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Multiple IPv6 Prefix Delegation over AT&T Residential Gateway for pfSense
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dhcp6 ipv6 ipv6-prefix-delegation opnsense pfsense

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Multiple IPv6 Prefix Delegation over AT&T Residential Gateway for pfSense/opnSense

Known Compatible Versions

Known Kea DHCP Issues

As of pfSense 23.09, Kea DHCP is being pushed as the suggested default for DHCP needs. Kea DHCP works out-of-the-box with this guide. There is some instability with Kea around IPv6 that may prevent the kea-dhcp6 service from starting. For example, the following error message may appear:

DHCP6_INIT_FAIL failed to initialize Kea server: configuration error using file '/usr/local/etc/kea/kea-dhcp6.conf': cannot lock socket lockfile, /tmp/kea6-ctrl-socket.lock, : Resource temporarily unavailable

This can be corrected by deleting the offending /tmp/kea6-ctrl-socket.lock file and restarting the service via Services -> DHCPv6 Server.

Known working residential gateways (RGs)

Known Caveats

All credit goes to the user ttmcmurry from the Netgate Forum for his insight within the thread for which all of this was discussed.

I've been working on this one for a while. This is the result of others posting their work across various forums, reading BSD docs, and plenty of testing as a result of needing something to do while being stuck at home. :)

The purpose of this is to make it easier for AT&T customers who wish to assign more than one IPv6 prefix delegation inside their pfSense firewall to more than one internal network interface. I am providing an example dhcp.conf script and explaining what's needed step-by-step. AT&T customers must have been furnished a Residential Gateway (Pace 5268AC / Arris BGW210-700, possibly others) and have configured the RG in DMZ+/IP Passthrough mode. This has been written with pfSense 2.4.5 in mind.

Why do this? In short, AT&T U-Verse & Fiber customer equipment is assigned a /60 and can only hand out eight /64 prefix delegations. It is not possible to request a larger PD, however it is possible to request multiple /64 PDs from pfSense's WAN interface. Since the pfSense UI does not expose this functionality directly, it is possible to take advantage of it by supplying a dhcp.conf to override pfSense DHCP6 behavior available from the UI.

. . .

Once this script is in place, if you need to reassign interfaces & prefix delegations, the script has to be updated You will need to edit the IPv6 Track Interface Prefix ID on the LAN/OPT interfaces with the IA-PD you specify in the .conf file.

-ttmcmurry


pfSense/OPNsense Configuration Steps

Note: It is assumed that the WAN interface is named "WAN" throughout this guide. If it has a different name in your setup, that is ok. Substitute your WAN interface name where applicable throughout this guide.

0. Validate Initial Conditions

  1. The WAN interface IPv6 Configuration type is configured for "none"
  2. The WAN interface IPv6 DHCP6 Client Option "Do not allow PD/Address release" is UNCHECKED
    • This checkbox may not be present on some installs
  3. The LAN/OPT interfaces' DHCP6 option is set to "none"
  4. DHCPv6 Server & RA -> DHCP6 Server -> Disabled
  5. Services -> Router Advertisement -> Defaults

Note: Prior to pfSense 23.09, Router Advertisement was found under DHCPv6 Server & RA -> Router Advertisements

1. Create a local copy of the following config template

interface {YOUR_WAN_INTERFACE} {
    send ia-na 0;
    send ia-pd 0;
    send ia-pd 1;
    send ia-pd 2;
    send ia-pd 3;
    send ia-pd 4;
    send ia-pd 5;
        send ia-pd 6;
    send ia-pd 7;
    request domain-name-servers;
    request domain-name;
    script "/var/etc/dhcp6c_wan_script.sh";
};
id-assoc na 0 { };
id-assoc pd 0 {
    prefix-interface {YOUR_LAN_INTERFACE} {
        sla-id 0;
        sla-len 0;
    };
};
id-assoc pd 1 { 
    prefix-interface {YOUR_OTHER_LAN_INTERFACE} {
        sla-id 0;
        sla-len 0;
    };
};
id-assoc pd 2 { };
id-assoc pd 3 { };
id-assoc pd 4 { };
id-assoc pd 5 { };
id-assoc pd 6 { };
id-assoc pd 7 { };

Note: The script declaration in the above configuration may have a different path depending on the setup. For example, some systems may have the script located at /var/etc/dhcp6c_opt4_script.sh. Ensure that the correct file is referenced either via SSH or through Diagnostics -> Edit File.

2. Update the "interface" block on line 1

In the config template from step #1, replace {YOUR_WAN_INTERFACE} with the network port name for the WAN interface.

