[LARTC] possible packet forwarding or routing problem

[LARTC] possible packet forwarding or routing problem

[John covici]

Hi.  I have a system with two network cards -- eth0 is a public ip
address and eth1 is on an internal network.  Now I have all the packet
forwards enabled, and there is a route from eth1 to the internal
network, but if a computer on the internal network sets his gateway to
the box, he can't traceroute  past the box to the internet.   There
are no iptable rules yet.

Here is the routing table as produced by route.
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
64.183.125.208  *               255.255.255.248 U     0      0        0 eth0
192.168.1.0     *               255.255.255.0   U     0      0        0 eth1
169.254.0.0     *               255.255.0.0     U     0      0        0 eth0
default         rrcs-64-183-125 0.0.0.0         UG    0      0        0 eth0


What am I doing wrong here?

Any assistance would be appreciated.

-- 
Your life is like a penny.  You're going to lose it.  The question is:
How do
you spend it?

         John Covici
         covici@ccs.covici.com
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Re: [LARTC] possible packet forwarding or routing problem

[David Hough]

John covici wrote:
> Hi.  I have a system with two network cards -- eth0 is a public ip
> address and eth1 is on an internal network.  Now I have all the packet
> forwards enabled, and there is a route from eth1 to the internal
> network, but if a computer on the internal network sets his gateway to
> the box, he can't traceroute  past the box to the internet.   There
> are no iptable rules yet.
> 
> Here is the routing table as produced by route.
> Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
> 64.183.125.208  *               255.255.255.248 U     0      0        0 eth0
> 192.168.1.0     *               255.255.255.0   U     0      0        0 eth1
> 169.254.0.0     *               255.255.0.0     U     0      0        0 eth0
> default         rrcs-64-183-125 0.0.0.0         UG    0      0        0 eth0
> 
> 
> What am I doing wrong here?
> 
> Any assistance would be appreciated.
> 
Two things spring to mind.

1. What result do you get from "cat /proc/sys/net/ipv4/ip_forward"? If
it's zero then you haven't got forwarding enabled.

2. Even if it is enabled, stuff on the LAN will head out to the big wide
world with a 192.168.1.x address on it and get eaten by any
properly-configured router outside.

To fix the first one, just "echo 1 > /proc/sys/net/ipv4/ip_forward" to
enable forwarding.

To fix the second one, you'll need a bunch of iptables rules to set up
NAT so all outbound traffic goes out using your public IP.
-- 
Dave
http://www.llondel.org
So many gadgets, so little time
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Re: [LARTC] possible packet forwarding or routing problem

[John covici]

on Sunday 01/28/2007 David Hough(lists@llondel.org) wrote
 > John covici wrote:
 > > Hi.  I have a system with two network cards -- eth0 is a public ip
 > > address and eth1 is on an internal network.  Now I have all the packet
 > > forwards enabled, and there is a route from eth1 to the internal
 > > network, but if a computer on the internal network sets his gateway to
 > > the box, he can't traceroute  past the box to the internet.   There
 > > are no iptable rules yet.
 > > 
 > > Here is the routing table as produced by route.
 > > Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
 > > 64.183.125.208  *               255.255.255.248 U     0      0        0 eth0
 > > 192.168.1.0     *               255.255.255.0   U     0      0        0 eth1
 > > 169.254.0.0     *               255.255.0.0     U     0      0        0 eth0
 > > default         rrcs-64-183-125 0.0.0.0         UG    0      0        0 eth0
 > > 
 > > 
 > > What am I doing wrong here?
 > > 
 > > Any assistance would be appreciated.
 > > 
 > Two things spring to mind.
 > 
 > 1. What result do you get from "cat /proc/sys/net/ipv4/ip_forward"? If
 > it's zero then you haven't got forwarding enabled.
 > 
 > 2. Even if it is enabled, stuff on the LAN will head out to the big wide
 > world with a 192.168.1.x address on it and get eaten by any
 > properly-configured router outside.
 > 
 > To fix the first one, just "echo 1 > /proc/sys/net/ipv4/ip_forward" to
 > enable forwarding.
 > 
 > To fix the second one, you'll need a bunch of iptables rules to set up
 > NAT so all outbound traffic goes out using your public IP.
 > -- 
 > Dave
 > http://www.llondel.org
 > So many gadgets, so little time
 > _______________________________________________
 > LARTC mailing list
 > LARTC@mailman.ds9a.nl
 > http://mailman.ds9a.nl/cgi-bin/mailman/listinfo/lartc

-- 
Your life is like a penny.  You're going to lose it.  The question is:
How do
you spend it?

         John Covici
         covici@ccs.covici.com
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