SLAAC versus DHCPv6

eagle61

Just remember that DHCPv6 uses DUID for assigning the IPv6 address not the MAC address

It depends on the OS. Debian (12) Server still generates the IPv6-Adress based on MAC-Address. First /64 based on IPv6-Prefix, the last /64 on the MAC

Example:
inet6 XXXX:XXXX:XXXX:XXXX:5052:11ff:fe98:bb16
MAC 52:52:11:98:bb:16
The ff:fe is always same added to the middle part
So if you know that ff:fe is always same you know the MAC-Address by recording the IPv6-Adress.This is default using network/interfaces in auto or dhcp6 mode for ipv6

Using Ubuntu-Server instead of Debian it might be different and it may use the DUID since Ubuntu-Server uses not network Interfaces but Netplan. Since i never use any Windows no idea what this OS do or not. Its anyway the most worthless OS ever

Jung-Fernmelder

@eagle61 said in SLAAC versus DHCPv6:

Debian (12) Server

Is there a special release of Debian for servers? I just use Debian stable for both servers and personal computers. It's the best operating system I've ever used, much better than any release of Windows.

@eagle61 said in SLAAC versus DHCPv6:

Debian (12) Server still generates the IPv6-Adress based on MAC-Address

Privacy extensions can be enabled by editing the /etc/network/interfaces if needed. I think that you can add "privext 2" to the according interface.

eagle61

@Jung-Fernmelder said in SLAAC versus DHCPv6:

Is there a special release of Debian for servers?

Not a special release of Debian for servers, but deffrent option to install Debian. If you choose in the installation Routine to install Debian as Server you will have /network/interface as tool to manage your Networtk-Connections
If you choose in the installation Routine to install Debian with full Desktop (ie XFCE, KDE, Gnome) then it will not only install much more packages out of the box, like LibreOffice, Firefox and such, but also Network Manager to manage your Networtk-Connections.

I do use Debian only as Server OS, so in Server Mode.
As OS on Notebooks i do use Ubuntu instead. Ubuntu also use Network Manager to manage your Networtk-Connections if installed with full Desktop (in my case XFCE).
The behavior of Network Manager, Netplan and /etc/Network/interfaces regarding IPv6 are by default different, not same. That's why i mentioned the Installation as Sever to make sure its not a desktop installation with different behavior.

But for the Network Interface of my pfsense i use to connect Devices via WIFI i do not use DHCPv6-Server but SLAAC (Router Advise = Unmanaged) only, since i also use Android devices to connect there. On the Network Interface of my pfsense i use to connect my Debian-Server i do use DHCPv6-Server not SLAAC (Router Advise = Managed).
The reason is one of the Debian Server is a server with a Nextcloud i want to reach via IPv6 from all over the Internet.
Since my ISP forces every 24 hours a reconnect i get every 24 hours a new IPv6-Prefix. So i use pfsenses KEA IPv6-Server and a DYNdns-Service to manage that resulting every 24 hour change of IPv6-Adress.

Privacy extensions can be enabled by editing the /etc/network/interfaces if needed.

Yes, but in case of a server that shall be reached from Internet that does not make much sense.I keep the last /64 of the IPv6-Adress static and KEA manage to change the prefix only after the 24 hours reconnect. So i can use on side of the DYNdns-Service Provider the to manage the AAAA-Record the Format: "Interface-ID" (ex. ::6743:12::f9aa::44a1) and the DYNdns-Service Provider just receives from pfsense the changed Prefix to create the full new IPv6-Adress every 24 hours of the Nextcloud. This would also work with Format: "EUI-64 MAC" (ex. 3C:49:37:12:26:B3) if MAC is used not DUID

tibere86

I have debated SLAAC vs. DHCPv6 myself. At the end, I prefer SLAAC as it's "hands off" easy management.

The issue I have ran into is with RA. When I enable SLAAC (fully disable DHCPv6) and set the router priority to HIGH and advertise my Pihole instance for IPv4 + IPv6 DNS server, the Pihole instance gets inundated with new IPv6 clients to the point of where there will be thousands of clients registered in Pihole, bogging it down, even though there are only ~30 devices on my network. Is this due to the SLAAC privacy IP rotation?

I have never been able to solve this. I have no issues when I leave RA DNS servers as default (router).

keyser

@Jung-Fernmelder Honestly, IPv6 client side is just not industry mature yet. It works fine - if you can control everything on the clients, but there are WAY to many options/standards or OS/vendor specific issues to make IPv6 really easy to use AND manage.

