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Gaining access through a Cisco 678 & Linksys DSL/Cable router

Posted on 2002-06-04
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Last Modified: 2010-04-17
I have been trying to get access to my office network network for a few weeks now without any luck.  Here's the scenario:

I have a Cisco 678 using Qwest DSL.  I have a block of static IPs.  I have a Linksys DSL/Cable router behind the Cisco.  The internal IP to my Linksys is 192.168.0.1 and the computer that I want access to is 192.168.0.21 and the program I'm using on that computer uses port 1387.

I have already added the following line to my Cisco 678:

set nat entry add 192.168.0.1

I first tried "set nat entry add 192.168.0.21" but after I though about it, I would like to pass all ports through the Cisco to the Linksys.  Then allow the Linksys to block all ports except for 1387.  I want to block all ports, excluding port 1387--sending this traffic to IP 192.168.0.21.

Let me know if there's a better way to go about this or what I'm doing wrong.  Thanks!
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Question by:kendalltech
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by:geoffryn
ID: 7056522
Turn off NAT on the Cisco and pass all the traffic to the Linksys and NAT it there.
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by:t1n0m3n
ID: 7058273
the only problem with that is your inside ethernet on the 678 and the outside ethernet on your linksys has to be public addresses.  If your ISP is DHCP then this will be difficult.

A better answer would be to use a on to one NAT (as opposed to PAT) on the 192.168.0.1 address to the outside interface of the 678 and then use port forwarding on the linksys to forward the packets to the machine that you want to send the packets to.  (Or use the DMZ option to put the entire machine directly on the internet.)
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by:kendalltech
ID: 7059289
Thanks for the suggestions.  I will try it today.  I'm not sure how to do a one to one NAT but I have not disabled NAT.  On another network that I'm trying the same thing, I told the customer that his DSL had to have a static IP address and I configured the Cisco for a static IP and it worked fine.  So, maybe the DHCP and or NAT is a problem?  But, it seems that the same IP address is assigned day after day.
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scraig84 earned 150 total points
ID: 7062003
One to one NAT is not possible on a 678.  The 678 only supports PAT.  I am assuming if you want to perform any type of inbound NAT/PAT on either the 678 or the Linksys that you have been give a static public range by the ISP.  If this is true, simply turn off NAT on the 678, give the Ethernet interface on the 678 to be the same as the WAN address, give the Linksys WAN interface another address from the pool given to you by the ISP and point it's default gateway at the new Ethernet address on the 678.  I know it seems weird to give the Ethernet the same IP as the WAN, but that's how these things work.  

Here is Qwest's basic config for customers with static IP addresses:

http://w3.webaccess.net/support/instructions/qdsl/qwest_dsl_info_sheet-static.pdf

Hope that helps.
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