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Re: CPE router acting as host on its WAN interface (RE: draft-ietf-v6ops-ipv6-cpe-router-03.txt WGLC)
Fred,
the IsRouter flag only has value to a host, so that it can detect that
its default router is changing state from a router to a host. in this
scenario which is really a router-to-router link I cannot see any
problem with the service provider end getting the flag wrong. it is
after all not used for anything on a routed interface.
if an implementation deletes neighbor entries on a routed interface
based on a change in this flag, then that's a bug.
cheers,
Ole
On Tue, Jan 5, 2010 at 2:00 AM, Templin, Fred L
<Fred.L.Templin@boeing.com> wrote:
> Fred,
>
> A concern I raised on the list a while back centers around
> the behavior of the CPE router acting as a host on its WAN
> interface per section 4.1:
>
> "When the router is attached to the WAN interface link it must act as
> an IPv6 host for the purposes of stateless or stateful interface
> address assignment ([RFC4862]/[RFC3315])."
>
> and per WPD-3:
>
> "WPD-3: Absent of other routing information the IPv6 CE router MUST
> use Router Discovery as specified in [RFC4861] to discover a
> default router and install a default route in its routing
> table with the discovered router's address as the next-hop."
>
> To my understanding, this behavior would involve the CPE
> router sending Router Solicitation (RS) messages on its
> WAN interface in order to receive Router Advertisement (RA)
> messages. According to Section 6.2.6 of RFC4861, however:
>
> "Whether or not a Source Link-Layer
> Address option is provided, if a Neighbor Cache entry for the
> (RS)'s sender exists (or is created) the entry's IsRouter flag
> MUST be set to FALSE."
>
> RFC4861 goes to some level of detail to specify the setting
> of the IsRouter flag under various circumstances (including
> the RS case), but it only says what actions should be taken
> based on the flag as result of receiving Neighbor Advertisement
> messages. Other actions based on the IsRouter flag setting do
> not seem to be specified.
>
> In the linux kernel, it appears that the kernel will in some
> circumstances garbage-collect FIB entries that have a nexthop
> with the IsRouter flag set to FALSE. It is not clear what other
> router implementations would do based on the IsRouter setting,
> but it seems odd that the IsRouter flag in neighbor cache
> entries corresponding to CPE routers would be set to FALSE
> which in the linux case at least may lead to interoperability
> issues.
>
> As a result, it might be worth reconsidering whether it is
> appropriate for the CPE router to send an RS which might
> confuse other routers into thinking it is a host.
>
> Fred
> fred.l.templin@boeing.com
>
>> -----Original Message-----
>> From: owner-v6ops@ops.ietf.org [mailto:owner-v6ops@ops.ietf.org] On Behalf Of Fred Baker
>> Sent: Monday, January 04, 2010 7:45 AM
>> To: v6ops@ops.ietf.org
>> Cc: kurtis@kurtis.pp.se; rbonica@juniper.net
>> Subject: draft-ietf-v6ops-ipv6-cpe-router-03.txt WGLC
>>
>> This is to initiate a two week working group last call of draft-ietf-
>> v6ops-ipv6-cpe-router-03.txt. Please read it now. If you find nits
>> (spelling errors, minor suggested wording changes, etc), comment to
>> the authors; if you find greater issues, such as disagreeing with a
>> statement or finding additional issues that need to be addressed,
>> please post your comments to the list.
>>
>> We are looking specifically for comments on the importance of the
>> document as well as its content. If you have read the document and
>> believe it to be of operational utility, that is also an important
>> comment to make.
>>
>>
>>
>>
>> On Dec 18, 2009, at 2:45 AM, internet-drafts@ietf.org wrote:
>>
>> A New Internet-Draft is available from the on-line Internet-Drafts
>> directories.
>> This draft is a work item of the IPv6 Operations Working Group of the
>> IETF.
>>
>>
>> Title : Basic Requirements for IPv6 Customer Edge Routers
>> Author(s) : H. Singh, et al.
>> Filename : draft-ietf-v6ops-ipv6-cpe-router-03.txt
>> Pages : 14
>> Date : 2009-12-18
>>
>> This document specifies requirements for an IPv6 Customer Edge (CE)
>> router. Specifically, the current version of this document focuses
>> on the provisioning of an IPv6 CE router and the provisioning of IPv6
>> hosts attached to it.
>>
>> Status of this Memo
>>
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>>
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