Re: [pcp] A question: How can an internal client get the external IP and port of the inner NAT

On 25-Oct-2015 06:54 pm, Chenguohai <chenguohai@huawei.com> wrote: 
>  
>  
> Hi Dan,
>  
> Thank again.
> What is the workflow in nested NATs for internal host?
> 1: the client must judge how many NATs are there in the path and the order;

It doesn't need to perform (1) first.  In fact, it's impossible to determine how many NATs are on the path first.

> 2: nogotiate with the fisrt PCP server(in the most nested NAT) for the exteral IP and port;
> 3:use the negotiated IP and port with the second PCP server;
> 4 do step 2 and 3 until communicating to the most external PCP server.

Correct.  And after doing that, it will have determined how many PCP-supporting NATs are on the path.

>  
> Does this make sense?

Yes.

-d

>  
> BR
> G.Robert  Chen
> -------------------------------------------------------------------------------------------------------------------------------------
>  
> 发件人: 🔓Dan Wing [mailto:dwing@cisco.com] 
> 发送时间: 2015年10月24日 23:54
> 收件人: ChenGuohai
> 抄送: Chenguohai; pcp@ietf.org
> 主题: Re: [pcp] A question: How can an internal client get the external IP and port of the inner NAT
>  
> 
> On 23-Oct-2015 06:04 pm, ChenGuohai <chenguohai67@outlook.com <mailto:chenguohai67@outlook.com>> wrote:
> Hi Dan,
>  
> Many thanks for your explaination.
>  
> Inner NATs are mostly used in residents and external NATs are CGNs is the most common nested NAT case.
>  
> Using PCP means that the CPE(inner NAT) must embed a PCP server.  The PCP client should communicats with two PCP servers.
>  
> Right.
>  
> 
> 
> Using STUN means a STUN server need to be deployed between inner NAT and external NAT. Shall this be common?
>  
> Not that I have seen.
>  
> -d
>  
> 
> 
>  
> Manual configuration is very cost.
>  
>  
> BR
> G.Robert  Chen
>  
> Subject: Re: [pcp] A question: How can an internal client get the external IP and port of the inner NAT
> From: dwing@cisco.com <mailto:dwing@cisco.com>
> Date: Fri, 23 Oct 2015 10:44:15 -0700
> CC: pcp@ietf.org <mailto:pcp@ietf.org>; chenguohai67@outlook.com <mailto:chenguohai67@outlook.com>
> To: chenguohai@huawei.com <mailto:chenguohai@huawei.com>
> 
> On 22-Oct-2015 08:24 pm, Chenguohai <chenguohai@huawei.com <mailto:chenguohai@huawei.com>> wrote:
>  
>  
> Hi all,
> I am new to PCP and reading RFC6887.I have a question about section 8.1. On the upper part of page 22 writing following,
> the PCP-controlled NAT creating pointless non-functional mappings.
>    When such an intervening non-PCP-aware inner NAT is detected,
>    mappings must first be created by some other means in the inner NAT,
>    before mappings can be usefully created in the outer PCP-controlled
>    NAT.  Having created mappings in the inner NAT by some other means,
>    the PCP client should then use the inner NAT’s external address as
>    the client IP address, to signal to the outer PCP-controlled NAT that
>    the client is aware of the inner NAT, and has taken steps to create
>    mappings in it by some other means, so that mappings created in the
>    outer NAT will not be a pointless waste of resources.
>  
> My question is that how an interal client could get the external IP and port of the inner NAT.
>  
> PCP, UPnP IGD, STUN, manual configuration.
>  
> Should there be server between the inner NAT and the external one? How could it be assured that the inner NAT does not change external port?
>  
> Hopefully whatever mechanism the client used (PCP, UPnP IGD, STUN, manual configuration) would tell the client of such a change.
>  
> -d
>  
>  
>  
>  
> BR
> G.Robert  Chen
> -------------------------------------------------------------------------------------------------------------------------------------
> G.Robert  Chen (Chen Guohai  陈国海). Network Research Department, Huawei Technologies Co., Ltd. Telephone: 0086-25-56624606;   http://www.huawei.com <http://www.huawei.com/>
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