Network Protocols Internet Protocol IP mostly about IPv4 IPv6 is later TDC375 Spring 2009 10 John Kristoff DePaul University 1 Basic properties Connectionless service w o anything else its one way fire and forget no reliability performance or security guarantee Its relatively simple its the thin waist remember You can add some features to it Installed base makes this extremely difficult You can easily add features below or above With varying degrees of success benefit harm TDC375 Spring 2009 10 John Kristoff DePaul University 2 What does IP do for us Abstracts multiple and various data link nets below Provides a common global standard format Its glue we can use to connect things together Hardware application and packet independence Scalable routing mostly so far anyway TDC375 Spring 2009 10 John Kristoff DePaul University 3 The IPv4 datagram diagram courtesy of http www netbook cs purdue edu TDC375 Spring 2009 10 John Kristoff DePaul University 4 Inside an IP datagram Version field Usually set to binary 0100 is what in decimal Header length Length of IP header in 32 bit words 4 octets Typically set to 5 as in 5 4 octets 20 bytes Type of Service Tos redefined in newer RFCs An indication of quality class of service Rarely used with success outside a single AS TDC375 Spring 2009 10 John Kristoff DePaul University 5 Inside an IP datagram Total length total IP datagram length in octets maximum value is 65535 but rarely 1500 Identification to identify fragments of a single IP datagram Has had other experimental research usage Flags bit 0 reserved others for fragmentation handling DF MF TDC375 Spring 2009 10 John Kristoff DePaul University 6 Still inside and IP datagram Fragment offset helps piece together fragments Time to live TTL limts the number of router hops datagram incurs counts down to zero at zero it is discarded Protocol type indicates next upper layer protocol in payload Does it have to be an upper layer TDC375 Spring 2009 10 John Kristoff DePaul University 7 Inside the end of an IP datagram Header checksum Source Destination address 32 bit addresses Options optional duh used to verify header validity at each hop rarely used padded to 32 bit boundary if needed Payload which is the next protocol plus it s data variable length TDC375 Spring 2009 10 John Kristoff DePaul University 8
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