Hello,
I have some problems testing local interfaces over loopback.
Consider the following setup:
if0: 10.1.1.1 pointopoint 10.1.1.12
if1: 10.1.1.2 pointopoint 10.1.1.11
cable connects if0 with if1
iptables -A POSTROUTING -t nat -d 10.1.1.11 -j SNAT --to 10.1.1.12
iptables -A POSTROUTING -t nat -d 10.1.1.12 -j SNAT --to 10.1.1.11
iptables -A PREROUTING -t nat -d 10.1.1.11 -j DNAT --to 10.1.1.1
iptables -A PREROUTING -t nat -d 10.1.1.12 -j DNAT --to 10.1.1.2
ping 10.1.1.11 and ping 10.1.1.12 work as expected
Here's what I believe is going on:
ping 10.1.1.11
src dst
10.1.1.2 10.1.1.11
POSTROUTING(if1)
10.1.1.12 10.1.1.11
OUT: if1
IN: if0
10.1.1.12 10.1.1.11
PREROUTING(if0)
10.1.1.12 10.1.1.1
ICMP
10.1.1.1 10.1.1.12
POSTROUTING(if0)
10.1.1.11 10.1.1.12
OUT: if0
IN: if1
10.1.1.11 10.1.1.12
PREROUTING(if1)
10.1.1.11 10.1.1.2
ping response from 10.1.1.2
Now the setup which I cannot make to work:
if0: 10.1.1.1 pointopoint 10.1.1.12
if1: 10.1.1.3 pointopoint 10.1.1.14
if2: 10.1.1.4 pointopoint 10.1.1.13
if3: 10.1.1.2 pointopoint 10.1.1.11
cables connect if0 to if1 and if2 to if3
iptables -A POSTROUTING -t nat -d 10.1.1.11 -j SNAT --to 10.1.1.3
iptables -A POSTROUTING -t nat -d 10.1.1.12 -j SNAT --to 10.1.1.4
iptables -A POSTROUTING -t nat -d 10.1.1.13 -j SNAT --to 10.1.1.11
iptables -A POSTROUTING -t nat -d 10.1.1.14 -j SNAT --to 10.1.1.12
iptables -A PREROUTING -t nat -d 10.1.1.11 -j DNAT --to 10.1.1.14
iptables -A PREROUTING -t nat -d 10.1.1.12 -j DNAT --to 10.1.1.13
iptables -A PREROUTING -t nat -d 10.1.1.13 -j DNAT --to 10.1.1.2
iptables -A PREROUTING -t nat -d 10.1.1.14 -j DNAT --to 10.1.1.1
ping 10.1.1.1 and ping 10.1.1.2 don't work
Here's what I believe should be going on (but apparently it isn't):
ping 10.1.1.11
src dst
10.1.1.2 10.1.1.11
POSTROUTING(if3)
10.1.1.3 10.1.1.11
OUT: if3
IN: if2
10.1.1.3 10.1.1.11
PREROUTING(if2)
10.1.1.3 10.1.1.14 (FWD)
POSTROUTING(if1)
10.1.1.12 10.1.1.14
OUT: if1
IN: if0
10.1.1.12 10.1.1.14
PREROUTING(if0)
10.1.1.12 10.1.1.1
ICMP
10.1.1.1 10.1.1.12
POSTROUTING(if0)
10.1.1.4 10.1.1.12
OUT:if0
IN:if1
10.1.1.4 10.1.1.12
PREROUTING(if1)
10.1.1.4 10.1.1.13 (FWD)
POSTROUTING(if2)
10.1.1.11 10.1.1.13
OUT:if2
IN:if3
10.1.1.11 10.1.1.13
PREROUTING(if3)
10.1.1.11 10.1.1.2
ping response from 10.1.1.2
Any ideas why it doesn't work (I enabled ip_forward and disabled
rp_filter)?
And is it posible to blindly forward packets from if1/if2 to if2/if1
(since the devices are not ehernet I think ethernet bridging does not
qualify)?
Thanks,
Jarek Sobieszek
