Use of both dhcp and slaac, advanced configuration

crc_error_79 · May 28, 2023, 10:56 AM

@Bob-Dig
I can't use track interface because my isp assigns to the wan a local link.. Also I don't want to use nat..

I think that this way or the one @JKnott suggested are the better, but maybe I am wrong (am an home user not an network engineer )

My goal is to have a single point where to control all the devices connected to the lan so I can set to each device a name and network information.
I can do it with dhcp (+dns) but not with slaac (or at least I think, I need some examples or try it)

Bob.Dig · May 28, 2023, 11:01 AM

@crc_error_79 said in Use of both dhcp and slaac, advanced configuration:

I can't use track interface because my isp assigns to the wan a local link..

Does this defeat track interface?

crc_error_79 · May 28, 2023, 11:06 AM

@Bob-Dig
I don't know, as said am not an expert..

but if I set track interface on the lan the only option is WAN and it has a local link, not routable.. see? I am using pppoe for the ipv4 connection

Bob.Dig · May 28, 2023, 11:21 AM

@crc_error_79 said in Use of both dhcp and slaac, advanced configuration:

but if I set track interface on the lan the only option is WAN and it has a local link, not routable.. see? I am using pppoe for the ipv4 connection

Just try it, ping an IPv6 address from an interface which "tracks". Do a reboot to be sure.

crc_error_79 · May 28, 2023, 11:22 AM

@Bob-Dig
Ok but I need a IPv6 Prefix ID, I never use track interface, where I can get it?

Bob.Dig · May 28, 2023, 11:30 AM

@crc_error_79 Just use 0 on your first LAN. But on WAN you have to put in the delegation size to you. If you are uncertain, use 60.

crc_error_79 · May 28, 2023, 12:11 PM

@Bob-Dig
I tried but it is not work because (I think) the slaac can't autoassign an ipv6 if the gateway is a local link

JKnott · May 28, 2023, 1:53 PM

@crc_error_79

You seem to be creating your own problems. Use SLAAC to get the prefix for each interface for global addresses. Use my instructions for ULA and forget about DHCPv6, you don't need it.

JKnott · May 28, 2023, 12:43 PM

@crc_error_79 said in Use of both dhcp and slaac, advanced configuration:

but if I set track interface on the lan the only option is WAN and it has a local link, not routable.. see? I am using pppoe for the ipv4 connection

Use SLAAC. Why are you worrying about the link local address? That's entirely normal. With IPv6, the link local address is frequently used for routing. That link local address is used only for reaching the next hop and has nothing to do with whatever addresses you are assigned.

JKnott · May 28, 2023, 12:45 PM

@crc_error_79 said in Use of both dhcp and slaac, advanced configuration:

Ok but I need a IPv6 Prefix ID, I never use track interface, where I can get it?

With DHCPv6-PD, your prefix is assigned to you.

JKnott · May 28, 2023, 12:45 PM

@Bob-Dig said in Use of both dhcp and slaac, advanced configuration:

Just use 0 on your first LAN. But on WAN you have to put in the delegation size to you. If you are uncertain, use 60.

I believe he said he gets a /56, so that's what he would use.

JKnott · May 28, 2023, 12:46 PM

@crc_error_79 said in Use of both dhcp and slaac, advanced configuration:

I tried but it is not work because (I think) the slaac can't autoassign an ipv6 if the gateway is a local link

Where are you getting this nonsense from?

crc_error_79 · May 28, 2023, 1:55 PM

@JKnott said in Use of both dhcp and slaac, advanced configuration:

@crc_error_79

You seem to be creating your own problems. Use SLAAC to get the prefix for each interface for global addresses. Use my instructions for ULA and forget about DHCPv6, you don't need it.

On my post 16 my problems were solved, that was exactly my goal, then I asked if there were a better or more security / efficient etc way to do it.

I used your guide and it worked to, but in that way (with my skills) I can't easy manage the devices connected to the network since with slaac all devices get only the prefix and not the entire address.
So on router side if I don't know which ip has a device how can I manage it (firewall rules etc)

I think that with slaac I can't do a thing like this below. I have to use dns with the hope that the address doesn't change.

Also if the prefix changes (for any reason) how can I be sure that the remaining part will stay the same?

@JKnott said in Use of both dhcp and slaac, advanced configuration:

With DHCPv6-PD, your prefix is assigned to you.

To configure the wan, I followed this guide from my isp link, ok it is in Italian but you can look at the pictures, they said to use "static ipv6", add the given /56 + the remain part to create the network and the gateway, and that is what I initially did.

@JKnott said in Use of both dhcp and slaac, advanced configuration:

I believe he said he gets a /56, so that's what he would use.

yes I get a /56

@JKnott said in Use of both dhcp and slaac, advanced configuration:

Where are you getting this nonsense from?

If I set "track interface" -> WAN instead of "static" but that interface has a local link it don't work, at least to me.

[edit] correct the post link (16, not 15)

Bob.Dig · May 28, 2023, 2:49 PM

@crc_error_79 It looks like you get a static prefix, that is great, so forget "track interface".

Also you can use the DHCPv6 Server for static mappings, it is almost the same as with IPv4.

If you really think that you will switch ISPs in the near future, use NPt. It is not regular NAT and will work just fine with ULAs, as long as you have (only) one ISP.

crc_error_79 · May 28, 2023, 2:59 PM

@Bob-Dig
Thanks I will read something about (because the only thing I know about is that it is a sort of nat)

Bob.Dig · May 28, 2023, 3:49 PM

@crc_error_79 said in Use of both dhcp and slaac, advanced configuration:

(because the only thing I know about is that it is a sort of nat)

It doesn't has the problem of being only one address everything has to be NATed to but maybe don't start your IPv6 journey with that.

JKnott · May 28, 2023, 5:22 PM

@crc_error_79 said in Use of both dhcp and slaac, advanced configuration:

I used your guide and it worked to, but in that way (with my skills) I can't easy manage the devices connected to the network since with slaac all devices get only the prefix and not the entire address.

What is it you're trying to manage? When you use the consistent address for DNS, you will always be able to reach it, no matter what the privacy addresses are.

crc_error_79 · May 28, 2023, 5:28 PM

@JKnott
you are right but how can I set an host override on the dns resolver if I don't know the ipv6 address?
I must go around the house and check every devices.. If I use dhcpv6 all is "centralized" since the router knows every ip it leases
Or am I wrong?

JKnott · May 28, 2023, 5:33 PM

@crc_error_79

You don't set a host override. You just use the address as is. I mentioned I had to determine the consistent address recently for a new tablet. The way I did that was set up Packet Capture to capture the tablet MAC address and only IPv6. Then whatever address turned up when I used a browser to access the Internet was not the persistent address. Since there was only 2 address displayed in the settings, I had a good idea which one was persistent. You can easily grab the MAC address when you convert an IPv4 DHCP address, found in the DHCP log, to host override.

JKnott · May 28, 2023, 5:41 PM

@crc_error_79

Here's another way to determine the persistent address. This is on Linux, using the ip -6 address show command.

inet6 fd48:1a37:2160:0:90b4:60da:a900:2997/64 scope global temporary dynamic
inet6 fd48:1a37:2160:0:d37b:1ca2:4d85:a38d/64 scope global temporary deprecated dynamic
inet6 fd48:1a37:2160:0:76d4:35ff:fe5b:f5fa/64 scope global dynamic mngtmpaddr

I used grep to display only my ULA addresses. You can tell by reading the text which is the persistent address. It's the last one. Similar can be done with the ifconfig command on Linux and FreeBSD or ipconfig on Windows.