CCNA Exploration Semester 1-Chapter 5 ppt

OSI network layer CCNA Exploration Semester Chapter 17-Jul-12 CCNA Exploration Semester 1 OSI network layer OSI model layer TCP/IP model Internet layer Application Presentation Session Transport Network Data link Physical 17-Jul-12 Data stream HTTP, FTP, TFTP, SMTP etc Segment TCP, UDP Packet IP Frame Ethernet, WAN technologies Bits CCNA Exploration Semester Application Transport Internet Network Access Network layer topics IP version – the most common layer routed protocol Dividing hosts into groups – why and how Routing – sending packets the right way Routing – how routers learn routes IP addressing – in chapter 17-Jul-12 CCNA Exploration Semester Purpose of layer Decide how to get the data from source to destination, then route it 17-Jul-12 CCNA Exploration Semester Layer protocol A layer protocol such as IP version must: Provide an addressing scheme to identify networks and individual hosts Encapsulate a segment from layer into a packet and include addresses Direct the packet across one or many networks to the destination host Decapsulate (remove the packet header) and give the segment to layer 17-Jul-12 CCNA Exploration Semester Network Layer – Communication from Host to Host Layer uses four basic processes: Addressing Encapsulation Routing: Intermediary devices that connect the networks are called routers The role of the router is to select paths for and direct packets toward their destination This process is known as routing Decapsulation 17-Jul-12 CCNA Exploration Semester Network layer protocols Internet Protocol version (IPv4) – the most common Internet Protocol version (IPv6) – designed to replace version eventually Novell Internetwork Packet Exchange (IPX) AppleTalk Connectionless Network Service (CLNS/DECNet) 17-Jul-12 CCNA Exploration Semester The roles of IPv4 protocol IPv4 is currently the most widely-used version of IP The Internet Protocol was designed as a protocol with low overhead It provides only the functions that are necessary to deliver a packet from a source to a destination over an interconnected system of networks The protocol was not designed to track and manage the flow of packets These functions are performed by other protocols in other layers 17-Jul-12 CCNA Exploration Semester IP characteristics Designed with low overhead for speed – it does only what it needs to Connectionless – does not set up connection with destination before sending packet Best effort (unreliable) no guarantee of safe delivery, no checking or resending Independent of media, but does need to know maximum packet size 17-Jul-12 CCNA Exploration Semester Connectionless IP does not notify the destination host Which layer protocol on the sending host will establish a connection? TCP: A connection-oriented protocol Which layer protocol on the sending host will not establish a connection? UDP: A connectionless protocol 17-Jul-12 CCNA Exploration Semester 10 Routing – First Look Network 192.168.1.0/24 Network 192.168.2.0/24 192.168.1.254/24 C 192.168.2.0/24 is direction connected, FastEthernet0/1 Routers learn about remote networks using: Static routes Dynamic Routing Protocol (R = RIP) Routes in a routing table have three main features: Destination network Next-hop Metric 17-Jul-12 CCNA Exploration Semester 35 Routing table and forwarding Each router has a routing table This contains a list of known networks and the best way to get there – outgoing port and address of nexthop router The router looks at the IP address of a packet It decides which network this address is on If it knows the network it forwards the packet If it does not know the network it drops the packet 17-Jul-12 CCNA Exploration Semester 36 Directly connected The networks of the router’s own interfaces go into the routing table 17-Jul-12 CCNA Exploration Semester 37 Other networks Routes to other networks can be configured by an administrator (static routes) Or they can be learned from another router using a routing protocol (dynamic routes) A router can have a default route Packets for unknown networks go on this route instead of being dropped 17-Jul-12 CCNA Exploration Semester 38 Routing table entries Directly connected shown by C 17-Jul-12 CCNA Exploration Semester 39 Routing table entries Static, configured by administrator, shown by S 17-Jul-12 CCNA Exploration Semester 40 Routing table entries Default, configured by administrator, shown by S* 17-Jul-12 CCNA Exploration Semester 41 Routing table entries Learned from another router using RIP routing protocol, shown by R 17-Jul-12 CCNA Exploration Semester 42 Router has a route 17-Jul-12 CCNA Exploration Semester 43 Routing protocols Routers learn routes from each other and put them in their routing tables A routing protocol is the set of rules they use to swap information These routes are dynamic routes Examples: Routing Information Protocol (RIP), Interior Gateway Routing Protocol (IGRP), Open Shortest Path First (OSPF), Border Gateway Protocol (BGP) and Enhanced IGRP (EIGRP 17-Jul-12 CCNA Exploration Semester 44 Routed versus Routing Routed protocol: used at the network layer that transfer data from one host to another across a router Routing protocols: allow routers to choose the best path for data from source to destination Examples: Internet Protocol (IP); Novell's Internetwork Packet Exchange (IPX); DECnet, AppleTalk, Banyan VINES, and Xerox Network Systems (XNS) 17-Jul-12 CCNA Exploration Semester 45 Default route A router can be configured to have a default route A default route is a route that will match all destination networks In IPv4 networks, the address 0.0.0.0 is used for this purpose The default route is used to forward packets for which there is no entry in the routing table for the destination network Packets with a destination network address that does not match a more specific route in the routing table are forwarded to the nexthop router associated with the default route 17-Jul-12 CCNA Exploration Semester 46 Static routes Dynamic routes Entered by administrator Time consuming, different for each router Must be updated if routes change Little processing No bandwidth used Gives nothing away 17-Jul-12 Learned from other routers Start the protocol then it runs by itself Automatically updates when routes change More processing Uses bandwidth Gives away information CCNA Exploration Semester 47 Labs 17-Jul-12 CCNA Exploration Semester 48 The End 17-Jul-12 CCNA Exploration Semester 49 ... part can vary 17-Jul-12 CCNA Exploration Semester 27 Message to same network 17-Jul-12 CCNA Exploration Semester 28 Message to different network 17-Jul-12 CCNA Exploration Semester 29 Default gateway... processing Uses bandwidth Gives away information CCNA Exploration Semester 47 Labs 17-Jul-12 CCNA Exploration Semester 48 The End 17-Jul-12 CCNA Exploration Semester 49 ... operating system TTL values are: UNIX: 255 Linux: 64 or 255 depending upon vendor and version Microsoft Windows 95: 32 Microsoft Vista: 128 17-Jul-12 CCNA Exploration Semester 16 IPv4 packet header fields