Cisco 1841 for Static NAT

[rcamburn]

Hello! I need guidance in establishing a Static NAT on an 1841 router.

I'm at a FOX affiliate TV station, and in order to connect our EAS Device to the internet & Fox Splicer, I need

to setup a Statio NAT, so we picked up an 1841 on eBay.

I've done a little configuration in HyperTerminal.

I've done these ip addresses:

FE0/0 10.1.10.13        this is the subnet our EAS device is on

FE0/1 10.110.81.174   this is the subnet of the Fox Splicer.

I need to have NAT translate 10.1.10.11 to 10.110.81.170 and I also need to set a route

for 10.110.81.0/24 pointing to 10.110.81.161

I'm a Television Engineer, not a Network Engineer, but I'm not afraid to push buttons & break things!

Thanks in advance & have a great day!

Rick

[Reza Sharifi]

Hi,

Usually, you use NAT to go from private IPs to public and vice versa.  In your case, these IPs are all private and there is no need for NAT here. So, you need to find out the public (Internet) address you need to translate your private IPs to.

HTH

[rcamburn]

Thanks for the reply,

I need to translate 10.1.10.11(IP address of EAS device) to 10.110.81.170(address the Fox Splicer is expecting

the EAS device to be)

Thanks again!

Rick

[bobmccouch]

Hi Rick,

So the Fox Splicer is expecting the EAS device to be at 10.110.81.170. Does the EAS device know that the Fox device is at 10.110.81.X, or does it likewise believe that the Fox device is on its subnet of 10.1.10.0/24?

If the EAS device knows the real IP of the Fox device and just needs to show up in the 10.110.81.170 network when it talks to the Fox device, it should be as simple as:

int fa0/0

ip nat inside

!

int fa0/1

ip nat outside

!

ip nat inside source static 10.1.10.11 10.110.81.170

If your router has an interface in the 10.110.81.0/24 network, it doesn't need an explicit route to it, as it will see that entire network as connected.

However, how does the EAS device know to go to 10.1.0.13 in order to reach the Fox splicer? If the router is the EAS device's default gateway, you're all set but if not (if the 1841 is just present on the EAS device's LAN but isn't the default gateway) then you may need that second case where the router makes each device appear to be on the other subnet and the configuration is a little more complex.

Hope this helps. Post back if you need to solve that second case.

[rcamburn]

Thanks for the reply,

The EAS device does not know to go to 10.1.0.13 in order to reach the Fox Splicer.

The EAS is connected to a simple 4-port router, that is connected to a Comcast modem, 10.1.10.1

This is the connection the EAS device needs to receive Common Alert Protocol(CAP) messages

from apps.fema.gov, as mandated by the FCC.

Another connection from the 4-port router will go the Fox Splicer. This connection is how the Splicer

gets xml data from the EAS to generate alert crawls.

Before this FCC mandated CAP Compliance, we just had the EAS IP set to 10.110.81.170

I've been looking through the interwebs for some "NAT for Dummies" guidance, as its taken me 3 days just

to figure how to get to a command line interface by means of HyperTerminal on XP.

If ever there was a time that I felt smart, it sure wasn't this week.

If this can't be accomplished, the EAS device manufacturer has told me that they will eventually release a firmware

that will support a USB to IP adapter that would give us the needed dual-nic connectivity.

Thanks again!

Rick

[bobmccouch]

OK, so the two devices used to be on the same subnet, now they're not and they still need to think they're on a common subnet since they're default gateways don't know how to reach each other, right?

You could solve this with routing, potentially, or with the 2-way NAT I mentioned before.

It may be easiest to do this using the NVI (NAT virtual interface) feature. Or else with both an inside static NAT and an outside static NAT along with a required static route.


