TCP RSTs seen when routing is expected.

Scott Edwards supadupa at gmail.com
Sun May 17 03:40:03 MDT 2009


I'm expecting this box to forward traffic like a router, but it's not
playing nice.  It might be because I'm up at 3:30am trying to figure
this out. hah :)  the 192.0.0.2 address is simply for "example.com"
style usage.

forwarding was enabled by echo 1 > /proc/sys/net/ipv4/ip_forward

iptables-save shows all chains are ACCEPT.  There is one rule in the
nat table, FOWARD chain, as ACCEPT, however there are no packets/bytes
accounted for.

joe:~# iptables-save -c
# Generated by iptables-save v1.3.6 on Sun May 17 05:30:45 2009
*raw
:PREROUTING ACCEPT [577431792:362231328154]
:OUTPUT ACCEPT [728727849:796223845493]
COMMIT
# Completed on Sun May 17 05:30:45 2009
# Generated by iptables-save v1.3.6 on Sun May 17 05:30:45 2009
*nat
:PREROUTING ACCEPT [9039298:481968201]
:POSTROUTING ACCEPT [8247008:528498550]
:OUTPUT ACCEPT [8244338:528359281]
COMMIT
# Completed on Sun May 17 05:30:45 2009
# Generated by iptables-save v1.3.6 on Sun May 17 05:30:45 2009
*mangle
:PREROUTING ACCEPT [577431792:362231328154]
:INPUT ACCEPT [577418236:362230055052]
:FORWARD ACCEPT [13212:1256264]
:OUTPUT ACCEPT [729094611:796543310780]
:POSTROUTING ACCEPT [730008665:796516451576]
COMMIT
# Completed on Sun May 17 05:30:45 2009
# Generated by iptables-save v1.3.6 on Sun May 17 05:30:45 2009
*filter
:INPUT ACCEPT [577418225:362230054083]
:FORWARD ACCEPT [13212:1256264]
:OUTPUT ACCEPT [728727348:796223813446]
[0:0] -A FORWARD -d 192.0.0.5 -j ACCEPT
COMMIT
# Completed on Sun May 17 05:30:45 2009
joe:~# cat /proc/sys/net/ipv4/ip_forward
1

With, tcpdump -eni ethX host 192.0.0.5, when TCP traffic is destined
to us, I expect it to forward this to the destination.  However, it's
creating TCP RST's.  Not even icmp host unreachable etc.

anything else I should look at? (except a good nights rest?)

Scott.



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