Re: Ceph OSD network with IPv6 SLAAC networks?

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> Op 27 maart 2017 om 21:49 schreef Richard Hesse <richard.hesse@xxxxxxxxxx>:
> 
> 
> Has anyone run their Ceph OSD cluster network on IPv6 using SLAAC? I know
> that ceph supports IPv6, but I'm not sure how it would deal with the
> address rotation in SLAAC, permanent vs outgoing address, etc. It would be
> very nice for me, as I wouldn't have to run any kind of DHCP server or use
> static addressing -- just configure RA's and go.
> 

Yes, I do in many clusters. Works fine! SLAAC doesn't generate random addresses which change over time. That's a feature called 'Privacy Extensions' and is controlled on Linux by:

- net.ipv6.conf.all.use_tempaddr
- net.ipv6.conf.default.use_tempaddr
- net.ipv6.conf.X.use_tempaddr

Set this to 0 and the kernel will generate one address based on the MAC-Address (EUI64) of the interface. This address is stable and will not change.

I like this very much as I don't have any static or complex network configurations on the hosts. It moves the whole responsibility of networking and addresses to the network. A host just boots and obtains a IP.

The OSDs contact the MONs on boot and they will tell them their address. OSDs do not need a fixed address for Ceph.

However, using SLAAC without Privacy Extensions means that in practice the address will not change of a machine, so you don't need to worry about it that much.

The biggest system I have running this way is 400 nodes running IPv6-only. 10 racks, 40 nodes per rack. Each rack has a Top-of-Rack switch running in Layer 3 and a /64 is assigned per rack.

Layer 3 routing is used between the racks that based on the IPv6 address we can even determine in which rack the host/OSD is.

Layer 2 domains don't expand over racks which makes a rack a true failure domain in our case.

Wido

> On that note, does anyone have any experience with running ceph in a mixed
> v4 and v6 environment?
> 
> Thanks,
> -richard
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