Thursday, May 28, 2020

Static route on dual homed vSphere Replication appliance

Recently went through the process of upgrading and troubleshooting a vSphere Replication environment. What was particular about that environment is the vSphere Replication appliances had 2 network interfaces.

The first interface (eth0) has the default gateway, but it is not used for replication traffic. The second interface (eth1) is connected to the portgroup that also connects to ESXi replication vmkernel portgroup. So, replication traffic is supposed to go over eth1. Main site and DR site have networks from different subnets, but connectivity is possible over the replication network. Since hosts in protected site (main site) need to communicate to vSphere Replication server  in DR site we need to force this communication to go over the replication network.

The solution is pretty simple, add a static routes on the appliances to reach the opposite site over the replication network as following:

route add -net gw

The route is not persistent and it will be lost upon reboot. To make it persistent, we need to add it to a configuration file. vSphere Replication 8.1 and 8.2 are running on VMware Photon OS 2.0. Normally you add the static route in the configuration file for the network where you want to have it. In my case in /etc/systemd/network/



However this did not work and the route was not picked up at reboot. Then I tried a different approach. I needed to be sure the route add command would be run every time the appliance restarts, so I added it as a service. I first created the service configuration file called staticroute.service ( a name of my choice). The file is created in /lib/systemd/system/ and contains the following:

Description=Add static route for eth1

ExecStart=/usr/sbin/route add -net gw


Finally I've created a symbolic link for the file:

cd /lib/systemd/system/
ln -s ../staticroute.service staticroute.service

Once you do that you can run ls -la to display the files and you will see your staticroute.service

This will ensure the static route is created at every reboot. Make sure to add the routes in both sites. To test the communication you only need to traceroute the ESXi host replication IP from the opposite site.

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