It’s a pita that they cock’ed up IPv6 so much. There was a lot of potential in IPv6 before all the petty squables and lack of unified standards broke everything.

As long as an IPv4 address is required to reach all corners of the Internet, just disable IPv6, and make your life A LOT easier.

ronv42

I think the real issue is that for consumers SLAAC was supposed to make provisioning of single segment home networks "just work". But then ISP's being the center of all control didn't follow the outlined best practice that a /54 or /60 is the base prefix and allowing the IPv6 addresses to be "persistent". Too many ISP's only will issue a /64 for one segment, expire the address every 24 hours forcing the network and devices to re-address each time.

If things were different, I would have engineered IPv6 internet where I pay per year for a block of IPv6 addresses /54 and that would be portable to any ISP and the ISP just becomes a pipe. The ISP shouldn't have the power to revoke address's based on a policy that blows in the wind.

One the client side there would be only two rules SLAAC or DHCPv6 assisted by SLAAC for router and DNS information for static addressing.

JKnott

@keyser said in SLAAC versus DHCPv6:

It’s a pita that they cock’ed up IPv6 so much.

No. It was Google that didn't enable DHCPv6 on Android or Chrome devices.

keyser

@JKnott said in SLAAC versus DHCPv6:

No. It was Google that didn't enable DHCPv6 on Android or Chrome devices.

It’s a little more complicated than that - I have yet to successfully directly attach pfSense to an ISP and have IPv6 working (tried 4 different ISPs that all “supports” IPv6 now). If you set it up behind the ISPs router where they have made sure basic Windows/Linux clients work, then pfSense will also work. But anything directly linked to the ISP fiber/bridgemode box is a PITA to get IPv6 working properly.

The problems comes from the MILLIONS of options both the SLAAC and the DHCP 6 proces offers, and if the client does not send the right parameters, use the correct intervals or accepts persistence, something/everything IPv6 related stops working.
On top of that the DHCP6c Client in pfSense doesn’t support many of the DHCPv6 options that I have seen ISP’s require to get IPv6 going - Or it doesn’t support the specific combo of settings/intervals needed to keep it going after the intial lease is accepted.

Granted - this is mainly the ISPs that are cock’ing up things, but the fact that it CAN require so much special config with very specific settings and configurations to get basic DHCPv6 going just shows it’s not matured yet (or standardized properly)

Patch

@ronv42 said in SLAAC versus DHCPv6:

Too many ISP's only will issue a /64 for one segment, expire the address every 24 hours forcing the network and devices to re-address each time.

If things were different, I would have engineered IPv6 internet where I pay per year for a block of IPv6 addresses /54

You are describing the difference between a static and dynamic IP address.

Static is better for a public or at least internet accessible server (dynamic Domain name not required)
Dynamic is better for user privacy (IP with mask shows ISP user has used to access internet rather than which user internet account was used).

JKnott

@Patch said in SLAAC versus DHCPv6:

You are describing the difference between a static and dynamic IP address.

If the ISP honours the DUID the prefix should be essentially static. I've had the same prefix for well over 5 years. That's "static" enough for me.

Patch

@JKnott
Not sure why that was addressed to me. I was describing the different use case for static and dynamic IP, not how to get a static IP.

JKnott

@Patch

Well, I did respond to your post. However, the last line about dynamic is better for privacy is wrong. With SLAAC you get up to 7 privacy addresses, based on a random number. You get a new one every day, with the oldest falling off the list. The most recent is the address used for outgoing connections. The consistent address, which can be based on either the MAC address or a random number, can be used for things like VPN access to your network. Unless the DHCPv6 address changes every day, it's actually worse for privacy.

ronv42

@JKnott I don't know if you have Comcast or not. I am fighting them for a site I just hooked up in Northbrook, Illinois. Every 24 hours they re-allocate the darn IPv6. They are handing out a /60 but it's a PITA I will be removing their Xfinity gateway and going with a vanilla cable modem and seeing if this gets rid of the IP address swaps they are doing. Comcast plays so many games to upsell features you will never use though their crappy gateway to get a discount.

JKnott

@ronv42

I'm on Rogers and they use the same equipment as Comcast. However, there is a setting in pfSense that may affect this. It's System / Advanced / Networking / Do not allow PD/Address release. If that's not selected, the prefix will change frequently.

