Re: [BEHAVE] (no subject)

ivan c <ivan@cacaoweb.org> Tue, 18 June 2013 20:32 UTC

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To: "Senthil Sivakumar (ssenthil)" <ssenthil@cisco.com>
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Date: Tue, 18 Jun 2013 22:33:22 +0200
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Subject: Re: [BEHAVE] (no subject)
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Hi Senthil,

Thanks for your message. You might want to read
http://tools.ietf.org/html/draft-ietf-behave-requirements-update-00 
It features the list of updates to the existing RFC, adapted to new usage
contexts such as CGNs, mobile networks, etc.


On Tue, 18 Jun 2013 19:24:50 +0000, "Senthil Sivakumar (ssenthil)"

>>
>>Are you talking about UDP port preservation? 
> 
> Both TCP & UDP. The latest implementation in some router families is not
> to have port preservation
> (for both TCP & UDP).
> 

The discussion here is not about UDP. UDP port preservation should
generally not be implemented by NATs, as it could generate conflicts when 2
internal hosts using the same local port, each with a session to the same
endpoint. This would break end-to-end connectivity in rare cases, as there
is no fallback mechanism (as opposed to TCP).

To be clear, the requirements are as follows:
* NAT SHOULD NOT use UDP port preservation
* NAT SHOULD use TCP port preservation

Here are some NATs that have been tested and implement TCP port
preservation:
in the UK:
BT (British Telecom) (house-made gateway) - number 1 provider
Virgin (house-made gateway) - number 2 provider
Sky (Sagemcom) - number 3 provider

in France:
Orange (Livebox) (house-made gateway) - number 1 provider
Free (Freebox) (house-made gateway) - number 2 provider
SFR/Neuf (Neufbox) (house-made gateway) - number 3 provider

This covers the overwhelming majority of subscribers.

We have the same results in Spain in Italy.

Misc:
Linksys E1200, latest generation.
Netgear, various models


It is difficult to find any NAT that does *not* implement TCP port
preservation in these countries.
If you think some gateway implementations have dropped TCP port
preservation, you need to substantially support your claim by a reference.
We are not aware of anything that would support it. 


> 
> Most of the NATs that I know don’t do port overloading any more.
> RFC 5382 also says,
> REQ-7:  A NAT MUST NOT have a "Port assignment" behavior of "Port
>       overloading" for TCP.
> 

This is the purpose of the new draft
http://tools.ietf.org/html/draft-ietf-behave-requirements-update-00 , to
make the use case for port overloading, as it is needed in CGNs. It wasn't
needed nearly as much in 2005 when RFC 5382 was first written.

REQ-7: A NAT MUST NOT have a "Port assignment" behavior of "Port
overloading" for TCP
is too stringent, as proved in my earlier message and in the
draft-ietf-behave-requirements-update-00, and not needed.

Port overloading is perfectly acceptable when the remote endpoints are
distinct, as it preserves the uniqueness of the 5-tuple.

As a result, REQ-7 must be corrected.



-- 
_Ivan Chollet_