0

In a LAN environment, I have 3 exchange servers that have been deployed for high availability and failover in case one of the 3 servers becomes unavailable.

Currently, my NAT settings only send packets to the first server. I would like the ability to have emails (packets) sent on the network to servers 2 and 3 as well in the case that any of the three become unavailable.

How should I do this on my Cisco router?

Currently, I have NAT setting

ip nat inside source static tcp 10.200.15.33 25 96.92.221.221 25 extendable ip nat inside source static tcp 10.200.15.33 110 96.92.221.221 25 extendable etc..

Kevin
  • 1

1 Answers1

0

You can use inside destination NAT instead of inside source NAT to set up a pool of inside addresses, which can be used in a rotary fashion:

Destination Address Rotary Translation

A dynamic form of destination translation can be configured for some outside-to-inside traffic. Once a mapping is set up, a destination address matching one of those on an access list will be replaced with an address from a rotary pool. Allocation is done in a round-robin basis, performed only when a new connection is opened from the outside to the inside. All non-TCP traffic is passed untranslated (unless other translations are in effect). This feature was designed to provide protocol translation load distribution. It is not designed nor intended to be used as a substitute technology for Cisco's LocalDirector product. Destination address rotary translation should not be used to provide web service load balancing because, like vanilla DNS, it knows nothing about service availability. As a result, if a web server were to become offline, the destination address rotary translation feature would continue to send requests to the downed server.

ip nat inside destination { list <acl> pool <name> | static <global-ip> <local-ip> }

This command is similar to the source translation command. For dynamic destination translation to make any sense, the pool should be a rotary-type pool.

Ron Maupin
  • 3,243
  • 1
  • 12
  • 20
  • Would this kind of setup be favorable and appropriate for Exchange? My concern is how each of the exchange servers would handle a situation where an identical piece of email was received on each of the three servers (due to the network setup). – Kevin May 17 '16 at 00:28
  • The traffic isn't sent to all three servers. A single flow will be sent to only one server, but each server will get a new flow in turn. I really can't comment on how suitable it is for an Exchange server. Your only other option is to put in a load balancer behind the router, and NAT to it. A dedicated load balancer is suitable for all types of traffic, but it probably costs more than your router did. – Ron Maupin May 17 '16 at 00:31