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New Member

Cisco 1841 Router

I have 1841 Cisco router. Today instalaltion of 2 MBPS leased line is done by ISP. I bought 1 WIC1-T card, From Loop I'll terminate V.35 cable in to serial port of router. I want to know if i need to do NATing. Is it neccesary?

What is i assign IP given to me by ISP on serial 0/0 int with encapsualtion commanda and for internal, i go for 192.168 range which i'll asssign on fa0/0

interface. I wonder why i need NATing ?


Amey Abhyankar.

Cisco Employee

Re: Cisco 1841 Router


Your local LAN is 192.168.x.x which is unregistered private addresses. These addresses are not routable on the internet. So, in order for these addresses to be routable in the internet, they need to get a public ip address or routable ip address.

So, in your case you would want to configure NAT on the 1841, so the 192.168.x.x addresses will get translated to a routable ip address when they want to go to the internet. If you are getting only one Public IP Address from your ISP, then you can configure Port Address Translation.

NAT also provides security, by hiding the internal address.

I am also enclosing the FAQ and overview links for NAT which should answer most of your question.

Let me know if it helps.



New Member

Re: Cisco 1841 Router

Thanx for the quick reply. I got 32 public IP's for WAN interface & 16 public IP's for lan. But i think assigning public IP's directly to machines is not a best practice..May be hackers can enter. As you mentioned i'll be going for NAT. Internal private IP range will remain as it is and public IP's i received from ISP will be used in NATing. "NAT also provides security, by hiding the internal address. " <<< This is my

requirement. I never tried NATing. But i hope

it wont be a difficult issue. 1841 rouuter has

some advanced features like cryptography feature and IDS detection. You ever configured

these options? I am curious to know.

Thanx & Regard's,

Amey Abhyankar.

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