Unformatted text preview: -ip-illustrated/link_lay.htm (11 of 11) [12/09/2001 14.46.33] Chapter 3. IP: Internet Protocol IP: Internet Protocol
IP is the workhorse protocol of the TCP/IP protocol suite. All TCP, UDP, ICMP, and IGMP data
gets transmitted as IP datagrams (Figure 1.4). A fact that amazes many newcomers to TCP/IP,
especially those from an X.25 or SNA background, is that IP provides an unreliable, connectionless
datagram delivery service.
By unreliable we mean there are no guarantees that an IP datagram successfully gets to its
destination. IP provides a best effort service. When something goes wrong, such as a router
temporarily running out of buffers, IP has a simple error handling algorithm: throw away the
datagram and try to send an ICMP message back to the source. Any required reliability must be
provided by the upper layers (e.g., TCP).
The term connectionless means that IP does not maintain any state information about successive
datagrams. Each datagram is handled independently from all other datagrams. This also means that
IP datagrams can get delivered out of order. If a source sends two consecutive datagrams (first A,
then B) to the same destination, each is routed independently and can take different routes, with B
arriving before A.
In this chapter we take a brief look at the fields in the IP header, describe IP routing, and cover
subnetting. We also look at two useful commands: ifconfig and netstat. We leave a detailed
discussion of some of the fields in the IP header for later when we can see exactly how the fields
are used. RFC 791 [Postel 1981a] is the official specification of IP. 3.2 IP Header
Figure 3.1 shows the format of an IP datagram. The normal size of the IP header is 20 bytes, unless
options are present. file:///D|/Documents%20and%20Settings/bigini/Docum.../homenet2run/tcpip/tcp-ip-illustrated/ip_inter.htm (1 of 19) [12/09/2001 14.46.37] Chapter 3. IP: Internet Protocol Figure 3.1 IP datagram, showing the fields in the IP header.
We will show the pictures of...
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This test prep was uploaded on 04/04/2014 for the course ECE EL5373 taught by Professor Guoyang during the Spring '12 term at NYU Poly.
- Spring '12