Camada de rede

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Camada de Rede
Protocolos da Camada de Rede: IP v4 (ARP); IP v6 (ND); ICMP NAT – Network Address Translation Protocolos de Routing: RIP; OSPF Comandos: Ping; Traceroute; Route Print

Novembro, 2010



Fonte: acetatos Prof. Manuel Ricardo - FEUP

NAT



NAT/PAT
– By using a different port number for each user, the NAT device knows which client PC toroute the incoming packets to.

NAT
• Network address translation
– From Wikipedia, the free encyclopedia



In computer networking, network address translation (NAT) is the process of modifying network address information in datagram packet headers while in transit across a traffic routing device for the purpose of remapping a given address space into another.
Most often today, NAT isused in conjunction with network masquerading (or IP masquerading) which is a technique that hides an entire address space, usually consisting of private network addresses (RFC 1918), behind a single IP address in another, often public address space. This mechanism is implemented in a routing device that uses stateful translation tables to map the "hidden" addresses into a single address and thenrewrites the outgoing Internet Protocol (IP) packets on exit so that they appear to originate from the router. In the reverse communications path, responses are mapped back to the originating IP address using the rules ("state") stored in the translation tables. The translation table rules established in this fashion are flushed after a short period without new traffic refreshing their state. Asdescribed, the method enables communication through the router only when the conversation originates in the masqueraded network, since this establishes the translation tables. For example, a web browser in the masqueraded network can browse a website outside, but a web browser outside could not browse a web site in the masqueraded network. However, most NAT devices today allow the networkadministrator to configure translation table entries for permanent use. This feature is often referred to as "static NAT" or port forwarding and allows traffic originating in the 'outside' network to reach designated hosts in the masqueraded network.
– Because of the popularity of this technique (see below), the term NAT has become virtually synonymous with the method of IP masquerading.





•Network address translation has serious consequences (see below, Drawbacks, Benefits) on the quality of Internet connectivity and requires careful attention to the details of its implementation. As a result, many methods have been devised to alleviate the issues encountered. See article on NAT traversal.

NAT
Overview



In the mid-1990s NAT became a popular tool for alleviating the IPv4address exhaustion. It has become a standard, indispensable feature in routers for home and small-office Internet connections.
– Most systems using NAT do so in order to enable multiple hosts on a private network to access the Internet using a single public IP address (see gateway). However, NAT breaks the originally envisioned model of IP end-to-end connectivity across the Internet, introducescomplications in communication between hosts, and affects performance.



NAT obscures an internal network's structure: all traffic appears to outside parties as if it originated from the gateway machine. Network address translation involves re-writing the source and/or destination IP addresses and usually also the TCP/UDP port numbers of IP packets as they pass through the NAT. Checksums (bothIP and TCP/UDP) must also be rewritten to take account of the changes.
– In a typical configuration, a local network uses one of the designated "private" IP address subnets (the RFC 1918). Private Network Addresses are 192.168.x.x, 172.16.x.x through 172.31.x.x, and 10.x.x.x (or using CIDR notation, 192.168/16, 172.16/12, and 10/8), and a router on that network has a private address (such as...
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