Hello Herbert and Enrico
There is a problem with UDP port forwarding from a host doing NAT into vservers which have multiple ip adresses. Depending on the order how the ip addresses are fed to chbind, the forwarding will work or not. TCP port forwarding is not affected.
Steps to reproduce:
You need two machines,
[H]= vserver- and NAT-enabled host (I'm using 2.4.27 and vs1.3.9) with
netcat.
[R]= remote host; no vserver needed, with netcat.Setup on [H]:
(no vservers running and no active iptables rules)
ifconfig eth0 1.2.3.4
ifconfig lo 127.0.0.1
ifconfig lo:1loc 10.0.0.1 up
ifconfig lo:1pub 192.168.0.1 up
iptables -t nat -A PREROUTING -i eth0 -d 1.2.3.4 -p udp --dport 666 -j DNAT --to 192.168.0.1
Then:
Test 1: getting in touch with the problem:
on.. type this..
[H] netcat -n -l -u -v -p 666
[R] netcat -n -u 1.2.3.4 666
bla1
bla2
(type two lines of text; the first is getting through to [H], the
second not - netcat terminates, since a "port unreachable" packet is
sent back from H to R upon receiving the second packet.)This test just shows that the kernel can behave somewhat strange if the listener binds to * (0.0.0.0) when a NAT rule is forwarding to a second address - looks like the kernel is getting confused somehow. This happens also on a vanilla 2.4.27 kernel.
Test 2: making the problem disappear using -s flag:
[H] netcat -n -l -u -v -p 666 -s 192.168.0.1
[R] netcat -n -u 1.2.3.4 666
bla1
bla2
bla3
...
You can type as many lines you want, it's all getting through, and any
typing on H is sent to R.
"Kernel is somehow not confused anymore", since netcat is listening
only on the target ip of the DNAT rule.Test 3: making the problem disappear using chbind: [H] chbind --ip 192.168.0.1 netcat -n -l -u -v -p 666 [R] (same as above)
The effect is the same as with test 2.
Test 4: making the problem appear again:
[H] chbind --ip 10.0.0.1 --ip 192.168.0.1 netcat -n -l -u -v -p 666
[R] netcat -n -u 1.2.3.4 666
bla1
bla2
(netcat stops again)Test 5: and making it disappear again: [H] chbind --ip 192.168.0.1 --ip 10.0.0.1 netcat -n -l -u -v -p 666 [R] (as always) Note the reversed order of the ip's. Connection works again correctly.
So, the net effect is: If you configure your vservers to use two ip's (for example: one for "localhost" purposes, and a second for public access), and use UDP port forwarding from the NAT'ing host, and be so unlucky that the order how the two ip's are fed to chbind during the vserver startup is that the first ip is *not* the target ip of the forwarding, you're 'sol'. If the utils (I'm currently using alpha utils 0.29.211) would provide a way to tell the order of the ip's, one could at least work around the problem once being aware of it.
BTW it does not matter whether you additionally have SNAT rules for outgoing traffic or not.
Cheers Christian. _______________________________________________ Vserver mailing list [EMAIL PROTECTED] http://list.linux-vserver.org/mailman/listinfo/vserver
