TCPIP Protocol Suite & Utilities Revision no.: PPT/2K403/02
Comparing the TCP/IP protocol Suite, the OSI Model, and the DoD Model
Comparing the TCP/IP protocol Suite, the OSI Model, and the DoD Model (contd.) The TCP/IP protocol suite specifies functions above the Network Access layer of the DoD model and above the Data Link layer of the OSI model. The DoD networking model describes networking functions just like the OSI model, but it consists of only four layers : Process/Application Host-to-Host Internet Network Access
IP and the Internet Protocol Suite
IP Internetwork with Autonomous Systems
IP Internetwork with Autonomous Systems (contd.) An IP internetwork can be divided into logical groups referred to as autonomous systems. An autonomous system is a group of networks administered as a whole system by a single authority. Autonomous systems are interconnected using an exterior gateway protocol, such as Border Gateway Protocol (BGP) or Exterior Gateway Protocol (EGP).
Distance Vector Routing with RIP
Distance Vector Routing with RIP (contd.) Routing Information Protocol (RIP) is the TCP/IP suite s distance vector routing protocol. Routers A, B, and C connect LANs 1, 2,and 3. Router B broadcasts over LAN 2 that it is one hop from LAN 1. Router C, hearing this, then broadcasts to LAN 3 that it is two hops from LAN 1.
Distance Vector Routing with RIP (contd.) Hosts on LAN 3 also hear router A advertise that it is one hop from LAN 1, and they route all packets to LAN 1 through router A because it advertises the route with a lower metric. The cost associated with each route is a metric between 1 and 16. The metric usually represents a hop count. A route with a cost of 16 is considered to be unreachable.
Router Convergence and the Count-to-Infinity Problem
Router Convergence and the Count-to-Infinity Problem (contd.) A major problem with the RIP protocol is the amount of time it takes for all routers to synchronize their databases when a change occurs to the network (this process of synchronization is called convergence).
Split Horizon
Split Horizon (contd.) Split horizon decreases the amount of RIP traffic on the network, but it increases the time required for convergence.
Poison Reverse
Poison Reverse (contd.) When poison reverse is enabled, all routes learned from a network are advertised back to the same network with a cost of 16 (unreachable). Enabling poison reverse reduces the time taken by convergence, but increases the amount of RIP traffic on the network.
OSPF Routing
OSPF Routing (contd.) Link state routers build their route tables from packets distributed by other routers on the internetwork containing information about their directly connected interfaces and their costs. The main advantage of link state routing is that it minimizes the size of each router s routing table. The link state protocol most commonly used on IP internetworks is the Open Shortest Path First Protocol (OSPF).
OSPF Hello Packet
OSPF Hello Packet (contd.) The OSPF Hello protocol is responsible for establishing and maintaining neighbor relationships, or adjacencies, between routers connected to the same segment.
OSPF Database Synchronization
OSPF Database Synchronization (contd.) a. Each router exchanges database description packets (DDPs) with the DR and BDR. These packets include summary information. b. Upon receiving these packets, each OSPF router compares the information with the entries it has (from the neighbors list). c. If a database description packet has new or more up-todate information, the receiving router sends an LSR (link state request) packet to the router that has the information.
OSPF Database Synchronization (contd.) d. The router receiving the LSR packet replies with the needed information using an LSU (link state update) packet. After an LSU packet is received by the requesting router, the requesting router sends an LSA (link state acknowledgment packet) to acknowledge receipt of the new information.
OSPF Autonomous System
OSPF Autonomous System (contd.) Autonomous System. An autonomous system (AS) is a group of routers that exchange routing information using a common routing protocol in a single administrative unit.
OSPF Areas
OSPF Areas (contd.) The previous figure shows the EMA corporate network divided into areas. A separate area is established for each building on a campus. Backbone. A backbone is a logical area to which all other areas are connected. This special area must be directly connected to all other areas of the internetwork. The backbone s address is always 0.0.0.0. The routers that attach an area to the backbone are called Area Border Routers (ABRs).
Packet Routing
Packet Routing (contd.) Information sent between hosts is sent in packets that are often forwarded through many routers to reach their destinations. The Internet layer must perform the routing and packet switching to ensure that packets reach that final destination.
