Subject: [NAT] Re: Clarification on Twice NAT

From: "Rajendra Prasad" <[email-masked]>
Date: 28 Mar 2002 13:54:29 -0000

Hi,

  I am implementing Twice NAT according to RFC 2663 and RFC 
2694.

  I have a doubt in the implementation of Twice NAT.

Assuming that the Overlapping network address is 20.0.0.0, and the 
temporary local address is  from 10.0.0.0.

If a packet comes from Valid 20.0.0.0 network to the overlappped 
network,

1) When should we apply the Twice NAT, i.e should we do it after 
the Route Look-up or before the Route look-up.

1a) Assuming that we do the Translation first and then the route 
lookup, the scenario will be as follows for an Outbound Pkt.

before twice NAT translation -

Source address 20.1.1.1
Destination    10.1.1.1

After Twice NAT Translation -

Source address 20.1.1.1
Destination    20.1.1.1

If I do the route lookup now with the destination address as
20.1.1.1, the packet will again go to the Local Network.

1b) Assuming that we do the route lookup first and the Translation 
next, the scenario will be as follows for an Outbound Pkt.

before twice NAT translation -

Source address 20.1.1.1
Destination    10.1.1.1

If I do the route lookup now with the destination address as 
10.1.1.1, since this is a temporary address which is known to NAT, 
it will not be present in Routing Table.
    If we add a static route, what should be the gateway for 
10.1.1.1? Or should should we have a default Route?

Please do clarify this,

Thanks

B.Rajendra Prasad

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From: "Rajendra Prasad" <[email-masked]>
Date: 28 Mar 2002 13:54:29 -0000

Hi,

Source address 20.1.1.1
Destination    10.1.1.1

Source address 20.1.1.1
Destination    20.1.1.1

Source address 20.1.1.1
Destination    10.1.1.1

Please do clarify this,

Thanks

B.Rajendra Prasad