Re: [dhcwg] [v6ops] [EXTERNAL] Re: Question to DHCPv6 Relay Implementors regarding draft-ietf-dhc-dhcpv6-pd-relay-requirements

Bjørn Mork <> Fri, 09 October 2020 07:37 UTC

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To: Ole Troan <>
Cc: "Templin \(US\)\, Fred L" <>, dhcwg <>, v6ops list <>, 6man <>, "Bernie Volz \(volz\)" <>
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Date: Fri, 09 Oct 2020 09:36:51 +0200
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Subject: Re: [dhcwg] [v6ops] [EXTERNAL] Re: Question to DHCPv6 Relay Implementors regarding draft-ietf-dhc-dhcpv6-pd-relay-requirements
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Ole Troan <> writes:
>> On 8 Oct 2020, at 23:55, Templin (US), Fred L <> wrote:
>> Now, client B sends packets destined to an address in A to R, and R forwards the
>> packets to client A since it still has a route for A. When the packets arrive at A,
>> however, A forwards them back to R since it has "forgotten" that it holds the
>> prefix A. When R receives the packets from A with destination address also
>> from prefix A, it must drop them instead of forwarding them back to A to
>> avoid looping.
> This is indeed what the requirement in the draft says. 
> This isn’t quite obvious how to implement, which why I brought up the
> question if anyone had implemented this. And if it’s supported in hw
> etc.

I don't know anything about hardware implementations or scaling in
general, but this seems easy to implement using the Linux kernel routing

 ip -6 rule add pref 1234 iif if_A to prefix_A blackhole

where 'if_A' is the interface connecting A to R and 'prefix_A' is the
prefix assigned to A.