Thai Pepper. Nazih Haddad This person is a verified professional. Verify your account to enable IT peers to see that you are a professional. Short answer is: Routing - rules that guide what source traffic will pass unto a destination point, and then your have routing protocols that work out what networks can be reached around it so make decisions as to where a data packet should be sent.
Such questions make more sense when his profile doesn't show him as CCNA certified anymore. JKintz79 This person is a verified professional. Wow, now you're a stalker Hope becki doesn't show up as well.
Sorry me too. I just couldn't help it. So sorry. Won't happen again. Cheers, Pieter. System I. T May 2, at UTC. I think we have it covered everyone from the first 5 posts Also, it does the translation of port numbers i.
NAT generally operates on a router or firewall. When a packet traverse outside the local inside network, then NAT converts that local private IP address to a global public IP address.
When a packet enters the local network, the global public IP address is converted to a local private IP address. If NAT runs out of addresses, i. Why mask port numbers? Suppose, in a network, two hosts A and B are connected. Now, both of them request for the same destination, on the same port number, say , on the host side, at the same time. Destination will send replies to the public IP address of the router. Thus, on receiving a reply, it will be unclear to NAT as to which reply belongs to which host because source port numbers for both A and B are the same.
NAT inside and outside addresses — Inside refers to the addresses which must be translated. Outside refers to the addresses which are not in control of an organization. These are the network Addresses in which the translation of the addresses will be done. Skip to content. Change Language. In addition to giving users more control over how NAT addresses are used, the Rate-Limiting NAT Translation feature can be used to limit the effects of viruses, worms, and denial-of-service attacks. Static route entry is configured in the next-hop router and redistributed within the routing network.
When the inside global address is matched with the local interface, NAT installs an IP alias and an ARP entry, in which case the router will proxy-arp for these addresses. If this behavior is not wanted, use the no-alias keyword.
When a NAT pool is configured, the add-route option can be used for automatic route injection. As a result, 10, translations more than would generally be handled on a single router consume about 3 MB. Therefore, typical routing hardware has more than enough memory to support thousands of NAT translations. For The current session is not maintained when failure takes place. Encapsulation does not matter for NAT. There must be an inside and an outside for NAT to function.
This can be accomplished through the use of an access list describing the set of hosts or networks that require NAT. All sessions on the same host will be either translated or will pass through the router and not be translated. Access lists, extended access lists, and route maps can be used to define rules by which IP devices get translated. The network address and appropriate subnet mask should always be specified.
The keyword any should not be used in place of the network address or subnet mask. PAT overloading divides the available ports per global IP address into three ranges: , , and It attempts to assign the same port value of the original request, but if the original source port has already been used, it starts scanning from the beginning of the particular port range to find the first available port and assigns it to the conversation. There is an exception for To define a pool, the configuration command is used:.
The following example translates between inside hosts addressed from either the In the following example, the goal is to define a virtual address, connections to which are distributed among a set of real hosts. The pool defines the addresses of the real hosts. The access list defines the virtual address. If a translation does not already exist, TCP packets from serial interface 0 the outside interface whose destination matches the access list are translated to an address from the pool.
In practical use, the maximum number of configurable IP pools is limited by the amount of available DRAM in the particular router. Cisco recommends that you configure a pool size of Each pool should be no more than 16 bits.
In This has limited NAT to only have a maximum of pools. It also has the capability to map a single inside IP address to different Inside Global addresses based on the rule. IP address overlapping refers to a situation where two locations that want to interconnect are both using the same IP address scheme.
This is not an unusual occurrence; it often happens when companies merge or are acquired. Without special support, the two locations will not be able to connect and establish sessions. The overlapped IP address can be a public address assigned to another company, a private address assigned to another company, or can come from the range of private addresses as defined in RFC Private IP addresses are unroutable and require NAT translations to allow connections to the outside world.
The solution involves intercepting Domain Name System DNS name-query responses from the outside to the inside, setting up a translation for the outside address, and fixing up the DNS response before forwarding it to the inside host. A DNS server is required to be involved on both sides of the NAT device to resolve users wanting to have connection between both networks.
Static NAT translations have one-to-one mapping between local and global addresses. Users can also configure static address translations to the port level, and use the remainder of the IP address for other translations. The following example shows how to configure routemap to allow outside-to-inside translation for static NAT:. NAT overloading is PAT, which involves using a pool with a range of one or more addresses or using an interface IP address in combination with the port.
When you overload, you create a fully extended translation. Unique source port numbers on each translation are used to distinguish between the conversations.
In dynamic NAT translations, the users can establish dynamic mapping between local and global addresses. Dynamic mapping is accomplished by defining the local addresses to be translated and the pool of addresses or interface IP address from which to allocate global addresses and associating the two. All the public IP addresses need to be unique.
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