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| router | a type of internetworking device that passes data packets between networks based on Layer 3 addresses. A router has the ability to make intelligent decisions regarding the best path for delivery of data on the network. |
| ARP | Address Resolution Protocol |
| RARP | Reverse Address Resolution Protocol |
| 2 networking address schemes | one uses the MAC address, a data link (Layer 2) address; the other uses an address located at the network layer (Layer 3) of the OSI model |
| router's attachment to a network | interface or port |
| two methods for assigning IP addresses | static addressing and dynamic addressing |
| Static Addressing | go to each individual device and configure it with an IP address. This method requires you to keep very meticulous records |
| Dynamic Addressing | 1) Reverse Address Resolution Protocol (RARP) ; 2) BOOTstrap Protocol (BOOTP) ; 3) Dynamic Host Configuration Protocol (DHCP) |
| Reverse address resolution protocol (RARP) | Reverse address resolution protocol (RARP) binds MAC addresses to IP addresses. This binding allows some network devices to encapsulate data before sending them out on the network. A network device such as a diskless workstation might know its MAC address, but not its IP address. Devices using RARP require that a RARP server be present on the network to answer RARP requests. |
| BOOTstrap protocol (BOOTP) | · A device uses BOOTstrap protocol (BOOTP) when it starts up, to obtain an IP address. BOOTP uses UDP to carry messages; the UDP message is encapsulated in an IP datagram. A computer uses BOOTP to send a broadcast IP datagram (using a destination IP address of all 1s - 255.255.255.255). A BOOTP server receives the broadcast and then sends a broadcast. The client receives a datagram and checks the MAC address. If it finds its own MAC address in the destination address field, then it takes the IP address in that datagram. Like RARP, BOOTP operates in a client-server environment, and only requires a single packet exchange. However, unlike RARP, which only sends back a 4 octet IP address, BOOTP datagrams can include the IP address, the address of a router (default gateway), the address of a server, and a vendor-specific field. One of the problems with BOOTP is that it was not designed to provide dynamic address assignment. With BOOTP you create a configuration file that specifies the parameters for each device. |
| · Dynamic host configuration protocol (DHCP) | · Dynamic host configuration protocol (DHCP) has been proposed as a successor to BOOTP. Unlike BOOTP, DHCP allows a host to obtain an IP address quickly and dynamically. All that is required using DHCP is a defined range of IP addresses on a DHCP server. As hosts come online they contact the DHCP server and request an address. The DHCP server chooses an address and allocates it to that host. With DHCP, the entire computer's configuration can be obtained in one message (e.g. along with the IP address, the server can also send a subnet mask). |
| DHCP initialization sequence | 1) DHCPDISCOVER; 2) DHCPOFFER; 3) DHCPREQUEST packet; 4) DHCPACK OR initialize, select, negotiate, bound |
| DHCPDISCOVER | broadcast messages, which are UDP packets with the port number set to the BOOTP port |
| DHCPOFFER | After sending the DHCPDISCOVER packets, the client moves into the select state and collects DHCPOFFER responses from DHCP server |
| DHCPREQUEST | The client then selects the first response it receives and negotiates lease time (the length of time it can keep the address without renewing it) with the DHCP server by sending a DHCPREQUEST packet |
| DHCPACK | The DHCP server acknowledges a client request with a DHCPACK packet. The client can now enter the bound state and begin using the address |
| Function of the address resolution protocol (ARP) | When a source determines the IP address for a destination, the source consults its ARP table in order to locate the MAC address for the destination. If the source locates an entry in its table (destination IP address to destination MAC address), it binds, or associates, the IP address to the MAC address and uses it to encapsulate the data. |
| default gateway | the IP address of the interface on the router that connects to the network segment on which the source host is located. The default gateway's IP address must be in the same network segment as the source host. |
| Proxy ARP | In this case an intermediate device (e.g. router) sends an ARP response, on behalf of an end node. Routers running proxy ARP capture ARP packets. They respond with their MAC addresses for those requests in which the IP address is not in the range of addresses of the local subnet. |
| Common Routed Protocols | TCP/IP; IPX/SPX; AppleTalk |
| Non-routed protocol | NetBEUI |
| Examples of routing protocols | Routing Information Protocol (RIP), the Interior Gateway Routing Protocol (IGRP), the Enhanced Interior Gateway Routing Protocol (EIGRP),and Open Shortest Path First (OSPF). |
| Definition of routing protocol | to exchange routing tables and to share routing information |
| distance-vector | calculates distances to a destination host in terms of a metric such as hops (i.e. how many routers) a packet must pass through |
| RIP | RIP enables routers to update their routing tables at programmable intervals, usually every 30 seconds; distance-vector; doesn’t always use the fastest path to a destination; one of the earliest routing protocols to be developed; maximum number of hops that data can be forwarded through is fifteen |
| connectionless delivery system | In a connectionless system the destination is not contacted before a packet is sent |
| connection-oriented systems | a connection is established between the sender and the recipient before any data is transferred |
| packet switched | as the packets pass from source to destination, they can switch to different paths |
| circuit switched | establish a connection with the recipient, first, and then begin the data transfer. |
| indirect routing | If the router cannot locate the mapped destination address and MAC address of the device of the final target device, it locates the MAC address of another router that can perform this function, and forwards the data to that router |
| Link State | Open Shortest Path First (OSPF) |
| Most common form of routing protocol | RIP. This Interior Gateway Protocol calculates distances to a destination. |
| IGRP and EIGRP | protocols that were developed by Cisco Systems, Inc., therefore, they are considered proprietary routing protocols. |
| IGRP | developed specifically to address problems associated with routing in large multi-vendor networks that were beyond the scope of protocols such as RIP. Like RIP, IGRP is a distance-vector protocol; |
| EIGRP | an advanced version of IGRP. Specifically, EIGRP provides superior operating efficiency and combines the advantages of link-state protocols with those of distance-vector protocols |
| stub network | when there is only one path to a destination network |