Sent from Cisco Technical Support iPhone App

[bobmccouch]

Hi Rick,

I played around in my lab and worked up what I think you need. I created two networks, A (10.1.10.0/24) and B (10.110.81.0/24) and two hosts, HostA (the "EAS device") at 10.1.10.11, and HostB (the Splicer) at 10.110.81.161 (I think this was right based on your original post). In the middle I put my router, which is connected to both subnets but is not the default gateway for either. I used the following config:

interface FastEthernet0/0

ip address 10.1.10.13 255.255.255.0

ip nat enable

!

interface FastEthernet0/1

ip address 10.110.81.174 255.255.255.0

ip nat enable

!

ip nat source static 10.110.81.161 10.1.10.161

ip nat source static 10.1.10.11 10.110.81.170

Note the use of the "ip nat enable" command rather than the "ip nat inside" or "ip nat outside" commands that I mentioned preivously. This activates the NVI feature I mentioned which makes life easier when doing 2-way NAT like this.

The result is, I think, what you are looking for. The "EAS device" host thinks the "Splicer" is on its local subnet, with IP address 10.1.10.161. The "Splicer" thinks the "EAS device" is on its local subnet, at 10.110.81.170. Neither host realizes the other is not directly connected to its subnet, and no routing setup, static routes, or changes to default gateways are required.

Hope this is helpful. Good luck!

Bob McCouch
CCIE #38296 (Routing & Switching)

[rcamburn]

Hi Bob!

Sorry for the delay in my response, I had to reset my password & wait....

I'm going to attempt to make these configuration changes you suggested today,

Its a slow process, as I'm looking up how to do things, as I need to these things....

I'll post what I come up with,

Thanks again!

Rick

[rcamburn]

Hi Bob, I tried what you suggested & it does not seem to work.

I have attached a diagram provided to me from Fox of how this is supposed to work,

with the IP addresses we would be using here.

Thanks again for any & all of your help!

Rick

[bobmccouch]

Hi Rick,

Well, to meet the exact requirements of that doc you could use the first config bits I posted (You'll have to remove any other NAT related config first):

int fa0/0

ip nat inside

!

int fa0/1

ip nat outside

!

ip nat inside source static 10.1.10.11 10.110.81.170

But doing that you'd just have to have a way to tell the EAS device how to reach your Splicer or else it would probably go to the Comcast router for default and it would never find its way back to the Splicer. Perhaps there is a static route configuration in the EAS device or something.

The diagram's note to "Set route for 10.110.81.0/24 to 10.110.81.161" on the router doesn't really make any sense, as the router would see the 10.110.81.0/24 network as "connected" and ignore any static route for the same prefix. Did whoever designed this solution provide you those values, or did you interpret that from another piece of info? It just doesn't seem to make a lot of sense so I'm wondering if that's the missing piece here.

What you're trying to accomplish shouldn't be hard, just a matter of understanding the requirements and the existing configuration.

Best Regards,
Bob McCouch
CCIE #38296 (Routing & Switching)

-------------------------------------------
Please note: Any recommendations or advice provided in my posts are made with the best of intentions and are believed to be accurate and correct, however no warranty is provided nor will any liability be assumed for any result of following these recommendations or advice.

[rcamburn]

Hi Bob,

Yes, there are settings in the EAS Device configuration that knows to send data to the to DCMs, 10.110.81.198 &

10.110.81.121

The information for setting a route for 10.110.81.0/24 to 10.110.81.161 was provided by Fox, they say this is how they

have set up other affiliates.

I will spend more time on this again tuesday & post back what I find.

Thanks again!

Rick

[bobmccouch]

Hi Rick,

If the EAS device knows that it has to send packets meant for the DCMs to 10.1.10.13, as opposed to the default gateway it uses for everything else (I'd assume 10.1.10.1 -- the Comcast router's LAN interface) then you should be all set with that original NAT I suggested.

Good luck. Let me know what you find out.

PS- The consulting company I work for does work for another TV station. If you need some networking expertise on tap in an official capacity, let me know.

[Reza Sharifi]

Rick,

You can use one of the scenarios in this link to start. In your case, fe0/0 is inside and fe0/1 is outside interface.

http://www.cisco.com/en/US/tech/tk648/tk361/technologies_tech_note09186a0080094e77.shtml

HTH