Is:
a) your addressing and routing set up correctly and/or
b) your masquerading or NAT rules set up correctly?
-d
Meir wrote:
> Hi,
>
> Sorry to bother you with this, but I try linux-net and get no
> answer (for now).
>
> I have a curious problem.
>
> My box (linux) is trying to send mail to a target.
> Between my box and the target there is a linux box 2.2.12
> with 4 NICs but (for now) _without_ any filtering rules
> at all (all default to ACCEPT).
>
> Only 2 NICs are up: eth0 to external net and eth1 to internal net.
>
> The problem is that when I tcpdump the 2 NICs from this middle-box,
> I can see a SYN getting out from eth1 and then passed to eth0
> (ip forwarding is enabled), and then I receive a SYN/ACK from the
> target box via eth0, but this SYN/ACK _never_ reach
> eth1 (which point to internal net) !!!
>
> The figure describe what's happen:
>
> ___________________
> | |
> | <- SYN |<- SYN <- SYN | |
> Target | |eth0 eth1 |----------| My box
> | SYN/ACK -> | -> | | telnet target 25
> |_____________ ____|
>
> ^
> |
> |_____ SYN/ACK never reach eth1 !!!
>
> The same thing occures when telneting Target on ports 7/9/79 etc...
>
> _But_ when I telnet Target 80 or 21 from My Box, it works !
> Why ?
> What am I missing ?
>
> I try with kernel 2.2.5, 2.2.12, 2.2.14.
>
> /proc/sys/net/ipv4/conf/{all,eth*}/rp_filter are set to 1
> /proc/sys/net/ipv4/ip_forward is set to 1
>
> Thanks in advance,
>
> -- Meir
> ps: thanks to cc to meir@education.gov.il
>
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This archive was generated by hypermail 2b29 : Thu Jun 15 2000 - 21:00:31 EST