ISP routable addresses

Jul 07, 2007 7 Replies
C

Hi all, we have a Cisco ADSL ISR 871, the problem we have is that the ip on the ADSL interface is dynamically assigned by BT. BT have also given us a block of 6 routable addresses. So currently we have a static nat something like:


ip nat inside source static 192.168.1.10 172.xx.xx.xx


192.168.1.10 is the server address. This works an email is being delivered to the server on port 25.


We have a problem in that we want the router to have the static address so we can terminate vpn, and then forward port 25 onto the server for email.


Any suggestions will be greatly appreciated.


Many thanks,


Craig.


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G

"corb" ha scritto nel messaggio news:J8Jji.29494$ snipped-for-privacy@newsfe2-gui.ntli.net...

Hi,

If I got it right and you have six registered addresses assigned, why not using them? ( i.e. assign one to a loopback interface of the router to terminate VPNs )

Regards, Gabriele

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C

Oh I got you. Can I also create a sub interface for additional IP addresses?

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B

You don't need the sub-interfaces, the additional addresses are handled by standard NAT. Only reason for the loopback is because VPN requires a physical interface.

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C

I see, so changing the loop back interface ip address will not effect any other operation?

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B

It will affect the IP that your users would connect to for VPN, but that would be it's only function.

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C

Thanks for all the info. I have had a look on the web would I be able to use:

ip address xxx.xxx.xxx.xxx 255.255.255.255 secondary

on the adsl interface to add a secondary IP address ?

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B

I've never used a secondary address on a dhcp interface. If the router takes the command I don't see why not, I would do BUKU testing on it tho. If it were my setup or one of my customers I would be using a loopback to accomplish the goals.

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