Internet ProtocolInternet ProtocolAn IP Internet – Network of NetworksProtocol Stack – IP is Common to AllService ModelIPv4 Header FormatFragmentation and ReassemblyExampleIPv4 Global AddressesDatagram ForwardingInternet Control Message Protocol (ICMP)ICMPEcho and Echo ReplyPing ExamplePowerPoint PresentationDestination UnreachableTime ExceededSource QuenchTracerouteTraceRoute ExampleCS 640 1Internet Protocol Outline Introduction to Internet ProtocolHeader and address formatsICMPToolsCS 640 2Internet Protocol•Runs on all hosts in the Internet and enables packets to be routed between systems–Key protocol for building networks–Kahn-Cerf•Datagram delivery of packets –Connectionless and based on routing protocols•Well defined packet format•Global addressing–Means for identifying Internet hosts•Fragmentation and reassembly–Since packets can be of varying size•Error reportingCS 640 3An IP Internet – Network of Networks R2R1H4H5H3H2H1Network 1 (Ethernet)H6Network 3 (FDDI)Network 4(point-to-point)H7 R3 H8Network 2 (Ethernet)CS 640 4Protocol Stack – IP is Common to All R1ETHFDDIIPIPETHTCPR2FDDIPPPIPR3PPPETHIPH1IPETHTCPH8CS 640 5Service Model•Connectionless (datagram-based)•Best-effort delivery (unreliable service)–packets are lost–packets are delivered out of order–duplicate copies of a packet are delivered–packets can be delayed for a long time•Datagram formatVersion HLenTOS LengthIdent Flags OffsetTTL Protocol ChecksumSourceAddrDestinationAddrOptions (variable)Pad(variable)0 4 8 16 19 31DataCS 640 6IPv4 Header FormatVersion HLenTOS LengthIdent Flags OffsetTTL Protocol ChecksumSourceAddrDestinationAddrOptions (variable)Pad(variable)0 4 8 16 19 31DataCS 640 7Fragmentation and Reassembly•Each network has some Maximum Transmission Unit (MTU)–Largest datagram that a network can carry in a frame•Strategy–fragment when necessary (MTU < Datagram)–try to avoid fragmentation at source host•Due to overhead of reassembly–re-fragmentation is possible –fragments are self-contained datagrams–delay reassembly until destination host•Keep this functionality out of the network–do not recover from lost fragments •End hosts try to reassemble fragmented packets –if a fragment is lost…•End hosts are encouraged to do MTU discoveryCS 640 8Example H1 R1 R2 R3 H8ETH IP (1400) FDDI IP (1400) PPP IP (512)PPP IP (376)PPP IP (512)ETH IP (512)ETH IP (376)ETH IP (512)CS 640 9 Ident = x Offset = 0Start of header0Rest of header1400 data bytesIdent = x Offset = 0Start of header1Rest of header512 data bytesIdent = x Offset = 512Start of header1Rest of header512 data bytesIdent = x Offset = 1024Start of header0Rest of header376 data bytesCS 640 10IPv4 Global Addresses•Properties–globally unique–hierarchical: network + host•Dot Notation–10.3.2.4–128.96.33.81–192.12.69.77•AS’s refer to a networktype (assigned address range)Network Host7 240A:Network Host14 161 0B:Network Host21 81 1 0C:CS 640 11Datagram Forwarding •Every datagram contains destination’s address•The “network part” of an IP address uniquely identifies a single physical network (AS)•If directly connected to destination network, then forward to host•If not directly connected to destination network, then forward to some router•Forwarding table maps network number into next hop–Mapping is based on routing algorithm•Each host has a default router•Each router maintains a forwarding tableCS 640 12Internet Control Message Protocol (ICMP)•Echo (ping)•Redirect (from router to source host)•Destination unreachable (protocol, port, or host)•TTL exceeded (so datagrams don’t cycle forever)•Checksum failed •Reassembly failed•Cannot fragmentCS 640 13ICMP•Uses IP but is a separate protocol in the network layerICMP HEADERIP HEADERPROTOCOL = 1TYPE CODE CHECKSUMREMAINDER OF ICMP MESSAGE (FORMAT IS TYPESPECIFIC)IP HEADERIP DATACS 640 14Echo and Echo ReplyTYPE CODE CHECKSUMIDENTIFIER SEQUENCE #DATA ….TYPE: 8 = ECHO, 0 = ECHO REPLY CODE; CODE = 0IDENTIFIERAn identifier to aid in matching echoes and repliesSEQUENCE #Same use as for IDENTIFIERUNIX “ping” uses echo/echo replyCS 640 15Ping Example C:\WINDOWS\Desktop>ping www.soi.wide.ad.jp Pinging asari.soi.wide.ad.jp [203.178.137.88] with 32 bytes of data: Reply from 203.178.137.88: bytes=32 time=253ms TTL=240 Reply from 203.178.137.88: bytes=32 time=231ms TTL=240 Reply from 203.178.137.88: bytes=32 time=225ms TTL=240 Reply from 203.178.137.88: bytes=32 time=214ms TTL=240 Ping statistics for 203.178.137.88: Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),Approximate round trip times in milli-seconds: Minimum = 214ms, Maximum = 253ms, Average = 230msCS 640 16Redirect when no route to DestinationTYPE CODE CHECKSUMNEW ROUTER ADDRESSIP HEADER + 64 bits data from original DGTYPE = 5CODE = 0 = Network redirect1 = Host redirect2 = Network redirect for specific TOS3 = Host redirect for specific TOSCS 640 17Destination UnreachableTYPE CODE CHECKSUMUNUSEDIP HEADER + 64 bits data from original DG TYPE = 3CODE 0 = Net unreachable1 = Host unreachable2= Protocol unreachable3 = Port unreachable4 = Fragmentation needed but DF set5 = Source route failedCS 640 18Time ExceededTYPE CODE CHECKSUMUNUSEDIP HEADER + 64 bits data from original DG TYPE = 11CODE0 = Time to live exceeded in transit1 = Fragment reassembly time exceededCS 640 19Source QuenchTYPE CODE CHECKSUMUNUSEDIP HEADER + 64 bits data from original DG TYPE = 4; CODE = 0Indicates that a router has dropped the original DG or may indicate that a router is approaching its capacity limit.Correct behavior for source host is not defined.CS 640 20Traceroute•UNIX utility - displays router used to get to a specified Internet Host•Operation –router sends ICMP Time Exceeded message to source if TTL is decremented to 0–if TTL starts at 5, source host will receive Time Exceeded message from router that is 5 hopes away•Traceroute sends a series of probes with different TTL values… and records the source address of the ICMP Time Exceeded message for each•Probes are formatted to that the destination host will send an ICMP Port Unreachable messageCS 640 21TraceRoute ExampleC:\windows\desktop> tracert www.soi.wide.ad.jpTracing route to asari.soi.wide.ad.jp [203.178.137.88]over a maximum of 30 hops: 1 19 ms 27 ms 23 ms 208.166.201.1 2 17 ms 13 ms 14 ms 204.189.71.9 3 25 ms 29 ms 29 ms
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