• How to Configure NAT and PAT on a Cisco Router

      6 comments

    When would you need this: When you want to connect a local network to the Internet and you don’t have that much IP addresses.

    Special Requirements: None.

    There are two types of NAT that can be configured on a Cisco router; static, and dynamic.

     Static NAT Configuration:
     This type is used when you want to do one-to-one assignment of local IP addresses to global IP addresses.
     1. Establish static translation between an inside local address and an inside global address,
     Router(config)#ip nat inside source static XXX.XXX.XXX.XXX YYY.YYY.YYY.YYY
     where,
     XXX.XXX.XXX.XXX is the (inside) local address
     YYY.YYY.YYY.YYY is the (inside) global address
     
    2. Specify the local interface. This is done by going to the interface configuration mode and issuing,
     Router(config-if)#ip nat inside
     

    3. Specify the global address. This is done by going to the interface configuration mode and issuing,

     Router(config-if)#ip nat outside
     

    Dynamic NAT Configuration:

     This type is used when you want the router to do the mapping dynamically. This method is useful when you have too many global and local addresses and you do not want to do the mapping manually, or when the number of global addresses available is less than the local addresses.
    This would lead us to two different scenarios,
    A. The number of global IP addresses is equal or less than the local addresses and more than one. (global >= local >1)
    1. Define a pool of global addresses that would be employed in the translation,
    Router(config)#ip nat pool NAME XXX.XXX.XXX.XXX YYY.YYY.YYY.YYY netmask ZZZ.ZZZ.ZZZ.ZZZ
    where,
    NAME is the name of the pool
    XXX.XXX.XXX.XXX is the starting IP address of the pool
    YYY.YYY.YYY.YYY is the end IP address of the pool
    ZZZ.ZZZ.ZZZ.ZZZ is the subnet mask of the network that the pool is part of.
     
     

     

     

    Read the rest of the article in the Router Geek Book: Guide to Cisco Routers Configuration

     
    • Hi,

      I have a SIP PBX in my LAN.
      I have just 2 IP addresses. 1 for the router and 1 is assigned to the VPN router.

      I want to use SIP Clients from the internet to access my SIP PBX gateway which is on the LAN.

      Is there any way I can achieve this?

      I tried creating 2 VPN clients, registering them. However there is a problem when 2 VPN-client connected SIP users talk to each other. There is no speech between the two SIP clients. looks like the rtp packets are not transported properly. I am using a Planet MH3400 router. WAN router is CISCO887-k9.

    • explained clear as crystal..

      thank you so much…

    • Why can’t our Cisco Netacad be this concise and clear? Thanks

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