Round robin load balance to local port range

Hi all,

I'm trying to load balance (round robin) to multiple instances of openvpn running locally in ports 9000-9004 without luck.

2.6.30.9-96.fc11 / iptables-1.4.3.1-1.fc11

For testing I tried first on the output chain to see if it works.

iptables -t nat -A OUTPUT -d 127.0.0.1 -m tcp -p tcp --dport 8000 -j DNAT --to-destination :9000-9004 iptables -t filter -I INPUT 1 -m tcp -p tcp --dport 9000:9004 -j LOG

telnet 127.0.0.1 8000
telnet 127.0.0.1 8000
telnet 127.0.0.1 8000

Nov  6 17:27:20 localhost kernel: IN=lo OUT= MAC=00:00:00:00:00:00:00:00:00:00:00:00:08:00 SRC=127.0.0.1 DST=127.0.0.1 LEN=60 TOS=0x10 PREC=0x00 TTL=64 ID=37697 DF PROTO=TCP SPT=35462 DPT=9000 WINDOW=32792 RES=0x00 SYN URGP=0
Nov  6 17:27:21 localhost kernel: IN=lo OUT= MAC=00:00:00:00:00:00:00:00:00:00:00:00:08:00 SRC=127.0.0.1 DST=127.0.0.1 LEN=60 TOS=0x10 PREC=0x00 TTL=64 ID=30693 DF PROTO=TCP SPT=35463 DPT=9000 WINDOW=32792 RES=0x00 SYN URGP=0
Nov  6 17:27:22 localhost kernel: IN=lo OUT= MAC=00:00:00:00:00:00:00:00:00:00:00:00:08:00 SRC=127.0.0.1 DST=127.0.0.1 LEN=60 TOS=0x10 PREC=0x00 TTL=64 ID=12621 DF PROTO=TCP SPT=35464 DPT=9000 WINDOW=32792 RES=0x00 SYN URGP=0

As you can see all connections are natted but only port 9000 is being used from the range.

I also tried with redirect
iptables -t nat -A OUTPUT -d 127.0.0.1 -m tcp -p tcp --dport 8000 -j REDIRECT --to-ports 9000-9004 or even
iptables -t nat -A OUTPUT -d 127.0.0.1 -m tcp -p tcp --dport 8000 -j DNAT --to-destination 127.0.0.1:9000-9004

same results, only port 9000.

According to the man page:

In Kernels up to 2.6.10 you can add several --to-destination
options. For those kernels, if you specify more than one
desti-
nation address, either via an address range or
multiple
--to-destination options, a simple round-robin
(one after
another in cycle) load balancing takes place
between these
addresses. Later Kernels (>= 2.6.11-rc1) don¢t have the
ability
to NAT to multiple ranges anymore.

Either the kernel is doing some kind of hashing based on my src-ip instead of round-robin or the last phrase should change "to ranges anymore" instead of "multiple ranges anymore"

I'm using a single range (ports 9000-9004) thus not multiple ranges.

Am I doing something wrong here or is it something I don't get?

best regards,

Giannis

The manpage is incorrect (patches welcome :), it will use the first port as long as the tuples don't clash. The --random option can be used to randomly select a port from the range.

--random does the job both for DNAT and REDIRECT
I guess random is better that nothing :)

Just for clarification: the state of the packet will be remembered right? I don't want to send it first to one port and later to another.

regards and thanks for the quick answer

Giannis

ps. I found another bug
--random in DNAT has to be put at the end of the rule otherwise if you put it before --to-destination
error: "Multiple --to-destination not supported"

Correct.

Thanks, fixed in git.