----Original Message-----
From: Erik Bixby [mailto:erik.bixby@gmail.com]
Sent: Friday, April 15, 2005 14:18
To:
Subject: Re: Eth1 and eth0


In your first email you said eth0 is connected to the Internet.
However, it seems that eth0 has the IP address 10.100.1.102. Is that a
private network behind a machine doing NAT? That being the case, is its
private address 10.100.1.245? Can this machine ping that IP? Can any
machine on this private network get out? (As in, is the NAT box working
properly.)

On 4/15/05, Jesus E Zepeda <> wrote:
> Hi, Craig:
>
> I tried setting the Gateway to eth0 with no positive result.
> Eventhough both are on the same machine the subnet is different.
>
> As far as acting as a router, the /proc/sys/net/ipv4/ip_forward is
> equal 1
>
> These are the outputs you instructed:
>
> Thanks. Jesus...
> -----
> route -n
> 
> [root@custom1 root]# route -n
> Kernel IP routing table
> Destination     Gateway         Genmask         Flags Metric Ref
Use
> Iface
> 192.168.1.0     0.0.0.0         255.255.255.0   U     0      0
0
> eth1
> 10.100.0.0      0.0.0.0         255.255.0.0     U     0      0
0
> eth0
> 169.254.0.0     0.0.0.0         255.255.0.0     U     0      0
0
> eth0
> 127.0.0.0       0.0.0.0         255.0.0.0       U     0      0
0
> lo
> 0.0.0.0         10.100.1.245    0.0.0.0         UG    0      0
0
> eth0
> [root@custom1 root]#
> 
> -----
> [root@custom1 root]# ifconfig -a
> eth0      Link encap:Ethernet  HWaddr 00:A0:CC:D9:7D:E0
>           inet addr:10.100.1.102  Bcast:10.100.255.255
Mask:255.255.0.0
>           inet6 addr: fe80::2a0:ccff:fed9:7de0/64 Scope:Link
>           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
>           RX packets:234 errors:1 dropped:0 overruns:0 frame:0
>           TX packets:321 errors:523 dropped:0 overruns:0 carrier:1042
>           collisions:0 txqueuelen:1000
>           RX bytes:23727 (23.1 Kb)  TX bytes:36623 (35.7 Kb)
>           Interrupt:9 Base address:0x1400

> 
> eth1      Link encap:Ethernet  HWaddr 00:50:04:D8:79:A3
>           inet addr:192.168.1.204  Bcast:192.168.1.255 
> Mask:255.255.255.0
>           inet6 addr: fe80::250:4ff:fed8:79a3/64 Scope:Link
>           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
>           RX packets:4712 errors:0 dropped:0 overruns:1 frame:0
>           TX packets:3718 errors:0 dropped:0 overruns:0 carrier:0
>           collisions:0 txqueuelen:1000
>           RX bytes:648107 (632.9 Kb)  TX bytes:739930 (722.5 Kb)
>           Interrupt:11 Base address:0x1800

> 
> 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:5402 errors:0 dropped:0 overruns:0 frame:0
>           TX packets:5402 errors:0 dropped:0 overruns:0 carrier:0
>           collisions:0 txqueuelen:0
>           RX bytes:2746643 (2.6 Mb)  TX bytes:2746643 (2.6 Mb)

> 
> sit0      Link encap:IPv6-in-IPv4
>           NOARP  MTU:1480  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:0
>           RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b)

>
> ------
> cat /etc/sysconfig/network-scripts/ifcfg-eth0
>
> [# Please read /usr/share/doc/initscripts-*/sysconfig.txt
> # for the documentation of these parameters.
> IPV6INIT=no
> ONBOOT=yes
> USERCTL=no
> PEERDNS=yes
> GATEWAY=10.100.1.245
> TYPE=Ethernet
> DEVICE=eth0
> HWADDR=00:a0:cc:d9:7d:e0
> BOOTPROTO=none
> NETMASK=255.255.0.0
> IPADDR=10.100.1.102
>
> ----------
> cat /etc/sysconfig/network-scripts/ifcfg-eth1
>
> # Please read /usr/share/doc/initscripts-*/sysconfig.txt
> # for the documentation of these parameters.
> IPV6INIT=no
> ONBOOT=yes
> USERCTL=no
> PEERDNS=yes
> GATEWAY=10.100.1.102
> TYPE=Ethernet
> DEVICE=eth1
> HWADDR=00:50:04:d8:79:a3
> BOOTPROTO=none
> NETMASK=255.255.255.0
> IPADDR=192.168.1.204
>
> -----
> cat /etc/sysconfig/network
>
> NETWORKING=yes
> HOSTNAME=custom1
>
> -----Original Message-----
> From: Craig White [mailto:craigwhite@azapple.com]
> Sent: Friday, April 15, 2005 10:55
> To:
> Subject: Re: Eth1 and eth0
>
> On Fri, 2005-04-15 at 10:34 -0700, Jesus E Zepeda wrote:
> > Hello, list:
> >
> > I am using Fedora Core 2 in my computer, which is setup with two
> > NICs:
>
> > Eth1 NIC is connected to the LAN; and eth0 connected to the
> > Internet. Also, eth1 NIC has as a gateway an interface of a router.
> >
> > Both eth0 and eth1 are active. I can ping from one another interface

> > and to any host on either side. The problem I have is that I cannot
> > reach the other side of the router.
> >
> > What can I do to be able to have my computer talk to both sides and
> > across the router, when I know that the router will reply on the
> > other
>
> > side if I have eth0 (Internet) removed?
> ----
> seems to me that the gateway device should be eth0.
>
> it would be easier if you gave us the output of...
>
> route -n
>
> ifconfig -a
>
> cat /etc/sysconfig/network-scripts/ifcfg-eth0
>
> cat /etc/sysconfig/network-scripts/ifcfg-eth1
>
> cat /etc/sysconfig/network
>
> also, to act as a router, your probably need to do some things like...

> echo "1" > /proc/sys/net/ipv4/ip_forward
>
> suggest that you look at...
> http://www.ecst.csuchico.edu/~dranch/LINUX/ipmasq/c-html/stronger-
> firewall-examples.html#RC.FIREWALL-2.4.X-STRONGER
>
> Craig
>
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