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

Bjørn Mork <bjorn@mork.no> Fri, 09 October 2020 07:37 UTC

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From: =?utf-8?Q?Bj=C3=B8rn_Mork?= <bjorn@mork.no>
To: Ole Troan <otroan@employees.org>
Cc: "Templin \(US\)\, Fred L" <Fred.L.Templin@boeing.com>, dhcwg <dhcwg@ietf.org>, v6ops list <v6ops@ietf.org>, 6man <ipv6@ietf.org>, "Bernie Volz \(volz\)" <volz@cisco.com>
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References: <ff36a6d9f0834b5bbf331c6c40df16b8@boeing.com> <6373DDB1-753B-4E15-8097-9ED03F1BFC19@employees.org>
Date: Fri, 09 Oct 2020 09:36:51 +0200
In-Reply-To: <6373DDB1-753B-4E15-8097-9ED03F1BFC19@employees.org> (Ole Troan's message of "Thu, 8 Oct 2020 23:59:40 +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 <otroan@employees.org> writes:
>> On 8 Oct 2020, at 23:55, Templin (US), Fred L <Fred.L.Templin@boeing.com> 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
facilities:

 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.


Bjørn