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Webcast-Catalyst9k
New Member

Addressing and NAT

Plain and simple I guess. Do I need more than a /30 on a router to telnet to it if it is running NAT?

I have two routers connected by a t1 with a /30 between them. I configured NAT on the LAN side of one, but now I cannot telnet to it I think because it is trying to get to the pc instead of the router. Is this correct?

6 REPLIES
New Member

Re: Addressing and NAT

You should be able to telnet from one router to another but if you are trying to telnet from one router to a pc on the remote routers network, then it should not work. If you had more available IP's then you could static NAT a IP to the PC. Then you could telnet from the outside to the PC

New Member

Re: Addressing and NAT

I still can't telnet to it, but I can ping it.

If there is a pc behind the router with a private address and I were to ping the public address, doesn't the router and NAT forward the ping requests to the pc or does the router respond?

New Member

Re: Addressing and NAT

If i guess correctly u have the topology as follows

PC---------------R1-----------------------R2

Now you have applied NAT on the lan side that towards the PC.

The network is now the public ip address which you have given in the NAT translation.

If you ping or telnet this public ip address from R2 side, you should be able to ping or telnet.

but if you ping or telnet to the local address which is translated, then you could not succeed in that, coz, you have masked it using the public ip address.

this has nothing to do with /30 mask. you can overload the interface in natting.

-Deepak

Silver

Re: Addressing and NAT

Just as mentioned, this has nothing to do with a /30 mask. but if you try to telnet into the router with the NATted address, it might not go depending on your NATting configuration. You should realise that the NATted address is not born by any system, unless you are NATting to an interface address. Hence, you will normally not be able to telnet into it. The workaround is to configure Static NAT simultaeneously and redirect port 23 to the router.

New Member

Re: Addressing and NAT

I believe that this last message is the case. I have NAT'd the one public address and overloaded it and I cannot connect (telnet) to that address on the router.

Could you please explain or give and example of the static NAT and port redirect? Thanks

Silver

Re: Addressing and NAT

You could configure NATting using the following command

ip nat inside source list 1 interface loopback 0 to nat to an interface

or configure simultaeneously static and dynamic NATing

Check out the following link

http://www.cisco.com/en/US/tech/tk648/tk361/technologies_tech_note09186a0080093f31.shtml

hope it helps

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