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Pix failed, please help configure cisco 2524

Posted on 2006-05-19
Medium Priority
Last Modified: 2010-03-19
I have/had a setup similar to:

              ____________                  _________            ________
            |                     |                |               |           |             |=======computer1
   T1 ==|  cisco 2500    |=======|  PIX 506  | ==== |  hub      |=======computer2...
            |____________|                |________ |           |________|=======computerN

The problem is that the PIX firewall has failed/died.  Now nothing is doing the NAT or DHCP.  
I would like to assign these functions to the Cisco 2524 if this is possible.  I have the rollover cable and have succeeded in reseting the password which no one knew, using Hyperterminal and the console.
I do not know how to configure this router to act as a T1 transceiver/modem and provide NAT and DHCP to about 15 computers using the console or any other way for that matter.  Could somebody provide me with a guide, URL or whatever (an idiot guide) so that I can get things up and running until we decide on the firewall situation.  For instance what's the difference between configureing ethernet and serial and which one do I configure for IP?
I have no documentation other than the PDF available at cisco, but this does not explain the terminology you are faced with when configuring the router via the terminal emulator.
I know all the IP addresses and subnetting but can not tell whether I am entering information for the WAN or the LAN since the console provides no feedback in this regard.

Any help is greatly appreciated..

Question by:lizardqueen007
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LVL 11

Accepted Solution

prueconsulting earned 540 total points
ID: 16720525
It depends on the IOS version running on the router if its capable of providing nat functionality or not.

If it is capable of natting then you would just enter the command

ip nat inside in the internal interface(eth0)  
ip nat outside on the external interface (serial 0 most likely)

http://www.cisco.com/en/US/products/sw/iosswrel/ps1839/products_feature_guide09186a0080087bac.html for an example
LVL 11

Expert Comment

ID: 16720531
Of course i forgot.. This is when in configuration mode

conf t
interface serial 0
ip nat outside
interface fastethernet 0
ip nat inside

Author Comment

ID: 16720710
Thankyou for fast!
Is there a way to check ios to see if capable perhaps a list of compatability or something?
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LVL 11

Expert Comment

ID: 16720811
One quick way is to login to the router and try and issue the command do a ip ? and see if ip nat is an available option..

Issue the command and see if it says unrecognized command.

If it does then chances are you might require a firewall IOS to do the nat'ting..
LVL 79

Assisted Solution

lrmoore earned 480 total points
ID: 16720980
Capture output of
router>show version

You many not have the ability to be a DHCP server and may not have enough dram/flash memory to even upgrade the IOS to provide that service. You 'should' be able to do the nat, though..

Adding to prueconsulting's example above:

router#config term
router(config)#interface Ethernet0
router(config-if))#ip address secondary
router(config-if))#ip nat inside
router(config)#access-list 1 permit
router(config)#ip nat inside source list 1 interface Serial0 overload
router(config)#interface serial0
router(config-if)#ip nat outside
router#write mem

Then manually assign IP addresses to the workstations using 192.168.169.x / 24

You might want to reconsider and just run out to the local office supply store and buy yourself a little $50 Linksys/Dlink broadband router. It does nat and dhcp right out of the box.

LVL 28

Assisted Solution

mikebernhardt earned 480 total points
ID: 16721034
First of all, here is a basic config guide:

But in order to have a complete config guide, you need to tell us what version of IOS it's running. The output of "show version" will give you that. NAT should be supported in any version. But DHCP may not be, depending on the IOS version again.

The serial interface should not need to be touched except for adding "ip nat outside" as mentioned earlier.
The ethernet interface will need to have the correct ip address added. This should be the LAN's default gateway address, for example:
ip address
ip nat inside

It's not quite as simple to configure it for nat as prueconsulting told you. You also have to tell it what to do about NAT. Assuming that the above is your LAN addressing:

ip nat inside source list 1 serial0 overload
access-list 1 permit

This will take any ip on the LAN and translate it to the serial 0 address.
LVL 28

Expert Comment

ID: 16721057
Oops, looks like lrmoore and I said the same thing. I agree with hime on the Dinky brand router as well, it will be a lot easier to work with until you get your PIX replaced- just configure the Dinky's WAN address to talk to whatever address is on the ethernet port of the 2524 and everything else should pretty much take care of itself.
LVL 28

Expert Comment

ID: 16721065
But don't go looking in Best Buy for a brand called "Dinky" though :-)
LVL 79

Expert Comment

ID: 16722054
D-Link / Linsys = Dinksys = Dinky! I like it!

Author Comment

ID: 16747433
Thank you everyone,
I really appreciate the quick responses and I'm sure that your answers were good, but I'm glad that I did not have to put them all to the test this time.  I split the points, because I was unable to test each response individually.  Luckily the Pix turned out to be ok and was not the problem.  The crossover cable was the problem, which I should have tested first.    Irmoore: The problem with using a linksys or dlink is that I required a T1 adapter.  FYI I realized that the lack of link light (which I did not disclose-sorry) was due to the crossover and I mistakenly jumped to the conclusion that it was the PIX malfunctioning.  In an attempt to reset the password to the router, I over wrote the router and had to complete the configuration.  Luckily I found a person at Qwest (very helpful) that was able to talk me through the configuration and had the necessary IP information to finish the job.  I will take some personal time to work with a cisco 2500 router and a pix to become more familiar with the hyperterminal interface, because for someone who has never used it, learning how to use it under fire is not fun.  I will eventually have to reset the PIX password on this setup I'm afraid, since the last IT person left without documentation.  Thanks again everyone.

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