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NAT configuration on CISCO 1750

Posted on 2003-03-03
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Last Modified: 2010-08-05
Hi All,

I would like to configure NAT on my cisco 1750.
(I want to enable my local system with a public address.)

1. How can I assign two ip address (Public & Local ) for the same interface on the router.?
2. How can I configure the NAT for my local system on the router?

Thanks in Advance.

Regards,
Gopu
Email : gopu@siptech.co.in
System Administrator,
SIP Tech,
INDIA.
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Question by:ngopu
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by:pedrow
ID: 8062579
Shall we assume that you're only going to use the Fast Ethernet interface and not utilize any serial ports on the router?

If you're just gonna use the single FastE for your setup (boat-anchor), you'll have to configure the FastE with subinterfaces and use that as a trunk to go into a switch that supports VLANS.

This way what you're doing is creating logical 'inside' and 'outside' ports. If you've got the switch hardware available to go this route, let us know what kind of switch you've got, what version of IOS you're running (you neet at least the 'plus' feature set) and we can cook up some configs for you.

There may be another way to do it, but I can't think of it as NAT will want defined inside and outside ports...


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by:matt_t1
ID: 8064846
I'll back up Pedrow on this one - we've tried to think of a way round this before.

There is no way (that we could find) to define one interface as both the inside AND outside of NAT.  The most promising line of thought we came up with was to define a loopback interface to act as the outside - but then you run into overlapping address space and routing issues.

The way we went was as Pedrow suggests - 802.1q VLANs.  That way the router has multiple logical interfaces on the single physical pipe.

BUT...

Depending on what you're trying to achieve, do you actually need NAT?  It sounds like you are going to run 2 separate IP networks over the same Ethernet segment (not really a great idea, but lets say you've come down on this for a valid reason).

You can create a secondary address on the ethernet interface (ip address x.x.x.x x.x.x.x secondary), and the router will route packets in and out of the same interface.

But if the servers are on a LAN where they can see both the public and private networks directly, then why not just give each required server a second IP address in the public network?

I must stress again - there are many MANY reasons why you shouldn't do this, all related to security.  But from an IP standpoint it should work.
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by:lrmoore
ID: 8442627
G'day, ngopu
It has been 59 days since you posted this question.
Do you still need help? Have you received enough information?
Can you close out this question?
Ways to close questions: http://www.apollois.com/EE/Help/Closing_Questions.htm
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by:ngopu
ID: 8442897
Can I 've more help regarding this.....???
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Accepted Solution

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lrmoore earned 80 total points
ID: 8443882
There is a sample config here that answers both of your questions:
http://www.experts-exchange.com/Hardware/Routers/Q_20603097.html
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by:lrmoore
ID: 8725621
ngopu,
No comment has been added lately (43 days), so it's time to clean up this TA.
I will leave a recommendation in the Cleanup topic area for this question:

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PLEASE DO NOT ACCEPT THIS COMMENT AS AN ANSWER!

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lrmoore
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