From: Edwards, Andrew M (andrew.m.edwards@boeing.com)
Date: Fri Apr 09 2004 - 13:41:55 GMT-3
Here's another way of looking at it with an
Ip nat outside source list command.
http://www.cisco.com/en/US/tech/tk648/tk361/technologies_configuration_e
xample09186a0080093f8e.shtml
-----Original Message-----
From: David Hiers [mailto:David_Hiers@adp.com]
Sent: Friday, April 09, 2004 8:37 AM
To: ccielab@groupstudy.com
Subject: RE: Restated question: NAT and ip routing sequence order
Hi,
ip nat inside vs outside seems to matter:
http://www.cisco.com/warp/public/556/5.html
David
-----Original Message-----
From: David Hurtado [mailto:dei2viccie@hotmail.com]
Sent: Friday, April 09, 2004 7:13 AM
To: Guy.Lupi@eurekanetworks.net; ccielab@groupstudy.com
Subject: Restated question: NAT and ip routing sequence order
Maybe i didn't state my question clearly. Sorry.
Suppose you implement NAT in a router. You establish a NAT inside
interface
and a NAT outside interface. The link that i mentioned before says that
a
packet that goes from inside interface to outside interface will be:
1:. Routed by the routing process.
2: Translated by NAT
And that a packet that goes from outside interface to inside interface
will
be:
1:. Translated by NAT
2:. Routed by the routing process.
What i wanted to know is if:
-the rule applies only to routers configured with "ip nat inside"
statement
OR
-the rule applies to whatever router that implements NAT (doesn't matter
that it is configured with "ip nat inside" or "ip nat outside"
statement)
I think this topic is interesting because suppose you have a router with
3
interfaces:
NO NAT ----E0/1 (ROUTER) E0/2 ------- NAT INSIDE
E0/3
|
|
NAT OUTSIDE
You implement "ip nat inside source" translation and "ip nat outside
source"
translation:
If you send a packet from NAT inside:
1: Routing process will decide where to send the packet
2: A.-If the destination interface is NAT outside, the address will be
translated
2:B - If the destination interface is NO NAT interface, the address will
NOT
be translated
If you send a packet from NAT outside:
1: NAT will translated the packet (doesn't matter which will be the
output
interface)
2: Routing process will decide where to send the packet
So a packet coming into the router from the outside interface will
ALWAYS be
translated!!!!
This is what i deduce from the statement in:
http://www.cisco.com/en/US/tech/tk648/tk361/technologies_tech_note09186a
0080
094430.shtml
Probably i'm wrong, but i hope that somebody could explain which is the
sequence of actions in function of the NAT configuration
Sorry again for the above email.
Thanks
>From: "Lupi, Guy" <Guy.Lupi@eurekanetworks.net>
>Reply-To: "Lupi, Guy" <Guy.Lupi@eurekanetworks.net>
>To: "'David Hurtado'" <dei2viccie@hotmail.com>, ccielab@groupstudy.com
>Subject: RE: NAT and ip routing sequence order
>Date: Fri, 9 Apr 2004 09:57:42 -0400
>
>The only way for NAT to function is to have at least one inside and one
>outside interface, so if you have NAT running on a router you will
>always have an interface with the "ip nat inside" statement on it.
>
>This doesn't apply at all if there is no NAT on the router, or perhaps
>I am not understanding your question?
>
>-----Original Message-----
>From: David Hurtado [mailto:dei2viccie@hotmail.com]
>Sent: Friday, April 09, 2004 8:51 AM
>To: ccielab@groupstudy.com
>Subject: NAT and ip routing sequence order
>
>
>Hello everybody,
>
>Reviewing the following link:
>
>http://www.cisco.com/en/US/tech/tk648/tk361/technologies_tech_note09186
>a0080
>094430.shtml
>
>I have read this statement:
>
>Note: When a packet is going from inside to outside, it is routed and
>then translated (NAT). In the opposite direction (outside to inside),
>NAT takes place first.
>
>Is it always valid or is only applicable to "ip nat inside"?
>
>Thanks for the help
>
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