Patch

@JKnott said in SLAAC versus DHCPv6:

line about dynamic is better for privacy is wrong. With SLAAC you get up to 7 privacy addresses, based on a random number.

they are all in the same range provided by the ISP, readily revealed by masking the address of any one of these addresses.

A dynamic ISP address range publishes which ISP the user is connected to the internet by
A static ISP address publishes your personal address range

Then if one of the devices on your network has location services enabled for "Network & Wireless" or through your browser then the "privacy" addresses have your street address encoded in every internet communication.

Recording addresses over time is likely to reveal what the 7 "private" addresses are for each device.

So a static IP address range is not really very private at all in my opinion.

JKnott

@Patch said in SLAAC versus DHCPv6:

they are all in the same range provided by the ISP, readily revealed by masking the address of any one of these addresses.

A dynamic ISP address range publishes which ISP the user is connected to the internet by
A static ISP address publishes your personal address range
recording addresses over time is likely to reveal what the 7 "private" addresses are for each device

My WAN address is provided by DHCPv6, along with my prefix. It makes no difference whether I use SLAAC or DHCPv6 on my LAN, with regard to my prefix. It will be the same either way. The only issue is whether the ISP will honour the DUID.

One other thing, with the huge address block within a /64, an attacker would have a hard time finding something to attack, even if they knew the prefix. A single /64 contains 18.4 billion, billion addresses. Compare this to a bit over 4 billion for the entire IPv4 address range. Of course there's a firewall called pfSense that goes a long way to keeping attackers out!

ronv42

@JKnott said in SLAAC versus DHCPv6:

One other thing, with the huge address block within a /64, an attacker would have a hard time finding something to attack, even if they knew the prefix. A single /64 contains 18.4 billion, billion addresses. Compare this to a bit over 4 billion for the entire IPv4 address range. Of course, there's a firewall called pfSense that goes a long way to keeping attackers out!

Now do the math with a /60: 16 x 18.4 billion - There is a reason I never see IPv6 address scans, but I still see port scans once a nefarious site logs your IPv6 they have the basic IP subnet, and it would take forever to scan through all those addresses.

JKnott

@ronv42

With my /56, it's 256 /64s. Yeah, it would take a while. I mentioned privacy addresses. They have a lifetime of 7 days. After that, they'd have to start over to find another address.

Jung-Fernmelder

Here is the guy who started the conversation. Thank you very much for all the information and the discussion. This helps me.

Conclusion:
Use SLAAC for clients and DHCPv6 for servers.

@keyser said in SLAAC versus DHCPv6:

is a PITA to get IPv6 working properly

+1
IPv6 is much more complicated than IPv4. And that's okay. Everybody involved in networking should be able to learn the IPv6 basics.
But the ISPs have messed it up, espceially with frequent prefix renewals which are heavy to handle and unnecessary. Three or four IPv6 prefix renewals per year would be enough.

Patch

@JKnott said in SLAAC versus DHCPv6:

It makes no difference whether I use SLAAC or DHCPv6 on my LAN, with regard to my prefix

Correct

@JKnott said in SLAAC versus DHCPv6:

One other thing, with the huge address block within a /64, an attacker would have a hard time finding something to attack

That is not an address privacy issue, but it maybe part of a network servers exposure to the internet. Network protection by obfuscation is not really a good approach, as it fails repidly if someone takes the time to look especially if they can get a hint were to look from another source (human engineering, traffic monitoring etc). Direct protection using a decent firewall is far better.

@JKnott said in SLAAC versus DHCPv6:

With SLAAC you get up to 7 privacy addresses, based on a random number.

As I have tried to explain, 7 networks addresses is a tiny number and everyone of these addresses has the same prefix.

If your ISP is giving you a static prefix, the the prefix will almost certainly encode / reveal your street address every time you make an internet connection from any device on your local network. My interpretation of which is the "SLAAC Privacy addresses" you are using maybe making you feel you have achieved something but they actually provide almost no privacy functionality.
If your ISP is giving you a dynamic prefix, the prefix will encode / reveal what ISP you are using but not which service or your street address. If you then add some randomisation of the lower order bits for each device you may achieved some privacy (not as much as a VPN or routing randomisation Tor tries to achieve).

@Jung-Fernmelder said in SLAAC versus DHCPv6:

ISPs have messed it up, espceially with frequent prefix renewals which are heavy to handle and unnecessary.

They are offering some internet privacy to those user who like some privacy. If you don't value privacy then perusing the options for a static IP address would be appropriate for you.