$ curl -insecure -header 'Host: Notice that we manually sent the ‘Host’ header to make up for the fact that we are sending the $myhttpserver $ echo going to use $myhttpserver as my http server $ myntpserver=$(nslookup 0. | grep -i Address | tail -n 1 | awk ) You can verify the basic functionality by pulling a single IP out of this load balanced name, and then checking the network time using the ntp client. Then validate the changes are in effect: $ sysctl _forwardįor the UDP example, we will use a public network time protocol (NTP) server that is known to listen on port 123/udp, “0.”. If it is not, then set the value immediately and persistently in the nf file. Prerequisitesīefore we can start modifying iptables, IP forwarding must be enabled on “proxyVM”. But other than the naming convention, this iptables forwarding solution would work the same on either version.

On an older version of Ubuntu, they would have been named “eth0” and “eth1”. The reason why proxyVM has ethernet interfaces named “enpos3” and “enp0s9” is because it is an Ubuntu 16.04 xenial host that incorporates systemd’s predictable network interface name scheme. The external services will have no idea they are actually serving a request originating from privateVM1 (and will believe they are simply talking to proxyVM). PrivateVM1 will only make calls to proxyVM (and will have no knowledge of the outside world). To reach critical external services, they rely upon a host named “proxyVM” that has an interface on the 172.28.128.0 network, but has an additional interface in the 192.168.2.0/24 network that allows it to reach external networks. “privateVM1” (as well as all the other VMs in that network) are segmented and isolated in the 172.28.128.0/24 network. In this article, I will show you how to use iptables to forward tcp and udp port requests from one private network to another using a single bridging host (port f0rwarding).įor this exercise, we will use the network shown below. Having a single host act as the access point to an outside service allows you to keep your internal hosts isolated in their own private network, using NAT to transparently forward the request and route back the responses. Having hosts in your private networks use a single access point to services in the outside world institutes the type of control often required in production data centers. In previous articles I have described how to use a Squid proxy as a bridge to outside services such as http and ftp.

Ubuntu iptables