Curious-Bob
Level 2: Rookie

DHCPv6 Prefix Delegation

What is the DHCPv6 Prefix Delegation (/64, /60 or /56 etc.) assigned to Mobile Broadband services?

 

 

CB

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11 REPLIES 11
cf4
Level 25: The Singularity
Level 25: The Singularity

Re: DHCPv6 Prefix Delegation

The IPv6 Prefix is equivalent to the subnet mask used for IPv4.

 

An IPv6 address is made up of 128 bits. A prefix indicates how many bits are used in the network part of the address.. A prefix of 64 indicates the the first 64 bits of the address allocated by the server are the network part and the remaining 64 bits can be used to assign the client its unique address.

 

 

       Network part                Client Part

               64            |                 64

xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx/64

 

  Network part         Client Part

      32      |                      96

xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx/32

Curious-Bob
Level 2: Rookie

Re: DHCPv6 Prefix Delegation

Thanks for your response cf4,

 

The minimum  IPv6 ‘Prefix Delegation’ that can be delegated to a network is /64, but a /64 cannot be routed.

 

I’m trying to use Telstra’s Mobile Broadband service with IPv6 for my home network, which involves a router with a couple of interfaces. Each interface requires a /64 (the minimum that can be delegated).

 

It is common (best practice) for an ISP to assign a /56 to each customer, which will allow routing at the customers equipment.

 

From what I can tell it appears that using the APN of ‘telstra.internet’ does not use a IPv6 ‘Prefix Delegation’, which is fine for a single device (tablet etc.) but not for a home broadband service. I’ve tried looking for configuration details but nothing seems to be published anywhere…

 

So now I have two questions:

- What is the correct APN to use for Telstra’s Mobile Broadband for a home network; one that provides an IPv6 Prefix Delegation (IPv6 PD)?

- What is the IPv6 Prefix Delegation that Telstra uses for its Mobile Broadband service?

CB
cf4
Level 25: The Singularity
Level 25: The Singularity

Re: DHCPv6 Prefix Delegation

To obtain an IPv6 address on the mobile service change the PDP type in the APN settings to IPv4/v6 or IPv4 from IPv4

 

From memory the same prefix is used on the mobile broadband network as used on the fixed broadband network.

Mkrtich
Level 21: Augmented
Level 21: Augmented

Re: DHCPv6 Prefix Delegation

Hi - the Telstra Gen 2 Arcadyan LH:1000 modem for NBN  uses the /56 Prefix Delegation for is IPv6 primary WAN - see Go to Advanced/Internet/Internet Access. The adjacent LTE folio shows the properties of the BackUp WAN and allows editing of certain fields e.g. set as dual stack. There is no Prefix delegation listed on this section - I think because it is being treated as a Mobile Broadband Data only Hotspot device limited for outgoing data connections only.

 

I don't think external incoming parties can connect to any data LAN device when the modem operates in 4G LTE Back Up WAN like in the primary WAN i.e. without knowing its real IPv6 address vs the alias IPv6 addresses. I haven't tested, so not sure if incoming Voice Calls work when the modem is in Back Up mode - if so, it would imply a special Telstra IPv6 arrangement for incoming Voice Calls where Telstra would control or have access to all the associated IPv6 information for the voice call.  

 

Do you have a 5G Home Broadband service using the Arcadyan 5G AW:1000 special modem for Fixed Home Broadband rather than a 5G Netgear or ZTE Mobile Hotspot - are you trying to access devices on your LAN from external sources or are you saying your data devices only operate in IPv6 mode? 

 

@cf4 's manual on the Arcadyan 5G modem may provide some clues (see CrowdSupport Wiki)  - currently, during the pre-release trial stage Port Forwarding is only operative when that Modem's Primary 5G WAN is OFF and the secondary wired WAN is used. That may or may not change in the future when the modem is available for general release. 

 

If you are a Business Customer, there may be different higher level functionality options that apply for your service. I am not familiar with these. 

Curious-Bob
Level 2: Rookie

Re: DHCPv6 Prefix Delegation

Thanks cf4 and Mkrtich,

 

Yes for NBN a /56 Prefix Delegation is normal and from what you’re seeing with your LTE settings leads me to believe that Telstra is not setting an IPv6 PD for it’s Mobile Broadband service.

