Is this possible with NAT?

Answered Question
Nov 30th, 2009

First of all, it's been quite a while since I've been on the boards, and WOW, it's changed.

Now to my question. I have a device that needs certain ports forwarded to it, but I'll have another device that will need the same ports forwarded as well. I'm not sure how I'll be able to handle this. Currently, I have:

ip nat inside source static udp 10.20.1.40 1254 interface FastEthernet4 1254

I'll also need the same port forwarded to another address on a different subnet, but I think the router is going to get confused since there's only one public address. I've got an acl on Fa4 that allows these ports in, but it's not "opening" up to any device on the inside. Any other suggestions to get this to work?

I don't have the option for another public address, or that would solve all of my problems. :-(

Thanks!

John

I have this problem too.
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Correct Answer by Jon Marshall about 7 years 1 week ago

j.blakley wrote:

First of all, it's been quite a while since I've been on the boards, and WOW, it's changed.

Now to my question. I have a device that needs certain ports forwarded to it, but I'll have another device that will need the same ports forwarded as well. I'm not sure how I'll be able to handle this. Currently, I have:

ip nat inside source static udp 10.20.1.40 1254 interface FastEthernet4 1254

I'll also need the same port forwarded to another address on a different subnet, but I think the router is going to get confused since there's only one public address. I've got an acl on Fa4 that allows these ports in, but it's not "opening" up to any device on the inside. Any other suggestions to get this to work?

I don't have the option for another public address, or that would solve all of my problems. :-(

Thanks!

John

John

Yes, it's quite different from the old NetPro

Short answer to your question is you can't. The router would have no way of knowing which address to forward it to. The only thing you can do is run the service on a different port on one of the devices and then you can do a different port forward translation. This is fine if it is for one or two external clients connecting to the device because you can tell them to change the port but obviously with a web server accessed from the internet it is completely impractical.

Jon

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Correct Answer
Jon Marshall Mon, 11/30/2009 - 10:54

j.blakley wrote:

First of all, it's been quite a while since I've been on the boards, and WOW, it's changed.

Now to my question. I have a device that needs certain ports forwarded to it, but I'll have another device that will need the same ports forwarded as well. I'm not sure how I'll be able to handle this. Currently, I have:

ip nat inside source static udp 10.20.1.40 1254 interface FastEthernet4 1254

I'll also need the same port forwarded to another address on a different subnet, but I think the router is going to get confused since there's only one public address. I've got an acl on Fa4 that allows these ports in, but it's not "opening" up to any device on the inside. Any other suggestions to get this to work?

I don't have the option for another public address, or that would solve all of my problems. :-(

Thanks!

John

John

Yes, it's quite different from the old NetPro

Short answer to your question is you can't. The router would have no way of knowing which address to forward it to. The only thing you can do is run the service on a different port on one of the devices and then you can do a different port forward translation. This is fine if it is for one or two external clients connecting to the device because you can tell them to change the port but obviously with a web server accessed from the internet it is completely impractical.

Jon

John Blakley Mon, 11/30/2009 - 11:14

Well, that's what I thought. Okay, so here's my problem

I have an 871W. I run an XBox 360 behind it, and it has to have open NAT to operate correctly. I bought another XBox for my son for Christmas, and I'm going to need to set this one up different because he connects to an ASA on a different subnet (yeah, it's all in my house). So, it looks like:

   871W

     |  |

ASA Xbox360 (mine)

    |

Xbox360 (his)

I'm not sure the best way to set the 360 up. If I have the ports just opened, then it says it's "Strict NAT", but if I port forward, then all is good. I'm wondering if this other Xbox is going to work online, OR if I need to replace my Cisco with a Linksys that supports UPnP or something.

Anyone out there with two Xbox's behind their router?

Giuseppe Larosa Mon, 11/30/2009 - 11:21

Hello John,

>> yeah, it's all in my house

what a big house you have and safe (from a networking point of view) 

Best Regards

Giuseppe

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