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Casper
Asked: 2018-09-14 20:00:01 +0800 CST

Linux - how to set a default route with 0.0.0.0 as gateway

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I have a problem where I need to manually set up a route on Ubuntu 18.04 during the init (ram) process. I cannot use any of the new networking tools, only Busybox is available.

The routing table should looks like this:

Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
0.0.0.0         172.31.1.1      0.0.0.0         UG    100    0        0 ens3
172.31.1.1      0.0.0.0         255.255.255.255 UH    100    0        0 ens3

The host is a VPS with an IP of 95.xx.xx.xx, so the gateway IP is not on the same network. I can't figure out what command to build the above table with. I get various SIOCADDDRT errors with everything I try.

Here's what I've tried so far:

> route add default gw 172.31.1.1
SIOCADDDRT: Network uncreachable
> route add default gw 172.31.1.1 via 0.0.0.0 
..invalid format
> route add 172.31.1.1 gw 0.0.0.0
SIOCADDDRT: Invalid argument
> route add 0.0.0.0 gw 172.31.1.1
SIOCADDDRT: Network uncreachable
> route add default gw 0.0.0.0
SIOCADDDRT: Invalid argument

Is there any way to make this work with Busybox? Or any other way to make it happen inside initram?

linux

1 Answers

  1. Best Answer

    On your desired output in flags, 'G' indicates a gateway, and 'H' represents a host. Hence for the 0.0.0.0 output you are trying to create for the route, its not really used.

    To add a host IP to the interface that will generate the same output:

    ip addr add 172.31.1.1/32 dev ens3
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