 

I have a Netgear LB2120 (4G LTE Modem) in bridged mode connected to a Ubiquiti EdgeRouter 4.

 

The modem is configure to use the APN ’telstra.internet’ with IPv4/v6 and I can get both an IPv4 and IPv6 address to the WAN side of the router (the IPv4 side of things works without issue).

 

I’m not trying to allow incoming connections, just trying to get a working IPv6 address to the LAN interfaces and any devices connected to the LAN side of the router. This I believe requires Telstra to set a IPv6 PD…

CB
cf4
Level 25: The Singularity
Level 25: The Singularity

Re: DHCPv6 Prefix Delegation

On my Tablet I use telstra.wap as the APN name and have set the APN protocol to IPv4/IPv6. Checking Ipv6 at ipv6-test.com is successful on both the Tablet and a device connected to its hotspot.

 

Also checked using telstra.internet and Ipv6 test is successful. I think your problem is due to the Netgear LB2120 not passing on correct information to the Ubiquiti EdgeRouter 4 or wrong configuration in the Ubiquiti EdgeRouter 4

Curious-Bob
Level 2: Rookie

Re: DHCPv6 Prefix Delegation

Yes if I use the SIM in a tablet it works fine and if I connect a computer to the Netgear LB2120 I get both an IPv4 and IPv6 address, so I’m fairly sure that the Netgear modem is working correctly.

 

I’m trying to verify my EdgeRouter configuration and part of that is knowing the correct IPv6 PD, but I cannot find that information anywhere.

 

If anyone has a Mobile Broadband Modem (not using the NBN) and has devices connected to it that get an IPv6 address, please let me know…

CB
cf4
Level 25: The Singularity
Level 25: The Singularity

Re: DHCPv6 Prefix Delegation

Most mobile broadband ISPs don't provide a IPv6 PD but there is a work around. See link below.

 

https://tools.ietf.org/html/rfc7278

Mkrtich
Level 21: Augmented
Level 21: Augmented

Re: DHCPv6 Prefix Delegation

Hi - just to confirm, when the LB2120 is in Router mode, it is getting IPv4 and IPv6 addresses assigned to its connected devices. When the LB2120 is set to Bridge Mode, the Edge Router 4 does not show IPv6 addresses on its LAN connected devices.

 

If you haven't viewed it, this YouTube clip may assist you to discover what settings may need to be applied to your Ubiquiti Router - if the same screens apply to your model. It is dated 2019 with the Edge Router Lite version - in 2019, the set up processes for IPv6 using the Ubiquiti Set Up Wizard didn't activate the chosen IPv6 Prefix Definition input settings for its WAN - may have been fixed in late firmware.

 

The presenter uses the Config Screens to edit the detailed IPv6 settings in order to get IPv6 to a LAN device. He is directly connected to an RSP using PPPoE and not going through a 4G Modem, however the same principle may apply. A reply commentary underneath the video used DHCP and also referred to a whirlpool.net post - you might find some hints there as well. 

 

https://www.youtube.com/watch?v=AEt7LIxxKBU 

Curious-Bob
Level 2: Rookie

Re: DHCPv6 Prefix Delegation

Thanks cf4 and Mkrtich,

 

I think we have an answer to my original question, Telstra does not set a DHCPv6 Prefix Delegation (but if does it is a /64).

 

From the RFC-7278 I think I have a better understanding of what the LB2120 is doing with IPv6. 

I suspect it is using DHCPv6 on the Modem interface and assigning a /64 address to its LAN interface. This is not visible anywhere on the LB2120 web-interface…

 

I have the LB2120 configured to use the Telstra APN ‘telstra.internet’ with the PDP ‘IPV4V6’ and set it to ‘bridged mode’. 

 

Now when I connect a computer to the LB2120 LAN interface, I get both IPv4 and IPv6 addresses from Telstra.

 

Or with the EdgeRouter, I have set the WAN interface to use SLAAC (rather than DHCPv6) to get it’s IPv6 address and I have both IPv4 and IPv6 addresses from Telstra on the WAN interface.

 

CB
Mkrtich
Level 21: Augmented
Level 21: Augmented

Re: DHCPv6 Prefix Delegation

Thanks for your feedback. Hopefully it will help others readers in the future. 

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