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Simon Greenwood
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Adding an IPv6 default route with network-scripts in an EL8 server at OVH
Posted on Wed 06 September 2023 in Technical
This is a bit of a niche one, not least because network-scripts is supposed to be on its way out as a configuration method, despite cPanel still not supporting NetworkManager properly. No problem people, it's only been around for ten years.
This may also be specific to OVH's network, but I haven't found a resource that covers it, so here are my notes.
Dedicated servers at OVH are allocated a /64 IPV6 range. The gateway is the last address in the range, which is slightly more eye crossing than with IPV4, but ends in FF:FF:FF:FF. However, in EL8 (and in Debian-derived distros to my knowledge), ifup doesn't add a default gateway if it can't ping the address, and it can't ping the address because it needs a default gateway. This also applies to IPV4 in OVH's network, which is a pain for automatic provisioning.
The network-scripts system is remarkably flexible, and wrangling it is a dying art, but the key here is the ifup-post script. This runs after ifcfg-<device> and goes through a sequence of the other scripts in /etc/sysconfig/network-scripts- you can see which ones if you look at the code.
One of these is route6-<device> and this is where you add your default route so it's added after the initial network config. In OVH images it is disabled, and perhaps confusingly, includes a list of static routes generated by cloud-init. Rename that one, and using your editor of choice (vim, you animals), open a new file vi route6-eno1 (for example) and enter your gateway and default route like this:
2001:xxxx:xxxx:xxff:00ff:00ff:00ff:00ff dev eno1
default via 2001:xxxx:xxxx:xxff:00ff:00ff:00ff:00ff dev eno1
Enable the script by making it executable chmod +x route6-eno1.
and restart the network with systemctl restart network.
and you should now be able to ping the IPV6 host of your choice (let's face it, your local google.com gateway).
tech Enterprise Linux IPV6 Linux Networking
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