Monday, April 25, 2016

systemd: Ubuntu 16.04 better, not best

by Craig Miller


Sure other Linux distributions have already released versions with systemd. But just last week, Ubuntu, one of the most popular distros released XenialXerus aka 16.04 LTS with systemd integrated. Actually Canonical has been phasing in pieces of systemd for some time. But with the release of 16.04 LTS, the networking component (systemd-networkd) has been enabled.

A quick look of the new releases reveals that Canonical has been following the evolution of systemd, and made sure they had a recent version (229). That is only one behind the current version of 230. Considering they did a code freeze two months ago, that is pretty good.

What IPv6 issues remain for this long term release of Ubuntu?

Referring to the list from systemd: oh, you wanted to run IPv6? post, the folks at Canonical have fixed:
  • Temporary addresses (RFC 4941) are broken from version 224 to 228 (systemdissue#2242) this was actually fixed in v229, and I suspect this is why Ubuntu went with v229.
  • Interface disable/enable IPv4 will reaquire and address, but IPv6 will not (other than link-local), and will remain address-less until restarting networkd (systemd issue #2912)
  • SLAAC address does not conform to RFC 4862, using EUI-64 (fixed in version 230)

What is NOT fixed?
  • IPv6 RA flood (THC flood_router6) causes network disconnection even after flood ceases (systemd issue#2977)
The behaviour of the RA flood is better than the current version 230, as Ubuntu server isn't disconnected, but the route table is flooded, and the "real" default route is lost, causing the server to lose IPv6 connectivity to anything off-net (like the internet). Even after the RA flood is stopped, and real RAs are heard from the real router, the default route is not inserted, and the server remains crippled. The only method to recover, is to reboot the server. Not the nicest thing to do, especially if the server is in production.

I haven't tested the virtualization issues, but I am hopeful that they have been improved by Canonical as well.

So where does this leave us?

I stand by my recommendation. systemd, and specifically systemd-networkd is not ready for IPv6 production systems. That said, it is certainly good enough for testing and development systems, giving you valuable experience towards your IPv6 deployment.



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