Re: [mpls] [Gen-art] review: draft-ietf-mpls-lsp-ping-relay-reply-04

["Joel M. Halpern" <[e-mail]>]

ou are saying that this is only for the case where an AS is using public
addresses for its internal numbering, but is not distributing that
address block externally?

If so, you need to state that very clearly.
I believe a far more common case is one where the numbering is from a
portion of a publicly allocated space, but firewalled.  Which would
produce the same problem, but would not be amenable to this solution.
And it is well known that many ISPs do internal number assignment from
private blocks.

So what you are now saying is that this draft solves a very small
portion of the problem?  But it works for that small portion?  If so, at
the very least you need to be VERY clear about what cases this works for
and what cases it does not.  And I fear that even if you are clear, it
is going to be very confusing for folks who are trying to use it.

Yours,
Joel

On 10/21/14, 10:51 PM, Lizhong Jin wrote:
> Hi Joel,
> I now see your concern. The "private" word in draft is not correct, I will
> remove it. The original motivation of "draft-relay-reply" is from the
> scenario where IP address distribution is restricted among AS or IGP area.
> And the IP address is not private address. As I know, most deployed inter-AS
> or inter-area MPLS LSP is in the network without private IP address.
> 
> Regards
> Lizhong
> 
> 
>> -----Original Message-----
>> From: Joel M. Halpern [mailto:[e-mail]]
>> Sent: 2014年10月22日 10:15
>> To: Lizhong Jin
>> Cc: [e-mail]; [e-mail]; [e-mail];
> 'draft-ietf-mpls-lsp-ping-
>> relay-reply.all'
>> Subject: Re: [mpls] [Gen-art] review:
> draft-ietf-mpls-lsp-ping-relay-reply-04
>>
>> The problem is that the original source A, that we are trying to reach
> with a
>> reply, has an address that appears to the responder X to be routable.  But
>> the destination that is reached by that address is either a black hole or
> some
>> other entity using the same address.
>>
>> The reason for the duplication is that, as described in the draft, the
> source
>> address for A is a private address.  That same address may well be
> reachable
>> according to the routing table at X.  But it won't get to A.
>>
>> If the problem is something other than private addressing preventing
>> reachability, it is likely there is still a mistaken routability problem,
> but I can
>> not illustrate the failure without some other case being described.
>>
>> Yours,
>> Joel
>>
>> On 10/21/14, 10:06 PM, Lizhong Jin wrote:
>>> Inline, thanks.
>>>
>>>> -----Original Message-----
>>>> From: Joel M. Halpern [mailto:[e-mail]]
>>>> Sent: 2014年10月22日 0:06
>>>> To: [e-mail]
>>>> Cc: [e-mail]; [e-mail]; [e-mail];
>>> draft-ietf-mpls-lsp-ping-
>>>> relay-reply.all
>>>> Subject: Re: [mpls] [Gen-art] review:
>>> draft-ietf-mpls-lsp-ping-relay-reply-04
>>>>
>>>> In line.
>>>>
>>>> On 10/21/14, 10:36 AM, [e-mail] wrote:
>>>>> Hi Joel, see inline below, thanks.
>>>>>
>>>>> Lizhong
>>>>>
>>>>>
>>>>>> 2014.10.21，PM9:30，Joel M. Halpern <[e-mail]> wrote ：
>>>>>>
>>>>>> If the process for this draft is to use the top address that can be
>>>>>> reached in the routing table, then there is a significant
>>>>>> probability that the original source address, which is always at
>>>>>> the top of the list, will be used.  As such, the intended problem
>>>>>> will not be solved.
>>>>> [Lizhong] let me give an example to explain: the source address A is
>>>>> firstly added to the stack, then a second routable address B for
>>>>> replying AS is also added. The reply node will not use address A
>>>>> since it's not routable, then it will use address B. So it will work
>>>>> and I don't see the problem.
>>>>
>>>> The whole point of this relay mechanism, as I understand it, is to
>>>> cope
>>> with
>>>> the case when the responder X can not actually reach the source A.
>>>>    Now suppose that the packet arrives at X with the Address stack A, B,
> ...
>>> X
>>>> examines the stack.  The domain of A was numbered using net 10.
>>>> The domain of X is numbered using net 10.  A's address is probably
>>> routable
>>>> in X's routing table.  The problem is, that routing will not get to
>>>> A.  X
>>> examines
>>>> the stack, determines that A is "routable", and sends the packet.
>>>> This
>>> fails to
>>>> meet the goal.
>>> [Lizhong] The source A you are referring is the initiator, right? The
>>> goal of relay mechanism is to reach the initiator. If X is routable to
>>> the initiator (address A), then it is great, other relay node in the
>>> stack will be skipped.
>>> If the source A you are referring is the interface address of one
>>> intermediate node, then I do not understand "routing will not get to
>>> A.  X examines the stack, determines that A is "routable", and sends the
>> packet".
>>> Why routing will not get to A, but A is routable?
>>>
>>> Regards
>>> Lizhong
>>>
>>>
>>>>
>>>> Yours,
>>>> Joel
>>>
>>>
>>>
>