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

Bob Hinden <bob.hinden@gmail.com> Wed, 14 October 2020 23:42 UTC

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From: Bob Hinden <bob.hinden@gmail.com>
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Date: Wed, 14 Oct 2020 16:42:34 -0700
In-Reply-To: <e96bd8b4ad4b42259f71ad3314fe9066@boeing.com>
Cc: Bob Hinden <bob.hinden@gmail.com>, Philip Homburg <pch-v6ops-9@u-1.phicoh.com>, "v6ops@ietf.org" <v6ops@ietf.org>, dhcwg <dhcwg@ietf.org>, IPv6 List <ipv6@ietf.org>
To: "Templin (US), Fred L" <Fred.L.Templin@boeing.com>
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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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Fred,

> On Oct 14, 2020, at 8:55 AM, Templin (US), Fred L <Fred.L.Templin@boeing.com> wrote:
> 
> Philip,
> 
>> 2) Multiple downstream routers on a single link where the downstream routers
>>   also do not speak a routing protocol. I doubt that we need to support
>>   this configuration.
> 
> That depends on how you define "routing protocol". DHCPv6 PD driven
> by IPv6 ND router discovery would in spirit constitute a routing protocol.

DHCPv6 PD / IPv6 ND is not a routing protocol.  Routing protocols are things like OSPF, BGP, Babel, ISIS, etc.

Bob

> 
> Thanks - Fred
> 
>> -----Original Message-----
>> From: dhcwg [mailto:dhcwg-bounces@ietf.org] On Behalf Of Philip Homburg
>> Sent: Wednesday, October 14, 2020 5:16 AM
>> To: v6ops@ietf.org
>> Cc: dhcwg <dhcwg@ietf.org>rg>; 6man <ipv6@ietf.org>
>> Subject: [EXTERNAL] Re: [dhcwg] [v6ops] Re: Question to DHCPv6 Relay Implementors regarding draft-ietf-dhc-dhcpv6-pd-relay-
>> requirements
>> 
>> This message was sent from outside of Boeing. Please do not click links or open attachments unless you recognize the sender and
>> know that the content is safe.
>> 
>> 
>>> [if - Theres a couple of problems that this requirement is trying
>>> to address:
>>> 
>>> 1, A misbehaving client (accidentally or otherwise) 2, The volume
>>> of traffic being forwarded by the relay consumes the available
>>> bandwidth meaning that DHCP configuration cant complete
>>> 
>>> In both cases, the client cant be relied on to solve the problem]
>> 
>> I wonder if the problem can be stated in a more general way.
>> 
>> It seems to me that router should only forward a packet back to the link it
>> came from when it got the packet directly from a host.
>> 
>> I.e., a host may send a packet to a default router when the best next hop
>> happens to be different router on the same link. A host may also send a
>> packet to a default router when the host doesn't know that the destination
>> is on-link (on NBMA links for example).
>> 
>> In contrast, routers can be relied on to send packet to the correct next hop.
>> If they don't, then there is something inconsistent in the routing information.
>> Routers don't react to redirect ICMPs, so this inconsistency could waste a
>> lot of bandwidth.
>> 
>> One option is to only forward a packet back to the same link if we can also
>> send a redirect ICMP (ignoring rate limiting). I.e., Section 8.2 of RFC 4861
>> (Neighbor Discovery) describes that a redirect ICMP can be send if
>> "the Source Address field of the packet identifies a neighbor"
>> 
>> This could be implemented both in the downstream router and in the upstream
>> router.
>> 
>> I can see two cases where this could go wrong:
>> 1) multi-homed hosts doing something weird. In that case the host should be
>>   fixed.
>> 2) Multiple downstream routers on a single link where the downstream routers
>>   also do not speak a routing protocol. I doubt that we need to support
>>   this configuration.
>> 
>> _______________________________________________
>> dhcwg mailing list
>> dhcwg@ietf.org
>> https://www.ietf.org/mailman/listinfo/dhcwg
> 
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