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

Bob Hinden <> Wed, 14 October 2020 22:27 UTC

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From: Bob Hinden <>
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Date: Wed, 14 Oct 2020 15:27:34 -0700
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Cc: Bob Hinden <>, Michael Richardson <>, dhcwg <>, IPv6 List <>, v6ops list <>
To: "Templin (US), Fred L" <>
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Subject: Re: [dhcwg] [EXTERNAL] [v6ops] Re: Question to DHCPv6 Relay Implementors regarding draft-ietf-dhc-dhcpv6-pd-relay-requirements
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I note that the lack of “challenge” does not mean anyone agrees.   Agreement needs to be affirmative.


> On Oct 14, 2020, at 3:24 PM, Templin (US), Fred L <> wrote:
> Bob, several messages back it was established that the issue at the heart of this
> discussion is not specific to DHCPv6 nor DHCPv6-PD. Instead, it is an issue that is
> common to any situation where there are multiple "stub" IPv6 routers on a
> downstream link from a "default" IPv6 router, no matter how the routing
> information is established or maintained. So far, no one has challenged my
> assertion that this is a generic (and not a DHCPv6-PD-specific) IPv6 issue and
> I have been waiting to see if anyone wants to challenge that.
> Fred
>> -----Original Message-----
>> From: Bob Hinden []
>> Sent: Wednesday, October 14, 2020 2:47 PM
>> To: Templin (US), Fred L <>
>> Cc: Bob Hinden <>om>; Michael Richardson <>ca>; dhcwg <>rg>; IPv6 List
>> <>rg>; v6ops list <>
>> Subject: Re: [EXTERNAL] [dhcwg] [v6ops] Re: Question to DHCPv6 Relay Implementors regarding draft-ietf-dhc-dhcpv6-pd-relay-
>> requirements
>> With my chair hat on, is there a reason why this discussion is being copied to the 6MAN w.g.?   6MAN doesn’t maintain DHCP related
>> items.
>> Please remove from this thread.
>> Bob
>>> On Oct 14, 2020, at 12:19 PM, Templin (US), Fred L <> wrote:
>>> Hi Michael,
>>>> -----Original Message-----
>>>> From: Michael Richardson []
>>>> Sent: Wednesday, October 14, 2020 11:58 AM
>>>> To: Templin (US), Fred L <>
>>>> Cc:; Jen Linkova <>om>; dhcwg <>rg>; v6ops list <>rg>; 6man
>>>> <>
>>>> Subject: Re: [EXTERNAL] Re: [dhcwg] [v6ops] Re: Question to DHCPv6 Relay Implementors regarding draft-ietf-dhc-dhcpv6-pd-
>> relay-
>>>> requirements
>>>> Templin (US), Fred L <> wrote:
>>>>> Michael, what I was referring to below as "failure" is the proxy case when
>>>>> there is an L2 proxy P between the client and relay (e.g.,
>>>>> RFC489). There
>>>> RFC4389 describes an ND Proxy.
>>>> Is that really an L2 proxy?
>>> Yes, I believe it is an L2 proxy.
>>>> It seems like it also must be contain either an L2-bridge, or must have the
>>>> L3-routing table entries if it would really be capable of passing DHCPv6-PD
>>>> prefixes through it.
>>> The only thing it has that includes L3 information is neighbor cache entries that
>>> keep track of the client's actual L2 address on the downstream link segment,
>>> but rewrites the client's L2 address to its own L2 address when forwarding
>>> onto an upstream link segment. (In the reverse direction, it receives packets
>>> destined to its own L2 address but the client's L3 address on the upstream
>>> link segment, then rewrites the L2 address to the client's L2 address when
>>> forwarding onto the downstream link segment.)
>>>> Can you explain how such a device would normally work for a client device
>>>> A,B,C,D doing DHCPv6-PD through it?
>>> Sure. A sends a DHCPv6 Solicit using its IPv6 link-local address as the source,
>>> and its L2 address as the link-layer source. The proxy converts the link-layer
>>> source to its own L2 address when forwarding the DHCPv6 solicit onto the
>>> upstream link. When the DHCPv6 Reply comes back, the IPv6 destination is
>>> that of client A, but the link-layer destination is the L2 address of the proxy.
>>> The proxy then converts the L2 destination to the address of client A and
>>> forwards it on to the client.
>>>> And is the failure one where the router "R" fails to drop traffic it should,
>>>> one where the router "R" drops traffic that it shouldn't?
>>> I was thinking more along the lines of the latter; if the only way that A has
>>> for talking to B, C, D, etc. is by going through R, it wouldn't work if R was
>>> unconditionally dropping everything.
>>> Thanks - Fred
>>>> --
>>>> Michael Richardson <>   . o O ( IPv6 IøT consulting )
>>>>          Sandelman Software Works Inc, Ottawa and Worldwide
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