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RE: The ip nat optional extendable posted 09/12/2007
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Where did you get that extendable means overloading? I thought Alex said
"I was under the impression extendable keyword means the overloading PAT
router will try to map to the same port number where ever possible."

He didn't say extendable is same as overloading/PAT, extendable enxtends
the address translation to layer 4 ... Patting uses same layer 3 address
with random port numbers to detect who is who, extendable gives the
capability to nat layer 3 and layer 4 at the same time.

Many Thanks
 
Yemi Salau

-----Original Message-----
From: Prasad Shemrudkar (pshemrud) [mailto:pshemrud@xxxxxxxxx] 
Sent: Wednesday, September 12, 2007 1:30 PM
To: Salau, Yemi; Alex Steer; Laidlaw, Patrick A.; ccielab@xxxxxxxxxxxxxx
Subject: RE: The ip nat optional extendable

Guys,

If extendable is overloading then what is overloading? Does this mean
the even if I do not need PAT, the IOS will automatically PAT (by way of
using extendable option)?

TIA,
Prasad

-----Original Message-----
From: nobody@xxxxxxxxxxxxxx [mailto:nobody@xxxxxxxxxxxxxx] On Behalf Of
Salau, Yemi
Sent: Tuesday, September 11, 2007 2:04 PM
To: Alex Steer; Laidlaw, Patrick A.; ccielab@xxxxxxxxxxxxxx
Subject: RE: The ip nat optional extendable

Exactly Alex, extendable option extends NAT capability to port level
(Transport Layer) .... Even if you don't specify it on your ip nat line,
lovely ios adds it for you automatically. This does not necessarily have
to be same port though, so I can nat at both layer 3 and layer 4 .... In
a nut shell, I believe the extendable option "extends" translation
capability to layer 4.

So if I do "ip nat inside source static tcp 1.1.1.1 80 2.2.2.2 80", even
if I don't add the extendable option, ios adds it for you automatically,
and this can be seen clearly with "sh run I I ip nat"

Many Thanks
 
Yemi Salau

-----Original Message-----
From: nobody@xxxxxxxxxxxxxx [mailto:nobody@xxxxxxxxxxxxxx] On Behalf Of
Alex Steer
Sent: Monday, September 10, 2007 10:29 PM
To: Laidlaw, Patrick A.; ccielab@xxxxxxxxxxxxxx
Subject: RE: The ip nat optional extendable

I was under the impression extendable keyword means the overloading PAT
router will try to map to the same port number where ever possible.
Obviously this might not work often with say port 80 so it will just use
another port when it can't

-----Original Message-----
From: nobody@xxxxxxxxxxxxxx [mailto:nobody@xxxxxxxxxxxxxx] On Behalf Of
Laidlaw, Patrick A.
Sent: 10 September 2007 21:34
To: ccielab@xxxxxxxxxxxxxx
Subject: The ip nat optional extendable

So for all you smart guys out there I've got a question for you.

The optional command "extendable" has a definition on Cisco's website
extendable
(Optional) Extends the transmission. So what in the world does that
mean?  What does this optional command actually do for nat.

I've been looking and don't really see anything explaining how it helps
out NAT or what kind of situation you would or would not use it in.  I
know I've seen lots of examples with it in them and that it's needed in
many of them but why is it needed.

Patrick Laidlaw
E: patrick.laidlaw@xxxxxxx
w: www.wwt.com

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