IP Header Format
Internet Protocol (IP) IP provides connectionless, non-guaranteed delivery of Transport layer packets (also called transport protocol data units (TPDUs) across an internetwork. Each TPDU or fragment is fitted with an IP header and transmitted as a frame by lower-layer protocols.
ICMP Redirect Messages
ICMP Redirect Messages (contd.) Redirect: This message is sent by an intermediate router to the source to inform it of a more optimal route to the destination. If you have not configured link-state routing on an IP host, routes might be automatically added to your routing table by ICMP.
ICMP Router Discovery
ICMP Router Discovery (contd.) Router discovery is not a routing protocol. It allows your host to discover neighboring routers, but it does not provide information about the best router to use to reach a destination. If a host chooses the incorrect router to reach a destination, it receives an ICMP redirect from that router identifying a better one.
ARP and RARP
ARP and RARP (contd.) Address Resolution Protocol (ARP) is the most widely used method of address resolution. The TCP/IP protocol suite uses ARP to map 4-byte software-based IP addresses to 6-byte hardware-based Data Link addresses. Reverse Address Resolution Protocol (RARP) is an extension of ARP. It is used to retrieve the IP address associated with a hardware address. This protocol is especially important for determining network addresses of diskless workstations.
ARP Operation
ARP Operation (contd.) Each system maintains a table that maps IP addresses to hardware addresses. The ARP protocol creates entries in this table as they are needed. If the ARP table does not contain the hardware address for your destination, a broadcast goes out to every host requesting the network address for that hardware.
ARP Operation (contd.) If the destination host is up and supports the ARP protocol, it will hear the broadcast and its network address. This address is added to the ARP table. To obtain the physical address of the destination, the host broadcasts an ARP packet and waits for the destination to respond.
TCP Header Format
TCP Header Format (contd.) TCP is the primary TCP/IP transport protocol. It accepts messages of any length from an upper-layer protocol (ULP) and provides full-duplex, acknowledged, connectionoriented, flow-controlled transport to a TCP peer in a remote network station. TCP transports data in a continuous, unstructured byte stream. Each segment is identified by a sequence number. To save time and make optimal use of transmission bandwidth, TCP supports numerous, simultaneous ULP conversations.
UDP Header Format
UDP Header Format (contd.) UDP, like TCP, provides transport services. Unlike TCP, UDP is not connection oriented and does not acknowledge data receipt. UDP simply accepts and transports datagrams from a ULP.
File Transfer Protocol
File Transfer Protocol (contd.) FTP also provides a variety of login, directory inspection, file manipulation, command execution, and other session control functions. These functions execute properly regardless of the host operating system and hardware platform. FTP uses virtual circuits to establish a reliable path between hosts. File transfers require an account and password as verification, or they can be configured for anonymous access.
Simple Mail Transfer Protocol
Simple Mail Transfer Protocol (contd.) SMTP specifies a standard for exchanging mail between workstations. This electronic mail routing application relies primarily on TCP to route mail messages between network hosts. SMTP does not provide the local mail user interface; it simply specifies how the message is passed from one host to another.
SNMP Architecture
Simple Network Management Protocol (SNMP) SNMP enables you to monitor a network from a single workstation called an SNMP manager. An SNMP manager can inspect or alter the objects contained within the agent s MIB. For example, from the SNMP manager you could examine the ARP table for another host and delete or change an incorrect entry.
Mapping the IPX/SPX Protocol Suite to the OSI Reference Model The IPX/SPX protocols are modular and layered, and do not fit neatly into the seven layers of the OSI model.
IPX Addresses
IPX Addresses (contd.) The primary purpose of IPX is to get packets through the entire internetwork. As workstations transmit data across the internetwork, IPX appends a header to the beginning of the data. SPX offers connection-oriented guaranteed delivery of packets. Hence, SPX requires overhead in buffer space and packets/second requirements.
IPX Addresses (contd.) IPX : Internetworking Packet Exchange SPX: Sequenced Packet Exchange Proper network addressing is one of the critical factors for successful routing in an internetwork. The preceding figure illustrates the routing of an IPX packet.
Internal IPX Address Operation
Internal Network Address The internal network address is an 8-digit (4-byte) hexadecimal number that enables the server to perform internal routing of services to the upper-layer protocols. You assign an IPX internal network number when you name the server.
IPX Packet Format IPX is a connectionless Network layer protocol that performs addressing and internetwork routing functions.
IPX Services Table
IPX Services Table (contd.)
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