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I want to find the right iptables commands combination to address the following need:

  • NEs are NATed thru the linux box (using iptables) towards the WAN cloud, where the NTP servers are situated.
  • In order to achieve redundancy, the NTP Servers are in a load balancing cluster with one virtual IP address (172.30.4.245)
  • The problem is that when the NEs request for NTP updates using the 172.30.4.245, the NTP response is received from one of the actual IP addresses (.200, .230 .240).

Example:

The iptables is not allowing this flow, which is normal since the requested vs responding address are not the same (172.30.4.245 vs 172.30.4.230) :

Request : UDP 10.68.2.11:23445 ---> 172.30.4.245:123 (this is Before NAT, of course after NAT the source is 10.23.14.72) Response: UDP 172.30.4.230:123 ---> 10.23.14.72:23445 (Response to the WAN address)

I'm wondering if there is any way to let iptables establish the UDP flow only based on the (s-port/d-port) regardless of the IP addresses, and execute the NAT back to the LAN based on that.

UDP/NTP is just an example, almost all the needed services are setup in the same way (load balancing in Cluster).

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you could MASQUERADE both ways on your loadbalancers, but the suggestion below with something like ``ipvsadm` is a good one. –  Wrikken May 14 '13 at 19:42

1 Answer 1

Maybe you should look at your load balancer. Replacing a dumb NAT with something more sophisticated like IPVS should do the job.

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