I can't run SLAAC and DHCPv6 at the same time without giving devices multiple addresses, and Android doesn't support DHCPv6, so I'd have to carve out a separate, SLAAC-based, android-only network. And then figure out firewall rules, multicast reflection, etc.

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justincormack a day ago | parent | next [-]

Why is giving multiple addresses a problem?

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candiddevmike a day ago | parent [-]

No control over which source address is used. I'm assigning a lot of clients DHCP reservations so I can use static addresses for monitoring and firewall rules. With multiple addresses on the same network, clients may use their SLAAC address which won't match the firewall rule.

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db48x a day ago | parent | next [-]

That still doesn’t really make sense. Why not run SLAAC on one subnet and have a single firewall rule for the whole thing? You’re not running any major servers on an Android phone, so it won’t be anything complex.

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tsimionescu a day ago | parent [-]

SLAAC can only run on a subnet that's larger than /64, which they might not have access to.

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db48x a day ago | parent [-]

Strictly speaking it can and does run on subnets that are exactly /64. Does anyone actually hand out smaller delegations today?

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tsimionescu a day ago | parent [-]

My point is that they might only be getting 1 /64 from their ISP; or getting a /62 or something small, and needing more subnets anyway. In these situations, you may not have an extra /64 to dedicate to SLAAC for certain devices.

	▲	db48x a day ago \| parent [-]
		Right. I was merely correcting your statement that SLAAC needs more than 64 bits to work with. But my question remains; do any ISPs hand out smaller delegations than a /64?

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justincormack 21 hours ago | parent | prev | next [-]

There are APIs in Linux to control source address selection but might be fiddly https://www.davidc.net/networking/ipv6-source-address-select...

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franklyworks a day ago | parent | prev [-]

Ah, this makes sense.

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gspr a day ago | parent | prev [-]

I thought this was a problem too. Then I realized that addresses are not in short supply, so I stopped caring that some devices get multiple addresses. The ones I care about are handed out over DHCPv6, and the firewall works accordingly. The rest gets basic connectivity and nothing else.

Works great for me.

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candiddevmike a day ago | parent [-]

Don't you have problems with clients using the wrong source address and not matching firewall rules?

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kstrauser a day ago | parent | next [-]

Different person here, but no. I never write firewall rules based on individual source addresses. They’re too easy to fake. And with IPv6’s privacy extensions, you never know what source address a given machine will have anyway.

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gspr 21 hours ago | parent [-]

Interesting. How do you deal with destination addresses on your local network? DHCPv6 like the other poster and myself?

	▲	kstrauser 15 hours ago \| parent [-]
		I haven’t had a need for DHCPv6. I’d use DNS (or better, mDNS) to assign a hostname to the destination’s fixed IPv6 address or ULA, both of which are static. I don’t ever manually assign an IPv6 address to a host, though. I just let SLAAC do the thing it was designed for.

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gspr a day ago | parent | prev [-]

No. Admittedly, my firewall rules are all about granting something extra beyond the basics. I only do this for clients I care about anyway, so I can always tell them to use the right address.