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

"Templin (US), Fred L" <> Wed, 07 October 2020 13:51 UTC

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From: "Templin (US), Fred L" <>
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Thread-Topic: [EXTERNAL] [dhcwg] Question to DHCPv6 Relay Implementors regarding draft-ietf-dhc-dhcpv6-pd-relay-requirements
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Subject: Re: [dhcwg] [EXTERNAL] Question to DHCPv6 Relay Implementors regarding draft-ietf-dhc-dhcpv6-pd-relay-requirements
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We implement DHCPv6 PD on relays. The relay is always co-resident with the
delegating server and behaves according to RFC6221. Are we covered?

Thanks - Fred

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

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We are currently finishing WGLC for this draft. It describes requirements for a 'DHCPv6 Delegating Relay' - this is a router functioning as the L3 edge and DHCPv6 relay (only) with prefix delegation. This is a common deployment scenario, but RFC3633/8415 only really describes PD using a Delegating Router - i.e the L3 edge also functions as a DHCPv6 server with no relay. When the relay and server functions are performed by separate devices a number of problems with how relays behave have
been observed, so this document addresses them.

During WGLC for this, Ole raised a comment related to one of the routing requirements:

R-4:    If the relay has learned a route for a delegated prefix via a
           given interface, and receives traffic on this interface with
           a destination address within the delegated prefix (that is
           not an on-link prefix for the relay), then it MUST be
           dropped.  This is to prevent routing loops.  An ICMPv6 Type
           1, Code 6 (Destination Unreachable, reject route to
           destination) error message MAY be sent back to the client.
           The ICMP policy SHOULD be configurable.

The problem that this is trying to solve is:

3.5.  Forwarding Loops between Client and Relay

   If the client loses information about a prefix that it is delegated
   while the lease entry and associated route is still active in the
   delegating relay, then the relay will forward traffic to the client
   which the client will return to the relay (which is the client's
   default gateway (learnt via an RA).  The loop will continue until
   either the client is successfully reprovisioned via DHCP, or the lease
   ages out in the relay.

Ole’s comment: "And I would also be happy if we could have some implementors chime in with a "we are happy and able to implement this requirement”.”

We would appreciate any feedback on this, especially from anyone with experience implementing DHCPv6 relays with PD.


Current draft version: