I'm replacing a CentOS server with an Ubuntu 20 one. I need to duplicate the older servers routing configuration. The outputs of "ip route show" and "route" are not directly usable as inputs.

I'm a bit reluctant to hand-translate the output into route commands, because errors always creep in. Is there a better way?

`route` shows the current routing tables as a table with these columns:
Destination,Gateway,Genmask,Flags,Metric,Ref,Use,Iface

So I saved that output to a file, and copied it to the new host. I converted the raw output to a csv file by removing the first line, replacing the spaces with a comma. I also replaced the device names with ones that matched on the new system. So sample data might look like this:

Destination,Gateway,Genmask,Flags,Metric,Ref,Use,Iface
default,gateway,0.0.0.0,UG,0,0,0,enp5s0
default,toblerone.mydomain.org,0.0.0.0,UG,100,0,0,eno1
192.168.0.0,0.0.0.0,255.255.255.0,U,100,0,0,eno1
192.168.1.0,0.0.0.0,255.255.255.0,U,0,0,0,enp5s0
192.168.1.0,gateway,255.255.255.0,UG,0,0,0,enp5s0

The `route` command can produce unexpected errors when the rout already exists. I also don't want the generated commands to run directly. So my PowerShell script looks like this:

#!/usr/bin/env pwsh

Set-StrictMode -Version Latest

$ErrorActionPreference = "Stop"
$PSDefaultParameterValues['Set-*:ErrorAction'] = "Stop"

$routeDataCSV = Import-CSV "./route_data.csv"
# A route should only be deleted once per run.
$routeDeleted = @{}

foreach ($routeIn in $routeDataCSV) {
if (!$routeDeleted[$routeIn.Destination] -or (!($routeDeleted[$routeIn.Destination] -like "true"))) {
Write-Output "route del -net $($routeIn.Destination)"
$routeDeleted[$routeIn.Destination] = "true"
}
Write-Output "route add -net $($routeIn.Destination) gw $($routeIn.Gateway) netmask $($routeIn.Genmask) metric $($routeIn.Metric) dev $($routeIn.Iface)"
}

The generated commands are then:

route del -net default
route add -net default gw gateway netmask 0.0.0.0 metric 0 dev enp5s0
route add -net default gw toblerone.mydomain.org netmask 0.0.0.0 metric 100 dev eno1
route del -net 192.168.0.0
route add -net 192.168.0.0 gw 0.0.0.0 netmask 255.255.255.0 metric 100 dev eno1
route del -net 192.168.1.0
route add -net 192.168.1.0 gw 0.0.0.0 netmask 255.255.255.0 metric 0 dev enp5s0
route add -net 192.168.1.0 gw gateway netmask 255.255.255.0 metric 0 dev enp5s0

`ip route show` shows each route entry in the main table exactly as it can be used as input to 'ip route add' ... so just prefix each line in the output with with 'ip route add ', e.g. like this:

the output of the above can be executed exactly as is in any shell
(but of course you need to change ifc names if they are changed on your new setup)

1 members found this post helpful.

Why not look at the network setup scripts on Centos and translate to netplan? It is almost 1-1 setup.