Question

From what I can tell, my mobile service provider allocates a /64 that is dynamic per session. Using the TRB500 as a gateway, I would like to delegate all of this to a downstream router for use but am stuck on a way to implement this (or if it's even possible).

Currently I have a TRB500 setup with the mob1s1a1 interface running in bridge mode. This works well for IPv4 with the ISP allocated CG-NAT address assigned directly to my downstream router. For attempting to create the same L3 transparency for IPv6 I have tried:

1. Setting RA, DHCPv6, and NDP all to relay on the bridged lan interface. When this happens the downstream router does not get a response to a DHCPv6 solicit.
2. Setting RA and DHCPv6 to server mode. In this config the downstream router does successfully negotiate an address for its interface but the DHCPv6 advertise packet includes an IA_PD with a NoPrefixAvail status. Looking at the OpenWRT docs, this is because there is not a suitable prefix size to support delegation.

There is a high chance there is something rather obvious I'm missing here. Any pointers as to what it is?

edit: environment details

• Device: TRB500
• Firmware: TRB5_R_00.07.04.3

Comments

Did you find an answer? I'm having the same struggle.

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Unfortunately not. I did find RFC 7278 and RFC 6653 which have some detail on the likely address assignment process from the mobile network side. Based on the info there I'm not overly confident this is possible.

There may be a way to achieve it via the flow defined in section 3.3 of 6653 but that requires support from both on the provider network and from the TRB500, neither of which I have the ability to implement.

I've also since found out that the mobile provider blocks incoming connections to the IPv6 addresses it hands out too. Since my original drive for setting this up was to work around CG-NAT I've not spent too much more time on it.

Answer 1

Hello,

  

Sorry for the delayed response.

We have done some testing with colleagues, but from the information we could find, this will not be possible. In order to pass /64 blocks of addresses to LAN clients, you need to have a bigger block (e.g. /56) assigned by your carrier. This seems to be a limitation of specification.

However, I'm in no way an expert in IPv6, so if anyone has any additional information on how this can be achieved, feel free to correct me.

Additionally, 3 IPv6 addresses are used up by the router itself - one is assigned to the mobile module, another to the WAN interface, and the last one as a LAN address.

  

Best regards,
DaumantasG