ccna 200-301 network simulator tools plus waterbury

ccna 200-301 network simulator tools plus waterbury.31___________________________________________By default, proxy ARP is enabled on all Cisco router Ethernet interfaces. If you do not intend to use it, you can disable it by using the "noipproxy-arp" command under the router interface. For the use of proxy ARP, please refer to the video file "Video \5-l.wrr o" in the CD. 5.RARP (ReverseAddress ResolutionProtocol) The ARP described earlier is to query the MAC address of other computers with the known IP address of other computers. RARP, on the other hand, asks for the IP address of the local computer when the MAC address of the local computer is known. Typically used on diskless workstations, when a diskless workstation boots up, it has no way of knowing its IP address at its initialization, however, it can know its MAC address. The diskless workstation can ask for the IP address corresponding to this MAC address by sending a packet of RARP, and a computer on the network, called a RARP server, is assigned to respond to this request so that the diskless workstation will get its IP address. RARP is an early solution provided to obtain IP through hardware address, but it has its own limitations, for example, RARP client and RARP server are not in the same network segment, and there are devices such as routers connected in between, then using RARP is powerless, because RARP request message cannot pass through the router. The BOOTP (BootstrapProtocol) protocol provides a good solution to this problem, and the DHCP (DynamicHostConfigurationProtocol) protocol is also one of the common protocols used in today's medium and large networks. BOOTP and DHCP are briefly introduced next.BOOTP: BOOTP is also a client/server protocol that provides IP addresses, subnet masks, gateways (router addresses), and DNS information for diskless operating systems or for computers configured to obtain them dynamically. The implementation process is divided into two cases.. Case 1: This works in the same environment as RARP, i.e., the client and server are on the same network segment, the BOOTP server passively opens UDP port 67, the client sends the request through UDP port 68, because the client does not know its IP address and does not know the server's IP address, the client uses an all-0 source address with an all-1 destination address, and the server responds via unicast or broadcast. .. Case 2: The client and server are on different network segments, and the way to achieve this is to set up a relay agent in each segment, the relay agent knows the server's address, and when it receives a broadcast message with a destination port of 67, it encapsulates the message as a unicast datagram and sends it to the BOOTP server, and the server knows that the message comes from the relay agent because it has its IP address in the message sent by the relay agent. The relay agent receives the response from the BOOTP server and sends it to the BOOTP requesting client oDHCP: DHCP is similar to the BOOTP protocol, but DHCP is more powerful, not only allowing for easy dynamic assignment through leases, but also providing dozens of network parameters in addition to IP addresses, subnet masks, gateways, and DNS. ARP, Proxy ARP, and RARP are also part of the network access layer, and it can be said that the ARP protocol spans layers two and three of the OSI seven-layer model. Because of this, some firewalls at the network layer appear to be powerless against lower-level ARP attacks.2.4.3 Transport Layer**In a TCP/IP network, IP uses a connectionless datagram mechanism to deliver data on a "best-effort basis", i.e., it simply delivers the message to the destination host on a best-effort basis, regardless of whether the transmission is correct or not, without verification, acknowledgement, or guaranteeing the order of the messages. The reliability of TCP/IP is reflected in the transport layer, where one of the transport layer protocols, TCP, provides connection-oriented services (the other transport layer protocol, UDP, is connectionless). o The primary function of the transport layer is to reliably and accurately transmit and