The network port name can be found under Interfaces -> Assignments.

Example:

Screenshot 2023-04-30 at 3 54 24 AM Screenshot 2023-04-30 at 3 57 09 AM

This results in the following configuration segment:

interface igc3 {
    send ia-na 0;
    send ia-pd 0;
    . . .

IA-NA Note: The IA-NA is an arbitrary number. A unique number must be chosen for each device connected to the AT&T residential gateway (RG) which will request a prefix delegation from the RG. If only one device will be requesting PDs from the RG (i.e. this pfSense firewall), then "ia-na 0" is fine.

3. Update the "ia-pd" declarations

In the config template from step #1, replace {YOUR_LAN_INTERFACE} with the network port name for the desired LAN interface.

Example:

Screenshot 2023-04-30 at 3 59 32 AM Screenshot 2023-04-30 at 4 00 36 AM

This results in the following configuration segment:

id-assoc pd 0 {
    prefix-interface igc0 {
        sla-id 0;
        sla-len 0;
    };
};
id-assoc pd 1 { 
    . . .

Network ports can be arbitrarily assigned to PDs, staring with pd 0 and working down the list. Note that formatting is specific. Each new PD declaration needs to be formatted exactly as id-assoc pd 0 is in the above example; only with an updated network port name.

The sla-id and sla-len declarations are always zero (0).

Note: If a particular PD is not desired, it does not need to be declared in the config file. The send ia-pd and its respective id-assoc pd declaration only needs to be declared if it is going to be used by an interface.

Note: Assigned PDs will result in numerically different networks, depending on the RG.

  • Pace 5268AC first assigns F then decrements to 8 to PD 0-7, i.e. PD0 = ::xxxF::/64
  • Arris BGW210-700 first assigns 8 then increments to F to PD 0-7, i.e. PD0 = ::xxx8::/64

4. Add the script to pfSense

5. Edit the WAN interface

  1. Navigate to Interfaces -> WAN
  2. Set the IPv6 Configuration Type to DHCP6
  3. Under the DHCP6 Client Configuration section, check the Advanced Configuration box
    • Ensure that the Configuration Override checkbox is unchecked during this portion, as having that box checked will hide UI elements that need to be accessed.
  4. Ensure all other check boxes in this section are unchecked.
  5. Set the DHCPv6 Prefix Delegation size to 60
  6. Re-check the Advanced Configuration checkbox
  7. Enter the path of the configuration override file from earlier into the Configuration File Override text box.
    • i.e., /usr/local/etc/rc.d/att-rg-dhcpv6-pd.conf
  8. Click the Save button and apply the changes

6. Edit the LAN/OPT interface(s), one at a time

  1. Under General Configuration, set the IPv6 Configuration Type to Track Interface
  2. Under Track IPv6 Interface, set the IPv6 Interface to the WAN interface name
  3. Set the IPv6 Prefix ID to the correlated PD number configured in the configuration file from earlier
  4. Click on the Save button and apply the changes

Example:

Screenshot 2023-04-30 at 3 59 32 AM Screenshot 2023-04-30 at 4 03 29 AM Screenshot 2023-04-30 at 4 06 49 AM

Note: Be sure to use the id-assoc pd number associated with the respective network port for the IPv6 Prefix ID.

7. Enable pfSense DHCPv6 Server

Navigate to Services -> DHCPv6 Server & RA

Perform the following actions for each interface:

Note: Prior to pfSense 23.09, Router Advertisement was found under DHCPv6 Server & RA -> Router Advertisements

Note: After applying these settings, it may take several minutes for IPv6 addresses to start populating approprately.

If all has gone well, IPv6 should now be working.

State Limits

AT&T Residential gateways have a state table that is far smaller than pfSense's defaults, which can result in problems once the RG begins tracking more states than available. pfSense should be set to never go above that limit. pfSense will adjust how states are managed based on its default adaptive algorithm from "Firewall Adaptive Timeouts." There is no need to adjust pfSense default Adaptive Timeout behavior, only the maximum number of states pfSesnse can use.

The values below are from known hardware & firmware capabilities. Depending on the # of devices directly plugged into the RG, like U-Verse set-top-boxes and devices NOT behind pfSense, you may need to adjust pfSense's maximum states downward. This information can be found on the RG under Settings -> Diagnostics -> NAT.

Set the pfSense state limit in Advanced -> Firewall & NAT -> Firewall Maximum States

Note: If anyone has more up-to-date information about RG firmware and state capabilities, let me know and I'll update this table.