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

Bob Hinden <> Wed, 14 October 2020 21:46 UTC

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From: Bob Hinden <>
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Date: Wed, 14 Oct 2020 14:46:44 -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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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.


> 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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