Checksum 16 of the header only destaddr srcaddr 32

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Checksum (16): of the header only DestAddr & SrcAddr (32) Version HLen TOS Length Ident Flags Offset TTL Protocol Checksum SourceAddr DestinationAddr Options (variable) Pad (variable) 0 4 8 16 19 31 Data
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Datagram Forwarding Strategy every datagram contains destination's address if directly connected to destination network, then forward to host if not directly connected to destination network, then forward to some router each host has a default router each router maintains a forwarding table forwarding table maps network number into next hop
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My machine C:\>netstat -r Network destination Netmask Gateway Interface Metric 0.0.0.0 0.0.0.0 128.187.172.1 128.187.172.116 1 127.0.0.0 255.0.0.0 127.0.0.1 127.0.0.1 1 128.187.172.0 255.255.255.0 128.187.172.116 128.187.172.116 1 128.187.172.116 255.255.255.255 127.0.0.1 127.0.0.1 1 128.187.255.255 255.255.255.255 128.187.172.116 128.187.172.116 1 255.255.255.255 255.255.255.255 128.187.172.116 128.187.172.116 1
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Reliable Byte-Stream (TCP)
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Overview Byte-stream sending process writes some number of bytes TCP breaks into segments and sends via IP receiving process reads some number of bytes Full duplex Connection-oriented (Reliable) Every segment is numbered & acknowledged Flow control: keep sender from overrunning receiver Congestion control: keep sender from overrunning network
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TCP Stream segment segment segment . . . Transmit Segments . . . Appl Process Write Bytes Appl Process . . . Read Bytes TCP send buffer TCP receive buffer
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Issues Potentially long delay in network need to be prepared for arrival of very old packets (limit 60 seconds) Potentially different capacity at destination need to accommodate different amounts of buffering (end hosts may have hundreds of applications) Potentially different network capacity need to be prepared for network congestion
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Segment Format Each connection identified with 4- tuple: <SrcPort, SrcIPAddr, DstPort, DstIPAddr> Sliding window + flow control Acknowledgment, SequenceNum, AdvertisedWindow Flags: SYN, FIN, RESET, PUSH, URG, ACK Checksum: pseudo header + tcp header + data Src Port Dest Port Advertised Window Acknowledgement SequenceNum CheckSum Flags options UrgPtr 0 (4) (6) (6) (variable) data HdrLen
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TCP Flow Sender Receiver Data (SequenceNum) Acknowledgement + AdvertisedWindow
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DNS (Domain Name Service)
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DNS People don’t remember 32-bit numbers very well Instead of using IP addresses, map the IP address to a name People remember names better Translation of names to IP addresses is done by name servers Originally done by files on each host
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DNS Basically, it is a distributed database Distributed administration Distributed load Distributed security problems Robustness and performance through Replication Caching
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DNS Hierarchical You can give away control of part of the tree beneath you Process Issue request If found, return If not Ask higher edu Education level Name Server UofU BYU Region Name Server ACS CS Local Name Server etc Root Name Server
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DNS Name Space
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DNS Lookup flits.cs.vu.nl linda.cs.yale.edu
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DNS Client-Server application Normally uses UDP (port 53) Three Roles
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  • Winter '08
  • Clement,M
  • Transmission Control Protocol, Domain Name System, int sock, data link physical, network data link

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