Petro passa para próxima Eliminatória

O Petro de Luanda é a única equipa angolana sobrevivente nas Afrotaças. O Petro Cilindrou o Ebusoua do Ghana por quatro bolas sem resposta. Os tricolores viam para esse jogo com uma desvantagem, fruto da derrota sofrida no Gana por duas bolas sem resposta.

Flávio por duas vezes, Gilberto e Keita foram os marcadores na tarde de domingo. 

O Petro defronta na próxima eliminatória o colosso africano Ismaily Sport Club do Egipto.

Bem haja Petro. 

ARP is used to find the MAC address that corresponds to an IP address: RARP is used to find the IP address that corresponds to a MAC address. True or False?

The answer is True.

Address Resolution Protocol (ARP) is a telecommunications protocol used for resolution of network layer addresses into link layer addresses, a critical function in multiple-access networks. ARP was defined by RFC 826 in 1982. It is Internet Standard STD 37. It is also the name of the program for manipulating these addresses in most operating systems.

ARP is used to convert an IP address to a physical address such as an Ethernet address.

ARP usually is implemented in the device drivers of network operating systems. It is most commonly seen on Ethernet networks, but ARP has also been implemented for ATM, Token Ring, and other physical networks. RFC 826 documented the initial design and implementation of ARP.

ARP works on Ethernet networks as follows. Ethernet network adapters are produced with a physical address embedded in the hardware called the Media Access Control (MAC) address. Manufacturers take care to ensure these 6-byte (48-bit) addresses are unique, and Ethernet relies on these unique identifiers for message delivery. When any device wishes to send data to another target device over Ethernet, it must first determine the MAC address of that target given its IP address These IP-to-MAC address mappings are derived from an ARP cache maintained on each device. If the given IP address does not appear in a device's cache, that device cannot direct messages to that target until it obtains a new mapping. To do this, the initiating device first sends an ARP request broadcast message on the local subnet. The host with the given IP address sends an ARP reply in response to the broadcat, allowing the initiating device to update its cache and proceed to deliver messages directly to the target.

Suppose that network addresses are scarce and are assigned so that they are not globally unique: in particular, suppose that the some block of addresses may be assigned to multiple organizations. How can the organization use these addresses? Can users from two such organizations communicate with each other?

To make the example concrete suppose that two organizations are assigned the same set of telephone numbers. Clearly, users within each organization can communicate with each other as long as they have a unique address within the organization. However, communications outside an organization poses a problem since any given address is no longer unique across multiple organizations.

A possible approach to enabling communications between users in different organizations is to use a two-step procedure as follows. Each organization has a special gateway to communicate outside the organization. Internal users contact the gateway to establish calls to other organizations. Gateways have procedures to establish connections with each other. This enables gateways to establish connections between their internal users and users in other networks