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

🔓Dan Wing <> Fri, 23 October 2015 17:44 UTC

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From: =?utf-8?Q?=F0=9F=94=93Dan_Wing?= <>
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Date: Fri, 23 Oct 2015 10:44:15 -0700
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To: Chenguohai <>
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Subject: Re: [pcp] A question: How can an internal client get the external IP and port of the inner NAT
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On 22-Oct-2015 08:24 pm, Chenguohai <> 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.


> BR
> G.Robert  Chen
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> G.Robert  Chen (Chen Guohai  陈国海). Network Research Department, Huawei Technologies Co., Ltd. Telephone: 0086-25-56624606; <>
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