Subject: Re: [lisp] LISP-NAT Deployment - draft-ietf-lisp-introduction-00

From: [email-masked] (Noel Chiappa)
Date: Thu, 1 Nov 2012 22:22:32 -0400 (EDT)

> From: [email-masked]

    > In the third paragraph of Section 10.5.1, you mentioned

    >  "in addition, since LISP expects all incoming data traffic to be on a
    >   specific port, it was not possible to have multiple ETRs behind a
    >   single NAT (which normally would have only one global address to share,
    >   meaning port mapping would have to be used, except that... )"

    > Is something missing here?
    > Certainly there maybe scenarios such like two or more LISP MN connect
    > behind the same NAT, i.e. two or more ETRs behind a single NAT.

Maybe I am missing something, but if a NAT has two ETRs behind it, and if an
inbound UDP packet to destination port 4341 arrives at the NAT, how does the
NAT know which ETR to send the packet to?

(Since the destination IP address in the packet is that of the NAT, and port
4341 would be used for packets to either ETR.)

Even if you look at the sort host and port, that doesn't necessarily help,
because some source ITR could be sending packets to both ETRs, so packets to
either ETR could also have the identical source host/port.

In short, there's no way for the NAT to know which ETR the packet is for.

Note that there is a separate "NAT Traversal For LISP" document which
provides mechanisms to bypass all these issues.

	Noel

---

From: [email-masked]
Date: Fri, 2 Nov 2012 11:38:53 +0800

Hi Noel,

  My response is inline. Thank you.

> 4341 would be used for packets to either ETR.)

I don't understand very clearly.

Consider the scenario that two ETRs behind a single NAT.

When NAT establish states for ETRs who both send packets outbound, it 
could assign
different global IP addresses for them.

As a result, when NAT receives packets inbound, even though packets both 
have Destination
port 4341, their destination addresses are according to different ETRs.

Was there something I misunderstood?

Best Regards
Li Cheng

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