Hello Nikolaus,
I have a doubt. It seems, rath of ebox is assigned with IP address in
the range 192.168.12.0/24. However, IP address of vostro seems to be
192.168.17.47 (assuming /24). Ebox doesn't have any route to this range.
So it try to use default route via eth0.
What I assume is, 'vostro' has IP addresses in (atleast) two ranges
(192.168.12.0/24, 192.168.17.0/24). In the default routing table, the
src IP is set to 192.168.12.x (for the packets originating from vostro).
However, the 'tovpn' table didn't specify the src IP. So, when the
'tovpn' table is being used, the packets may have got the src IP as
192.168.17.x.
I think, you can avoid this by explicitly specifying the src IP when
adding the route to 'tovpn' table,
ip route add default via 192.168.12.1 src 192.168.12.x table tovpn
Regards,
Vignesh
On 09/13/2013 10:40 AM, Nikolaus Rath wrote:
Hello,
Thanks for working on this great networking stack!
I'm trying to set up a configuration with SNAT and routing rules, but
I'm having weird problems that I do not understand:
I've enabled packet forwarding and SNAT on the "ebox" computer as
follows:
root@ebox:~# ip route
default via 23.92.25.1 dev eth0
23.92.25.0/24 dev eth0 proto kernel scope link src 23.92.25.96
192.168.12.0/24 dev rath proto kernel scope link src 192.168.12.1
root@ebox:~# iptables -L -n -v
Chain INPUT (policy ACCEPT 1314 packets, 1736K bytes)
pkts bytes target prot opt in out source destination
Chain FORWARD (policy DROP 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
150K 62M ACCEPT all -- rath eth0 0.0.0.0/0 0.0.0.0/0
86746 200M ACCEPT all -- eth0 rath 0.0.0.0/0 0.0.0.0/0 state RELATED,ESTABLISHED
319 22076 LOG all -- * * 0.0.0.0/0 0.0.0.0/0 limit: avg 1/min burst 30 LOG flags 0 level 4 prefix "Rejected forwarding: "
393 26172 REJECT all -- * * 0.0.0.0/0 0.0.0.0/0 reject-with icmp-net-prohibited
Chain OUTPUT (policy ACCEPT 1142 packets, 2412K bytes)
pkts bytes target prot opt in out source destination
root@ebox:~# iptables -t nat -L -n -v
Chain PREROUTING (policy ACCEPT 36378 packets, 2383K bytes)
Chain INPUT (policy ACCEPT 19982 packets, 1334K bytes)
pkts bytes target prot opt in out source destination
Chain OUTPUT (policy ACCEPT 61430 packets, 4601K bytes)
pkts bytes target prot opt in out source destination
Chain POSTROUTING (policy ACCEPT 8333 packets, 564K bytes)
pkts bytes target prot opt in out source destination
69488 5081K SNAT all -- * eth0 0.0.0.0/0 0.0.0.0/0 to:23.92.25.96
>From a second computer "vostro", I can now use ebox as a gateway:
root@vostro:~# ip route add 190.93.249.164 via 192.168.12.1
This works fine, now connections to whatismyip.com (190.93.249.164) go
through ebox.
However, when I try to be a bit more selective on vostro and use a
special routing table, things don't work anymore:
root@vostro:~# iptables -t mangle -L -n
Chain PREROUTING (policy ACCEPT)
target prot opt source destination
Chain INPUT (policy ACCEPT)
target prot opt source destination
Chain FORWARD (policy ACCEPT)
target prot opt source destination
Chain OUTPUT (policy ACCEPT)
target prot opt source destination
MARK tcp -- 0.0.0.0/0 190.93.249.164 tcp dpt:80 MARK set 0x1
LOG tcp -- 0.0.0.0/0 190.93.249.164 tcp dpt:80 LOG flags 0 level 4 prefix "marked: "
Chain POSTROUTING (policy ACCEPT)
target prot opt source destination
root@vostro:~# ip route del 190.93.249.164 via 192.168.12.1
root@vostro:~# ip route add default via 192.168.12.1 table tovpn
root@vostro:~# ip rule add fwmark 0x1 table tovpn
Now connections from vostro to 190.93.249.164 still make it to ebox, and
from ebox to 190.93.249.164, but the answers get stuck on ebox:
Sep 13 04:47:53 ebox kernel: Rejected forwarding: IN=eth0 OUT=eth0 MAC=f2:3c:91:69:db:07:84:78:ac:0d:79:c1:08:00 SRC=190.93.249.164 DST=192.168.17.47 LEN=60 TOS=0x00 PREC=0x00 TTL=58 ID=0 DF PROTO=TCP SPT=80 DPT=39024 WINDOW=14480 RES=0x00 ACK SYN URGP=0
It seems that ebox tries to send the packet destined to go trough the
rath to eth0 instead, and consequency rejects them because forwarding is
only enabled from eth0 to rath.
However, this only happens when vostro has the gateway route set in a
special routing table rather than the default table -- but how does ebox
even know about that?
Can someone explain to me what is happening here and why?
Best,
-Nikolaus
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